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W3C

XQuery 4.0: An XML Query Language

W3C Editor's Draft 1719 December 2024

This version:
https://qt4cg.org/specifications/pr/1666/xquery-40/
Most recent version of XQuery:
https://qt4cg.org/specifications/xquery-40/
Most recent Recommendation of XQuery:
https://www.w3.org/TR/2017/REC-xquery-31-20170321/
Editor:
Michael Kay, Saxonica <mike@saxonica.com>

Please check the errata for any errors or issues reported since publication.

See also translations.


Abstract

XML is a versatile markup language, capable of labeling the information content of diverse data sources, including structured and semi-structured documents, relational databases, and object repositories. A query language that uses the structure of XML intelligently can express queries across all these kinds of data, whether physically stored in XML or viewed as XML via middleware. This specification describes a query language called XQuery, which is designed to be broadly applicable across many types of XML data sources.

A list of changes made since XQuery 3.1 can be found in K Change Log.

Status of this Document

This is a draft prepared by the QT4CG (officially registered in W3C as the XSLT Extensions Community Group). Comments are invited.


1 Introduction

Changes in 4.0 

  1. Use the arrows to browse significant changes since the 3.1 version of this specification.

  2. Sections with significant changes are marked Δ in the table of contents.

As increasing amounts of information are stored, exchanged, and presented using XML, the ability to intelligently query XML data sources becomes increasingly important. One of the great strengths of XML is its flexibility in representing many different kinds of information from diverse sources. To exploit this flexibility, an XML query language must provide features for retrieving and interpreting information from these diverse sources.

As increasing amounts of JSON are used for lightweight data-exchange, an XML query language for Web data needs to handle JSON as well as XML and HTML.

XQuery is designed to be a language in which queries are concise and easily understood. It is also flexible enough to query a broad spectrum of information sources, both XML and non-XML, including both databases and documents. XQuery was originally derived from an XML query language called Quilt [Quilt], which in turn borrowed features from several other languages, including XPath 1.0 [XML Path Language (XPath) Version 1.0], XQL [XQL], XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].

[Definition: XQuery 4.0 operates on the abstract, logical structure of an XML document or JSON object rather than its surface syntax. This logical structure, known as the data model, is defined in [XQuery and XPath Data Model (XDM) 4.0].]

XQuery 4.0 is an extension of XPath 4.0. In general, any expression that is syntactically valid and executes successfully in both XPath 4.0 and XQuery 4.0 will return the same result in both languages. There are a few exceptions to this rule:

Because these languages are so closely related, their grammars and language descriptions are generated from a common source to ensure consistency.

XQuery 4.0 also depends on and is closely related to the following specifications:

Note:

The XML-based syntax for XQuery known as XQueryX is no longer maintained.

[Definition: An XQuery 4.0 Processor processes a query according to the XQuery 4.0 specification. ] [Definition: An XQuery 3.1 Processor processes a query according to the XQuery 3.1 specification. ] [Definition: An XQuery 3.0 Processor processes a query according to the XQuery 3.0 specification. ] [Definition: An XQuery 1.0 Processor processes a query according to the XQuery 1.0 specification. ]

This document specifies a grammar for XQuery 4.0, using the same basic EBNF notation used in [XML 1.0]. Unless otherwise noted (see A.3 Lexical structure), whitespace is not significant in queries. Grammar productions are introduced together with the features that they describe, and a complete grammar is also presented in the appendix [A XQuery 4.0 Grammar]. The appendix is the normative version.

In the grammar productions in this document, named symbols are underlined and literal text is enclosed in double quotes. For example, the following productions describe the syntax of a static function call:

FunctionCall::=EQNameArgumentList
/* xgc: reserved-function-names */
/* gn: parens */
ArgumentList::="(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"

The productions should be read as follows: A function call consists of an EQName followed by an ArgumentList. The argument list consists of an opening parenthesis, an optional list of one or more arguments (separated by commas), and a closing parenthesis.

This document normatively defines the static and dynamic semantics of XQuery 4.0. In this document, examples and material labeled as “Note” are provided for explanatory purposes and are not normative.

2 Basics

2.1 Terminology

Changes in 4.0  

  1. The EBNF operators ++ and ** have been introduced, for more concise representation of sequences using a character such as "," as a separator. The notation is borrowed from Invisible XML.  [Issue 1366 PR 1498]

The basic building block of XQuery 4.0 is the expression, which is a string of [Unicode] characters; the version of Unicode to be used is implementation-defined. The language provides several kinds of expressions which may be constructed from keywords, symbols, and operands. In general, the operands of an expression are other expressions. XQuery 4.0 allows expressions to be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitution if the variable declaration contains construction of new nodes.)

Note:

This specification contains no assumptions or requirements regarding the character set encoding of strings of [Unicode] characters.

Like XML, XQuery 4.0 is a case-sensitive language. Keywords in XQuery 4.0 use lower-case characters and are not reserved—that is, names in XQuery 4.0 expressions are allowed to be the same as language keywords, except for certain unprefixed function-names listed in A.4 Reserved Function Names.

In this specification the phrases must, must not, should, should not, may, required, and recommended, when used in normative text and rendered in small capitals, are to be interpreted as described in [RFC2119].

Certain aspects of language processing are described in this specification as implementation-defined or implementation-dependent.

  • [Definition: Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementer for each particular implementation.]

  • [Definition: Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementer for any particular implementation.]

2.1.1 Grammar Notation

Changes in 4.0  

  1. The EBNF notation has been extended to allow the constructs (A ++ ",") (one or more occurrences of A, comma-separated, and (A ** ",") (zero or more occurrences of A, comma-separated.   [Issue 1366 PR 1498 30 October 2024]

The grammar of XQuery 4.0 is defined using a version of EBNF defined in A.1.1 Notation. The notation is based on the EBNF dialect used in the XML specification, with two notable additions derived from the Invisible XML grammar:

(A ++ ",") represents a sequence of one or more comma-separated occurrences of A.

(A ** ",") represents a sequence of zero or more comma-separated occurrences of A.

For example the following production rule indicates that an Expr consists of one or more occurrences of ExprSingle, separated by commas:

Expr::=(ExprSingle ++ ",")

In principle any production can be used for the separator, but in practice this notation is only used in cases where the separator is a simple constant string.

EBNF grammar rules appear throughout the specification for ease of reference, and the entire grammar is summarized in A.1 EBNF. For XQuery 4.0, the top-level production rule is Module, representing an XQuery module.

2.1.2 Values

Changes in 4.0  

  1. The term atomic value has been replaced by atomic item.   [Issue 1337 PR 1361 2 August 2024]

[Definition: In the data model, a value is always a sequence.]

[Definition: A sequence is an ordered collection of zero or more items.]

[Definition: An item is either an atomic item, a node, or a function item.]

[Definition: An atomic item is a value in the value space of an atomic type, as defined in [XML Schema 1.0] or [XML Schema 1.1].]

[Definition: A node is an instance of one of the node kinds defined in Section 5 NodesDM.] Each node has a unique node identity, a typed value, and a string value. In addition, some nodes have a name. The typed value of a node is a sequence of zero or more atomic items. The string value of a node is a value of type xs:string. The name of a node is a value of type xs:QName.

[Definition: A function item is an item that can be called using a dynamic function call.]

Maps (see 4.14.1 Maps) and arrays (see 4.14.2 Arrays) are specific kinds of function items.

[Definition: A sequence containing exactly one item is called a singleton.] An item is identical to a singleton sequence containing that item. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3). [Definition: A sequence containing zero items is called an empty sequence.]

[Definition: The term XDM instance is used, synonymously with the term value, to denote an unconstrained sequence of items.]

Element nodes have a property called in-scope namespaces. [Definition: The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI.] For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.

Note:

In [XML Path Language (XPath) Version 1.0], the in-scope namespaces of an element node are represented by a collection of namespace nodes arranged on a namespace axis, which is optional and deprecated in [XPath 4.0]. XQuery does not support the namespace axis and does not represent namespace bindings in the form of nodes.

However, where other specifications such as [XSLT and XQuery Serialization 4.0] refer to namespace nodes, these nodes may be synthesized from the in-scope namespaces of an element node by interpreting each namespace binding as a namespace node. An application that needs to create a set of namespace nodes to represent these bindings for an element bound to $e can do so using the following code.

in-scope-prefixes($e) ! namespace {.}{ namespace-uri-for-prefix(., $e)}

2.1.3 Namespaces and QNames

[Definition: An expanded QName is a triple: its components are a prefix, a local name, and a namespace URI. In the case of a name in no namespace, the namespace URI and prefix are both absent. In the case of a name in the default namespace, the prefix is absent.] When comparing two expanded QNames, the prefixes are ignored: the local name parts must be equal under the Unicode codepoint collation (Section 5.3.1 CollationsFO), and the namespace URI parts must either both be absent, or must be equal under the Unicode codepoint collation.

In the XQuery 4.0 grammar, QNames representing the names of elements, attributes, functions, variables, types, or other such constructs are written as instances of the grammatical production EQName.

EQName::=QName | URIQualifiedName
QName::=[http://www.w3.org/TR/REC-xml-names/#NT-QName]Names
/* xgc: xml-version */
URILiteral::=StringLiteral
URIQualifiedName::=BracedURILiteralNCName
/* ws: explicit */
BracedURILiteral::="Q" "{" (PredefinedEntityRef | CharRef | [^&{}])* "}"
/* ws: explicit */
NCName::=[http://www.w3.org/TR/REC-xml-names/#NT-NCName]Names
/* xgc: xml-version */

The EQName production allows a QName to be written in one of three ways:

  • local-name only (for example, invoice).

    A name written in this form has no prefix, and the rules for determining the namespace depend on the context in which the name appears. This form is a lexical QName.

  • prefix plus local-name (for example, my:invoice).

    In this case the prefix and local name of the QName are as written, and the namespace URI is inferred from the prefix by examining the in-scope namespaces in the static context where the QName appears; the context must include a binding for the prefix. This form is a lexical QName.

  • URI plus local-name (for example, Q{http://example.com/ns}invoice).

    In this case the local name and namespace URI are as written, and the prefix is absent. This way of writing a QName is context-free, which makes it particularly suitable for use in queries that are generated by software. This form is a URIQualifiedName. If the BracedURILiteral has no content (for example, Q{}invoice) then the namespace URI of the QName is absent.

[Definition: A lexical QName is a name that conforms to the syntax of the QName production].

The namespace URI value in a URIQualifiedName is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2. It is a static error [err:XQST0070] if the namespace URI for an EQName is http://www.w3.org/2000/xmlns/.

Here are some examples of EQNames:

This document uses the following namespace prefixes to represent the namespace URIs with which they are listed. Although these prefixes are used within this specification to refer to the corresponding namespaces, not all of these bindings will necessarily be present in the static context of every expression, and authors are free to use different prefixes for these namespaces, or to bind these prefixes to different namespaces.

  • xml: http://www.w3.org/XML/1998/namespace

  • xs: http://www.w3.org/2001/XMLSchema

  • xsi: http://www.w3.org/2001/XMLSchema-instance

  • fn: http://www.w3.org/2005/xpath-functions

  • array: http://www.w3.org/2005/xpath-functions/array

  • map: http://www.w3.org/2005/xpath-functions/map

  • math: http://www.w3.org/2005/xpath-functions/math

  • err: http://www.w3.org/2005/xqt-errors (see 2.4.2 Identifying and Reporting Errors).

  • local: http://www.w3.org/2005/xquery-local-functions (see 5.18 Function Declarations.)

  • output: http://www.w3.org/2010/xslt-xquery-serialization

  • xq: http://www.w3.org/2012/xquery

[Definition: Within this specification, the term URI refers to a Universal Resource Identifier as defined in [RFC3986] and extended in [RFC3987] with the new name IRI.] The term URI has been retained in preference to IRI to avoid introducing new names for concepts such as “Base URI” that are defined or referenced across the whole family of XML specifications.

Note:

In most contexts, processors are not required to raise errors if a URI is not lexically valid according to [RFC3986] and [RFC3987]. See 2.5.5 URI Literalsand 4.12.1.2 Namespace Declaration Attributes for details.

2.2 Expression Context

[Definition: The expression context for a given expression consists of all the information that can affect the result of the expression.]

This information is organized into two categories called the static context and the dynamic context.

2.2.1 Static Context

Changes in 4.0  

  1. The default namespace for elements and types can be set to the value ##any, allowing unprefixed names in axis steps to match elements with a given local name in any namespace.   [Issue 296 PR 1181 30 April 2024]

  2. Parts of the static context that were there purely to assist in static typing, such as the statically known documents, were no longer referenced and have therefore been dropped.   [Issue 1343 PR 1344 23 September 2024]

  3. The context value static type, which was there purely to assist in static typing, has been dropped.   [Issue 1495 ]

[Definition: The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.] This information can be used to decide whether the expression contains a static error.

The individual components of the static context are described below.

In XQuery 4.0, the static context for an expression is largely defined in the query prolog of a module: see 5 Modules and Prologs. Declarations in the prolog, such as variable declarations, function declarations, and decimal format declarations populate the static context for expressions appearing within the module. In some cases (but not all) these declarations may affect the static context for expressions that precede the relevant declaration. The static context can also be affected by declarations in other modules that are referenced using an import module declaration: see 5.12 Module Import.

In addition, some expressions modify the static context for their subexpressions. The most obvious example is in-scope variables (a FLWORExpr declares bindings of local variables that are available for reference within subsequent clauses of the expression). A further example is the statically known namespaces: an element constructor may contain namespace declarations such as xmlns:p="some_uri" which cause additional namespace prefixes to be available within the content of the element constructor.

Appendix C.1 Static Context Components gives an overview of the components in the static context and the way they are initialized.

Some components of the static context, but not all, also affect the dynamic semantics of expressions. For example, casting of a string such as "xbrl:xbrl" to an xs:QName might expand the prefix xbrl to the namespace URI http://www.xbrl.org/2003/instance using the statically known namespaces from the static context; since the input string "xbrl:xbrl" is in general not known until execution time (it might be read from a source document), this means that the values of the statically known namespaces must be available at execution time.

  • [Definition: XPath 1.0 compatibility mode.This component must be set by all host languages that include XPath 3.1 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false. ]

  • [Definition: Statically known namespaces. This is a mapping from prefix to namespace URI that defines all the namespaces that are known during static processing of a given expression.]

    The URI value is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2.

    The statically known namespaces may include a binding for the zero-length prefix; however, this is used only in limited circumstances because the rules for resolving unprefixed QNames depend on how such a name is used.

    Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression.

    Some namespaces are predefined; additional namespaces can be added to the statically known namespaces by namespace declarations, schema imports, or module imports in a Prolog, by a module declaration, and by namespace declaration attributes in direct element constructors.

  • [Definition: Default namespace for elements and types. This is either a namespace URI, or the special value "##any", or absentDM. This indicates how unprefixed QNames are interpreted when they appear in a position where an element name or type name is expected.]

    • If the value is set to a namespace URI, this namespace is used for any such unprefixed QName. The URI value is whitespace-normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2.

    • The special value "##any" indicates that:

      • When an unprefixed QName is used as a name test for selecting named elements in an axis step, the name test will match an element having the specified local name, in any namespace or none.

      • When an unprefixed QName is used in a context where a type name is expected (but not as a function name), the default namespace is the xs namespace, http://www.w3.org/2001/XMLSchema.

      • In any other context, an unprefixed QName represents a name in no namespace.

    • If the value is absentDM, an unprefixed QName representing an element or type name is interpreted as being in no namespace.

  • [Definition: Default function namespace. This is either a namespace URI, or absentDM. The namespace URI, if present, is used for any unprefixed QName appearing in a position where a function name is expected.] The URI value is whitespace-normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2

    In its simplest form its value is simply a whitespace-normalized xs:anyURI value (most commonly, the URI http://www.w3.org/2005/xpath-functions) to be used as the default namespace for unprefixed function names. However, the use of a more complex algorithm is not precluded, for example an algorithm which searches multiple namespaces for a matching name.

    In XQuery, a default function namespace can be declared in the prolog in a default function namespace declaration (see 5.14 Default Namespace Declaration); in the absence of such a declaration, the namespace http://www.w3.org/2005/xpath-functions is used.

  • [Definition: In-scope schema definitions is a generic term for all the element declarations, attribute declarations, and schema type definitions that are in scope during static analysis of an expression.] It includes the following three parts:

  • [Definition: In-scope variables. This is a mapping from expanded QName to type. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.]

    Variable declarations in a Prolog are added to in-scope variables. An expression that binds a variable extends the in-scope variables, within the scope of the variable, with the variable and its type. Within the body of an inline function expression or user-defined function, the in-scope variables are extended by the names and types of the function parameters.

    The static type of a variable may either be declared in a query or inferred by static type inference as discussed in 2.3.3.1 Static Analysis Phase.

  • [Definition: In-scope named item types. This is a mapping from expanded QName to named item types.]

    [Definition: A named item type is an ItemType identified by an expanded QName.]

    Named item types serve two purposes:

    • They allow frequently used item types, especially complex item types such as record types, to be given simple names, to avoid repeating the definition every time it is used.

    • They allow the definition of recursive types, which are useful for describing recursive data structures such as lists and trees. For details see 3.2.8.4 Recursive Record Types.

    Note:

    In XQuery, named item types can be declared in the Query Prolog.

  • [Definition: Statically known function definitions. This is a set of function definitions.]

    Function definitions are described in 2.2.1.1 Function Definitions.

  • [Definition: Statically known collations. This is an implementation-defined mapping from URI to collation. It defines the names of the collations that are available for use in processing queries and expressions.] [Definition: A collation is a specification of the manner in which strings and URIs are compared and, by extension, ordered. For a more complete definition of collation, see Section 5.3 Comparison of stringsFO.]

  • [Definition: Construction mode. The construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xs:untyped; all element nodes copied during node construction receive the type xs:untyped, and all attribute nodes copied during node construction receive the type xs:untypedAtomic.]

  • [Definition: Default order for empty sequences. This component controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression, as described in 4.13.9 Order By Clause.] Its value may be greatest or least.

  • [Definition: Boundary-space policy. This component controls the processing of boundary whitespace by direct element constructors, as described in 4.12.1.4 Boundary Whitespace.] Its value may be preserve or strip.

  • [Definition: Copy-namespaces mode. This component controls the namespace bindings that are assigned when an existing element node is copied by an element constructor, as described in 4.12.1 Direct Element Constructors. Its value consists of two parts: preserve or no-preserve, and inherit or no-inherit.]

  • [Definition: Static Base URI. This is an absolute URI, used to resolve relative URIs during static analysis. ] For example, it is used to resolve module location URIs in XQuery, and the URIs in xsl:import and xsl:include in XSLT. All expressions within a module have the same static base URI. The Static Base URI can be set using a base URI declaration.

    Relative URI references are resolved as described in 2.5.6 Resolving a Relative URI Reference.

    At execution time, relative URIs supplied to functions such as fn:doc are resolved against the Executable Base URI, which may or may not be the same as the Static Base URI.

  • [Definition: Statically known decimal formats. This is a mapping from QNames to decimal formats, with one default format that has no visible name, referred to as the unnamed decimal format. Each format is available for use when formatting numbers using the fn:format-number function.]

    Decimal formats are described in 2.2.1.2 Decimal Formats.

2.2.1.1 Function Definitions

[Definition: A function definition contains information used to evaluate a static function call, including the name, parameters, and return type of the function.]

The properties of a function definition include:

  • The function name, which is an expanded QName.

  • Parameter definitions, specifically:

    The names of the parameters must be distinct.

    [Definition: A function definition has an arity range, which is a range of consecutive non-negative integers. If the function definition has M required parameters and N optional parameters, then its arity range is from M to M+N inclusive.]

    The static context may contain several function definitions with the same name, but the arity ranges of two such function definitions must not overlap. For example, if two function definitions A and B have the same function name, then:

    • It is acceptable for A to have two required parameters and no optional parameters, while B has three required parameters and one optional parameter.

    • It is not acceptable for A to have one required parameter while B has three optional parameters.

    Note:

    Implementations must ensure that no two function definitions have the same expanded QName and overlapping arity ranges (even if the signatures are consistent).

    XQuery and XSLT enforce this rule by defining a static error if the rule is violated; but further constraints may be needed if an API allows external functions to be added to the static context.

  • A return type (a sequence type)

  • The function category, which is one of application, system, or external:

    • [Definition: Application functions are function definitions written in a host language such as XQuery or XSLT whose syntax and semantics are defined in this family of specifications. Their behavior (including the rules determining the static and dynamic context) follows the rules for such functions in the relevant host language specification.] The most common application functions are functions written by users in XQuery or XSLT.

    • [Definition: System functions include the functions defined in [XQuery and XPath Functions and Operators 4.0], functions defined by the specifications of a host language, constructor functions for atomic types, and any additional functions provided by the implementation. System functions are sometimes called built-in functions.]

      The behavior of system functions follows the rules given for the individual function in this family of specifications, or in the specification of the particular processor implementation. A system function may have behavior that depends on the static or dynamic context of the caller (for example, comparing strings using the default collation from the dynamic context of the caller). Such functions are said to be context dependent.

    • [Definition: External functions can be characterized as functions that are neither part of the processor implementation, nor written in a language whose semantics are under the control of this family of specifications. The semantics of external functions, including any context dependencies, are entirely implementation-defined. In XSLT, external functions are called Section 24.1 Extension Functions XT30. ]

      For example, an implementation might provide a mechanism allowing external functions to be written in a language such as Java or Python. The way in which argument and return values are converted between the XDM type system and the type system of the external language is implementation-defined.

    [Definition: A function definition is said to be context dependent if its result depends on the static or dynamic context of its caller. A function definition may be context-dependent for some arities in its arity range, and context-independent for others: for example fn:name#0 is context-dependent while fn:name#1 is context-independent.]

    Note:

    Some system functions, such as fn:position, fn:last, and fn:static-base-uri, exist for the sole purpose of providing information about the static or dynamic context of their caller.

    Note:

    Application functions are context dependent only to the extent that they define optional parameters with default values that are context dependent.

  • A (possibly empty) set of function annotations

    In XQuery, function annotations are described in 5.15 Annotations.

  • A body. The function body contains the logic that enables the function result to be computed from the supplied arguments and information in the static and dynamic context.

The function definitions present in the static context are available for reference from a static function call, or from a named function reference.

2.2.1.2 Decimal Formats

Changes in 4.0  

  1. Several decimal format properties, including minus sign, exponent separator, percent, and per-mille, can now be rendered as arbitrary strings rather than being confined to a single character.   [Issue 1048 PR 1250 3 June 2024]

Each decimal format defines a set of properties, which control the interpretation of characters in the picture string supplied to the fn:format-number function, and also specify characters to be used in the result of formatting the number.

Each property potentially has two parts: a marker character M used in the picture string to mark an insertion position, and a rendition string R to indicate how the relevant property is to be rendered in the output of the fn:format-number function. In the list below properties are annotated with (M), (R), or (M, R) to indicate whether the property includes a marker character, a rendition string, or both.

In XQuery and XSLT declarations defining the values of properties, a property where the marker character and the rendition differ is indicated using the syntax M:R. For example the percent property may be expressed as %:pc to indicate that the character % will be used in the picture string, and the string pc will be used in the function output. In this example, the value 0.10, formatted with the picture string #0%, results in the output 10pc

  • [Definition: decimal-separator(M, R) is used to separate the integer part of the number from the fractional part. The default value for both the marker and the rendition is U+002E (FULL STOP, PERIOD, .) .]

  • [Definition: exponent-separator(M, R) is used to separate the mantissa from the exponent in scientific notation. The default value for both the marker and the rendition is U+0065 (LATIN SMALL LETTER E, e) .]

  • [Definition: grouping-separator(M, R) is used to separate groups of digits (for example as a thousands separator). The default value for both the marker and the rendition is U+002C (COMMA, ,) .]

  • [Definition: percent(M, R) is used to indicate that the number is written as a per-hundred fraction; the default value for both the marker and the rendition is U+0025 (PERCENT SIGN, %) .]

  • [Definition: per-mille(M, R) is used to indicate that the number is written as a per-thousand fraction; the default value for both the marker and the rendition is U+2030 (PER MILLE SIGN, ) .]

  • [Definition: zero-digit(M) is the character used in the picture string to represent the digit zero; the default value is U+0030 (DIGIT ZERO, 0) . This character must be a digit (category Nd in the Unicode property database), and it must have the numeric value zero. This property implicitly defines the ten Unicode characters that are used to represent the values 0 to 9 in the function output: Unicode is organized so that each set of decimal digits forms a contiguous block of characters in numerical sequence. Within the picture string any of these ten character can be used (interchangeably) as a place-holder for a mandatory digit. Within the final result string, these ten characters are used to represent the digits zero to nine.]

  • [Definition: digit(M) is a character used in the picture string to represent an optional digit; the default value is U+0023 (NUMBER SIGN, #) .]

  • [Definition: pattern-separator(M) is a character used to separate positive and negative sub-pictures in a picture string; the default value is U+003B (SEMICOLON, ;) .]

  • [Definition: infinity(R) is the string used to represent the double value infinity (INF); the default value is the string "Infinity" ]

  • [Definition: NaN(R) is the string used to represent the double value NaN (not a number); the default value is the string "NaN" ]

  • [Definition: minus-sign(R) is the string used to mark negative numbers; the default value is U+002D (HYPHEN-MINUS, -) .]

2.2.2 Dynamic Context

Changes in 4.0  

  1. The concept of the context item has been generalized, so it is now a context value. That is, it is no longer constrained to be a single item.   [Issue 129 PR 368 14 September 2023]

  2. The rules regarding the document-uri property of nodes returned by the fn:collection function have been relaxed.   [Issue 1161 PR 1265 11 June 2024]

[Definition: The dynamic context of an expression is defined as information that is needed for the dynamic evaluation of an expression, beyond any information that is needed from the static context.] If evaluation of an expression relies on some part of the dynamic context that is absentDM, a type error is raised [err:XPDY0002].

Note:

In previous versions of the specification, this was classified as a dynamic error. The change allows the error to be raised during static analysis when possible; for example a function written as fn($x) { @code } can now be reported as an error whether or not the function is actually evaluated. The actual error code remains unchanged for backwards compatibility reasons.

There are other cases where static detection of the error is not possible.

The individual components of the dynamic context are described below.

In general, the dynamic context for the outermost expression is supplied externally, often by some kind of application programming interface (API) allowing XQuery 4.0 expressions to be invoked from a host language. Application Programming Interfaces are outside the scope of this specification. In XQuery 4.0, some aspects of the dynamic context (for example, initial values of variables) are defined within the query prolog. The dynamic context for inner subexpressions may be set by their containing expressions: for example in a mapping expression E1!E2, the value of the focus (part of the dynamic context) for evaluation of E2 is defined by the evaluation of E1.

Some aspects of the dynamic context are outside the direct control of the query author; they are defined by the implementation, which may or may not allow them to be configured by users. An example is available documents, which is an abstraction for the set of XML documents that can be retrieved by URI from within an expression. In some environments this may be the entire contents of the web; in others it may be constrained to documents that satisfy particular security constraints; and in some environments the set of available documents might even be empty. These components of the dynamic context are generally treated as being constant for the duration of the execution.

Rules governing the initialization and alteration of these components can be found in C.2 Dynamic Context Components.

The components of the dynamic context are listed below.

[Definition: The first three components of the dynamic context (context value, context position, and context size) are called the focus of the expression. ] The focus enables the processor to keep track of which items are being processed by the expression. If any component in the focus is defined, all components of the focus are defined.

[Definition: A fixed focus is a focus for an expression that is evaluated once, rather than being applied to a series of values; in a fixed focus, the context value is set to one specific value, the context position is 1, and the context size is 1.]

[Definition: A singleton focus is a fixed focus in which the context value is a singleton item.]. With a singleton focus, the context value is a single item, the context position is 1, and the context size is 1.

Certain language constructs, notably the path operatorE1/E2, the simple map operatorE1!E2, and the predicateE1[E2], create a new focus for the evaluation of a sub-expression. In these constructs, E2 is evaluated once for each item in the sequence that results from evaluating E1. Each time E2 is evaluated, it is evaluated with a different focus. The focus for evaluating E2 is referred to below as the inner focus, while the focus for evaluating E1 is referred to as the outer focus. The inner focus is used only for the evaluation of E2. Evaluation of E1 continues with its original focus unchanged.

  • [Definition: The context value is the value currently being processed.] In many cases (but not always), the context value will be a single item. [Definition: When the context value is a single item, it can also be referred to as the context item; when it is a single node, it can also be referred to as the context node.] The context value is returned by an expression consisting of a single dot (.). When an expression E1/E2 or E1[E2] is evaluated, each item in the sequence obtained by evaluating E1 becomes the context value in the inner focus for an evaluation of E2.

    [Definition: In the dynamic context of every module in a query, the context value component must have the same setting. If this shared setting is not absentDM, it is referred to as the initial context value. ]

  • [Definition: The context position is the position of the context value within the series of values currently being processed.] It changes whenever the context value changes. When the focus is defined, the value of the context position is an integer greater than zero. The context position is returned by the expression fn:position(). When an expression E1/E2 or E1[E2] is evaluated, the context position in the inner focus for an evaluation of E2 is the position of the context value in the sequence obtained by evaluating E1. The position of the first item in a sequence is always 1 (one). The context position is always less than or equal to the context size.

  • [Definition: The context size is the number of values in the series of values currently being processed.] Its value is always an integer greater than zero. The context size is returned by the expression fn:last(). When an expression E1/E2 or E1[E2] is evaluated, the context size in the inner focus for an evaluation of E2 is the number of items in the sequence obtained by evaluating E1.

  • [Definition: Variable values. This is a mapping from expanded QName to value. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.]

  • [Definition: Dynamically known function definitions. This is a set of function definitions. It includes the statically known function definitions as a subset, but may include other function definitions that are not known statically. ]

    The function definitions in the dynamic context are used primarily by the fn:function-lookup function.

    If two function definitions in the dynamically known function definitions have the same name, then their arity ranges must not overlap.

    Note:

    The reason for allowing named functions to be available dynamically beyond those that are available statically is primarily to allow for cases where the run-time execution environment is significantly different from the compile-time environment. This could happen, for example, if a stylesheet or query is compiled within a web server and then executed in the web browser. The fn:function-lookup function allows dynamic discovery of resources that were not available statically.

  • [Definition: Current dateTime. This information represents an implementation-dependent point in time during the processing of a query , and includes an explicit timezone. It can be retrieved by the fn:current-dateTime function. If called multiple times during the execution of a query , this function always returns the same result.]

  • [Definition: Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or arithmetic operation. The implicit timezone is an implementation-defined value of type xs:dayTimeDuration. See Section 3.2.7.3 Timezones XS1-2 or Section 3.3.7 dateTime XS11-2 for the range of valid values of a timezone.]

  • [Definition: Executable Base URI. This is an absolute URI used to resolve relative URIs during the evaluation of expressions; it is used, for example, to resolve a relative URI supplied to the fn:doc or fn:unparsed-text functions. ]

    URIs are resolved as described in 2.5.6 Resolving a Relative URI Reference.

    The function fn:static-base-uri, despite its name, returns the value of the Executable Base URI.

    In many straightforward processing scenarios, the Executable Base URI in the dynamic context will be the same as the Static Base URI for the corresponding expression in the static context. There are situations, however, where they may differ:

    • Some processors may allow the static analysis of a query or stylesheet to take place on a development machine, while execution of the query or stylesheet happens on a test or production server. In this situation, resources needed during static analysis (such as other modules of the query or stylesheet) will be located on the development machine, by reference to the Static Base URI, while resources needed during execution (such as reference data files) will be located on the production machine, accessed via the Executable Base URI.

    • When the fn:static-base-uri function is called within the initializing expression of an optional parameter in a function declaration, it returns the executable base URI of the relevant function call. This allows a user-written function to accept two parameters: a required parameter containing a relative URI, and an optional parameter containing a base URI. The optional parameter can be given a default value of fn:static-base-uri(), allowing the code in the function body to resolve the relative URI against the executable base URI of the caller.

  • [Definition: Default collation. This identifies one of the collations in statically known collations as the collation to be used by functions and operators for comparing and ordering values of type xs:string and xs:anyURI (and types derived from them) when no explicit collation is specified.]

    Note:

    Although the default collation is defined (in 4.0) as a property of the dynamic context, its value will in nearly all cases be known statically. The reason it is defined in the dynamic context is to allow a call on the fn:default-collation function to be used when defining the default value of an optional parameter to a user-defined function. In this situation, the actual value supplied for the parameter is taken from the dynamic context of the relevant function call.

  • [Definition: Default language. This is the natural language used when creating human-readable output (for example, by the functions fn:format-date and fn:format-integer) if no other language is requested. The value is a language code as defined by the type xs:language.]

  • [Definition: Default calendar. This is the calendar used when formatting dates in human-readable output (for example, by the functions fn:format-date and fn:format-dateTime) if no other calendar is requested. The value is a string.]

  • [Definition: Default place. This is a geographical location used to identify the place where events happened (or will happen) when processing dates and times using functions such as fn:format-date, fn:format-dateTime, and fn:civil-timezone, if no other place is specified. It is used when translating timezone offsets to civil timezone names, and when using calendars where the translation from ISO dates/times to a local representation is dependent on geographical location. Possible representations of this information are an ISO country code or an Olson timezone name, but implementations are free to use other representations from which the above information can be derived. The only requirement is that it should uniquely identify a civil timezone, which means that country codes for countries with multiple timezones, such as the United States, are inadequate.]

  • [Definition: Available documents. This is a mapping of strings to document nodes. Each string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.] The set of available documents may be empty.

  • [Definition: Available text resources. This is a mapping of strings to text resources. Each string represents the absolute URI of a resource. The resource is returned by the fn:unparsed-text function when applied to that URI.] The set of available text resources may be empty.

  • [Definition: Available collections. This is a mapping of strings to sequences of items. Each string represents the absolute URI of a resource. The sequence of items represents the result of the fn:collection function when that URI is supplied as the argument. ] The set of available collections may be empty.

    Ideally, for every document node D that is in the target of a mapping in available item collections, or that is the root of a tree containing such a node, the document-uri property of D should either be absent, or should be a URI U such that available documents contains a mapping from U to D.

    Note:

    That is to say, the document-uri property of nodes returned by the fn:collection function should be such that calling fn:doc with that URI returns the relevant node.

    It is not always possible to ensure this, especially in cases where dereferencing of document or collection URIs is configurable using configuration files or user-supplied resolver code.

  • [Definition: Default collection. This is the sequence of items that would result from calling the fn:collection function with no arguments.] The value of default collection may be initialized by the implementation.

  • [Definition: Available URI collections. This is a mapping of strings to sequences of URIs. The string represents the absolute URI of a resource which can be interpreted as an aggregation of a number of individual resources each of which has its own URI. The sequence of URIs represents the result of the fn:uri-collection function when that URI is supplied as the argument. ] There is no implication that the URIs in this sequence can be successfully dereferenced, or that the resources they refer to have any particular media type.

    Note:

    An implementation may maintain some consistent relationship between the available collections and the available URI collections, for example by ensuring that the result of fn:uri-collection(X)!fn:doc(.) is the same as the result of fn:collection(X). However, this is not required. The fn:uri-collection function is more general than fn:collection in that fn:collection allows access to nodes that might lack individual URIs, for example nodes corresponding to XML fragments stored in the rows of a relational database.

  • [Definition: Default URI collection. This is the sequence of URIs that would result from calling the fn:uri-collection function with no arguments.] The value of default URI collection may be initialized by the implementation.

  • [Definition: Environment variables. This is a mapping from names to values. Both the names and the values are strings. The names are compared using an implementation-defined collation, and are unique under this collation. The set of environment variables is implementation-defined and may be empty.]

    Note:

    A possible implementation is to provide the set of POSIX environment variables (or their equivalent on other operating systems) appropriate to the process in which the query is initiated .

2.3 Processing Model

Changes in 4.0  

  1. The static typing option has been dropped.   [Issue 1343 PR 1344 3 September 2024]

The semantics of XQuery 4.0 are defined in terms of the data model and the expression context.

Processing                          Model Overview

Figure 1: Processing Model Overview

Figure 1 provides a schematic overview of the processing steps that are discussed in detail below. Some of these steps are completely outside the domain of XQuery 4.0; in Figure 1, these are depicted outside the line that represents the boundaries of the language, an area labeled external processing. The external processing domain includes generation of XDM instances that represent the data to be queried (see 2.3.1 Data Model Generation), schema import processing (see 2.3.2 Schema Import Processing), and serialization (see 2.3.5 Serialization). The area inside the boundaries of the language is known as the query processing domain, which includes the static analysis and dynamic evaluation phases (see 2.3.3 Expression Processing). Consistency constraints on the query processing domain are defined in 2.3.6 Consistency Constraints.

2.3.1 Data Model Generation

The input data for a query must be represented as one or more XDM instances. This process occurs outside the domain of XQuery 4.0, which is why Figure 1 represents it in the external processing domain.

In many cases the input data might originate as XML. Here are some steps by which an XML document might be converted to an XDM instance:

  1. A document may be parsed using an XML parser that generates an XML Information Set (see [XML Infoset]). The parsed document may then be validated against one or more schemas. This process, which is described in [XML Schema 1.0 Part 1] or [XML Schema 1.1 Part 1], results in an abstract information structure called the Post-Schema Validation Infoset (PSVI). If a document has no associated schema, its Information Set is preserved. (See DM1 in Figure 1)

  2. The Information Set or PSVI may be transformed into an XDM instance by a process described in [XQuery and XPath Data Model (XDM) 4.0]. (See DM2 in Figure 1)

The above steps provide an example of how an XDM instance might be constructed. An XDM instance might also be constructed in some other way (see DM3 in Figure 1), for example it might be synthesized directly from a relational database, or derived by parsing a JSON text or a CSV file. Whatever the origin, XQuery 4.0 is defined in terms of the data model, but it does not place any constraints on how XDM instances are constructed.

The remainder of this section is concerned with the common case where XML data is being processed.

[Definition: Each element node and attribute node in an XDM instance has a type annotation (described in Section 2.8 Schema InformationDM). The type annotation of a node is a reference to a schema type. ] The type-name of a node is the name of the type referenced by its type annotation (but note that the type annotation can be a reference to an anonymous type). If the XDM instance was derived from a validated XML document as described in Section 3.3 Construction from a PSVIDM, the type annotations of the element and attribute nodes are derived from schema validation. XQuery 4.0 does not provide a way to directly access the type annotation of an element or attribute node.

The value of an attribute is represented directly within the attribute node. An attribute node whose type is unknown (such as might occur in a schemaless document) is given the type annotationxs:untypedAtomic.

The value of an element is represented by the children of the element node, which may include text nodes and other element nodes. The type annotation of an element node indicates how the values in its child text nodes are to be interpreted. An element that has not been validated (such as might occur in a schemaless document) is annotated with the schema typexs:untyped. An element that has been validated and found to be partially valid is annotated with the schema type xs:anyType. If an element node is annotated as xs:untyped, all its descendant element nodes are also annotated as xs:untyped. However, if an element node is annotated as xs:anyType, some of its descendant element nodes may have a more specific type annotation.

2.3.2 Schema Import Processing

The in-scope schema definitions in the static context may be extracted from actual XML schemas (see step SI1 in Figure 1) or may be generated by some other mechanism (see step SI2 in Figure 1). In either case, the result must satisfy the consistency constraints defined in 2.3.6 Consistency Constraints.

2.3.3 Expression Processing

XQuery 4.0 defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Figure 1). During the static analysis phase, static errors, dynamic errors, or type errors may be raised. During the dynamic evaluation phase, only dynamic errors or type errors may be raised. These kinds of errors are defined in 2.4.1 Kinds of Errors.

Within each phase, an implementation is free to use any strategy or algorithm whose result conforms to the specifications in this document.

2.3.3.1 Static Analysis Phase

[Definition: The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).]

During the static analysis phase, the query is typically parsed into an internal representation called the operation tree (step SQ1 in Figure 1). A parse error is raised as a static error [err:XPST0003]. The static context is initialized by the implementation (step SQ2). The static context is then changed and augmented based on information in the prolog (step SQ3). If the Schema Aware Feature is supported, the in-scope schema definitions are populated with information from imported schemas. If the Module Feature is supported, the static context is extended with function declarations and variable declarations from imported modules. The static context is used to resolve schema type names, function names, namespace prefixes, and variable names (step SQ4). If a name of one of these kinds in the operation tree is not found in the static context, a static error ([err:XPST0008] or [err:XPST0017]) is raised (however, see exceptions to this rule in 3.2.7.2 Element Test and 3.2.7.4 Attribute Test.)

The operation tree is then typically normalized by making explicit the implicit operations such as atomization and extraction of effective boolean values (step SQ5).

During the static analysis phase, a processor may perform type analysis. The effect of type analysis is to assign a static type to each expression in the operation tree. [Definition: The static type of an expression is the best inference that the processor is able to make statically about the type of the result of the expression.] This specification does not define the rules for type analysis nor the static types that are assigned to particular expressions: the only constraint is that the inferred type must match all possible values that the expression is capable of returning.

Examples of inferred static types might be:

  • For the expression concat(a,b) the inferred static type is xs:string

  • For the expression $a = $v the inferred static type is xs:boolean

  • For the expression $s[exp] the inferred static type has the same item type as the static type of $s, but a cardinality that allows the empty sequence even if the static type of $s does not allow an empty sequence.

  • The inferred static type of the expression data($x) (whether written explicitly or inserted into the operation tree in places where atomization is implicit) depends on the inferred static type of $x: for example, if $x has type element(*, xs:integer) then data($x) has static type xs:integer.

In XQuery 1.0 and XPath 2.0, rules for static type inferencing were published normatively in [XQuery 1.0 and XPath 2.0 Formal Semantics], but implementations were allowed to refine these rules to infer a more precise type where possible. In subsequent versions, the rules for static type inferencing are entirely implementation-dependent.

Every kind of expression also imposes requirements on the type of its operands. For example, with the expression substring($a, $b, $c), $a must be of type xs:string (or something that can be converted to xs:string by the function calling rules), while $b and $c must be numeric.

A processor may raise a type error during static analysis if the inferred static type of an expression has no overlap (intersection) with the required type, and cannot be converted to the required type using the coercion rules. For example, given the call fn:upper-case($s), the processor may raise an error if the declared or inferred type of $s is xs:integer, but not if it is xs:anyAtomicType.

In addition, type analysis may conclude that an expression is implausible. Implausible expressions may be considered erroneous unless such checks have been disabled. This topic is described further in 2.4.6 Implausible Expressions.

Alternatively, the processor may defer all type checking until the dynamic evaluation phase.

2.3.3.2 Dynamic Evaluation Phase

[Definition: The dynamic evaluation phase is the phase during which the value of an expression is computed.] It is dependent on successful completion of the static analysis phase.

The dynamic evaluation phase can occur only if no errors were detected during the static analysis phase.

The dynamic evaluation phase depends on the operation tree of the expression being evaluated (step DQ1), on the input data (step DQ4), and on the dynamic context (step DQ5), which in turn draws information from the external environment (step DQ3) and the static context (step DQ2). The dynamic evaluation phase may create new data-model values (step DQ4) and it may extend the dynamic context (step DQ5)—for example, by binding values to variables.

[Definition: Every value matches one or more sequence types. A value is said to have a dynamic typeT if it matches (or is an instance of) the sequence type T.]

In many cases (but not all), one of the dynamic types that a value matches will be a subtype of all the others, in which case it makes sense to speak of “the dynamic type” of the value as meaning this single most specific type. In other cases (examples are empty maps and empty arrays) none of the dynamic types is more specific than all the others.

Note:

An atomic item has a type annotation which will always be a subtype of all the other types that it matches; we can therefore refer to this as the dynamic type of the atomic item without ambiguity.

A value may match a dynamic type that is more specific than the static type of the expression that computed it (for example, the static type of an expression might be xs:integer*, denoting a sequence of zero or more integers, but at evaluation time its value may be an instance of xs:integer, denoting exactly one integer).

If an operand of an expression does not have a dynamic type that is a subtype of the static type required for that operand, a type error is raised [err:XPTY0004].

Even though static typing can catch many type errors before an expression is executed, it is possible for an expression to raise an error during evaluation that was not detected by static analysis. For example, an expression may contain a cast of a string into an integer, which is statically valid. However, if the actual value of the string at run time cannot be cast into an integer, a dynamic error will result. Similarly, an expression may apply an arithmetic operator to a value whose static type is xs:untypedAtomic. This is not a static error, but at run time, if the value cannot be successfully cast to a numeric type, a dynamic error will be raised.

2.3.4 Input Sources

XQuery 4.0 has a set of functions that provide access to XML documents (fn:doc, fn:doc-available), collections (fn:collection, fn:uri-collection), text files (fn:unparsed-text, fn:unparsed-text-lines, fn:unparsed-text-available), and environment variables (fn:environment-variable, fn:available-environment-variables). These functions are defined in Section 13.6 Functions giving access to external informationFO.

An expression can access input data either by calling one of these input functions or by referencing some part of the dynamic context that is initialized by the external environment, such as a variable or context value.

Note:

The EXPath Community Group has developed a File Module, which some implementations use to perform file system related operations such as reading or writing files and directories. Multiple files can be read or written from a single query.

2.3.5 Serialization

[Definition: Serialization is the process of converting an XDM instance to a sequence of octets (step DM4 in Figure 1.), as described in [XSLT and XQuery Serialization 4.0].]

Although serialization of XQuery results is outside the scope of this specification, syntax is provided in the query prolog to enable default serialization options to be defined. See 5.22 Output Declarations.

Serialization can also be invoked from within a query by calling the fn:serialize function.

Note:

This definition of serialization is the definition used in this specification. Any form of serialization that is not based on [XSLT and XQuery Serialization 4.0] is outside the scope of the XQuery 4.0 specification.

An XQuery implementation is not required to provide a serialization interface. For example, an implementation may provide only a DOM interface (see [Document Object Model]) or an interface based on an event stream.

2.3.6 Consistency Constraints

In order for XQuery 4.0 to be well defined, the input XDM instances, the static context, and the dynamic context must be mutually consistent. The consistency constraints listed below are prerequisites for correct functioning of an XQuery 4.0 implementation. Enforcement of these consistency constraints is beyond the scope of this specification. This specification does not define the result of a query under any condition in which one or more of these constraints is not satisfied.

  • For every node that has a type annotation, if that type annotation is found in the in-scope schema definitions (ISSD), then its definition in the ISSD must be compatibleDM with its definition in the schemaDM that was used to validate the node.

  • Every element name, attribute name, or schema type name referenced in in-scope variables or statically known function definitions must be in the in-scope schema definitions, unless it is an element name referenced as part of an ElementTest or an attribute name referenced as part of an AttributeTest.

  • Any reference to a global element, attribute, or type name in the in-scope schema definitions must have a corresponding element, attribute or type definition in the in-scope schema definitions.

  • For each (variable, type) pair in in-scope variables and the corresponding (variable, value) pair in variable values such that the variable names are equal, the value must match the type, using the matching rules in 3.1.2 Sequence Type Matching.

  • For each variable declared as external, if the variable declaration does not include a VarDefaultValue, the external environment must provide a value for the variable.

    For each variable declared as external for which the external environment provides a value: If the variable declaration includes a declared type, the value provided by the external environment must match the declared type, using the matching rules in 3.1.2 Sequence Type Matching. If the variable declaration does not include a declared type, the external environment must provide a type to accompany the value provided, using the same matching rules.

  • For each function declared as external: the function’s implementation must either return a value that matches the declared result type, using the matching rules in 3.1.2 Sequence Type Matching, or raise an implementation-defined error.

  • For a given query, define a participating ISSD as the in-scope schema definitions of a module that is used in evaluating the query. All participating ISSDs must be compatibleDM.

    Note:

    This rule ensures that when one module M imports schema X, and another module N imports schema Y, then an element node validated against type T in M can be safely passed to a function in N that expects an argument of type element(*, T). The requirement for compatibility does not guarantee that in all cases, validation of an element against the two different schemas will produce exactly the same outcome (there may be differences, for example, in the definition of substitution groups or wildcards), and the processor must allow for such differences.

  • In the statically known namespaces, the prefix xml must not be bound to any namespace URI other than http://www.w3.org/XML/1998/namespace, and no prefix other than xml may be bound to this namespace URI. The prefix xmlns must not be bound to any namespace URI, and no prefix may be bound to the namespace URI http://www.w3.org/2000/xmlns/.

2.4 Error Handling

2.4.1 Kinds of Errors

As described in 2.3.3 Expression Processing, XQuery 4.0 defines a static analysis phase, which does not depend on input data, and a dynamic evaluation phase, which does depend on input data. Errors may be raised during each phase.

[Definition: An error that can be detected during the static analysis phase, and is not a type error, is a static error.] A syntax error is an example of a static error.

[Definition: A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase.] Numeric overflow is an example of a dynamic error.

[Definition: A type error may be raised during the static analysis phase or the dynamic evaluation phase. During the static analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the dynamic evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.]

The outcome of the static analysis phase is either success or one or more type errors, static errors, or statically detected dynamic errors. The result of the dynamic evaluation phase is either a result value, a type error, or a dynamic error.

If more than one error is present, or if an error condition comes within the scope of more than one error defined in this specification, then any non-empty subset of these errors may be reported.

If an implementation can determine during the static analysis phase that a QueryBody , if evaluated, would necessarily raise a dynamic error or that an expression, if evaluated, would necessarily raise a type error, the implementation may (but is not required to) report that error during the static analysis phase.

An implementation can raise a dynamic error for a QueryBody statically only if the query can never execute without raising that error, as in the following example:

error()

The following example contains a type error, which can be reported statically even if the implementation can not prove that the expression will actually be evaluated.

if (empty($arg))
then "cat" * 2
else 0

[Definition: In addition to static errors, dynamic errors, and type errors, an XQuery 4.0 implementation may raise warnings, either during the static analysis phase or the dynamic evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.]

In addition to the errors defined in this specification, an implementation may raise a dynamic error for a reason beyond the scope of this specification. For example, limitations may exist on the maximum numbers or sizes of various objects. An error must be raised if such a limitation is exceeded [err:XPDY0130].

2.4.2 Identifying and Reporting Errors

The errors defined in this specification are identified by QNames that have the form err:XXYYnnnn, where:

  • err denotes the namespace for XPath and XQuery errors, http://www.w3.org/2005/xqt-errors. This binding of the namespace prefix err is used for convenience in this document, and is not normative.

  • XX denotes the language in which the error is defined, using the following encoding:

    • XP denotes an error defined by XPath. Such an error may also occur XQuery since XQuery includes XPath as a subset.

    • XQ denotes an error defined by XQuery (or an error originally defined by XQuery and later added to XPath).

  • YY denotes the error category, using the following encoding:

    • ST denotes a static error.

    • DY denotes a dynamic error.

    • TY denotes a type error.

  • nnnn is a unique numeric code.

Note:

The namespace URI for XPath and XQuery errors is not expected to change from one version of XQuery to another. However, the contents of this namespace may be extended to include additional error definitions.

The method by which an XQuery 4.0 processor reports error information to the external environment is implementation-defined.

An error can be represented by a URI reference that is derived from the error QName as follows: an error with namespace URI NS and local part LP can be represented as the URI reference NS#LP. For example, an error whose QName is err:XPST0017 could be represented as http://www.w3.org/2005/xqt-errors#XPST0017.

Note:

Along with a code identifying an error, implementations may wish to return additional information, such as the location of the error or the processing phase in which it was detected. If an implementation chooses to do so, then the mechanism that it uses to return this information is implementation-defined.

2.4.3 Handling Dynamic Errors

Except as noted in this document, if any operand of an expression raises a dynamic error, the expression also raises a dynamic error. If an expression can validly return a value or raise a dynamic error, the implementation may choose to return the value or raise the dynamic error (see 2.4.4 Errors and Optimization). For example, the logical expression expr1 and expr2 may return the value false if either operand returns false, or may raise a dynamic error if either operand raises a dynamic error.

If more than one operand of an expression raises an error, the implementation may choose which error is raised by the expression. For example, in this expression:

($x div $y) + xs:decimal($z)

both the sub-expressions ($x div $y) and xs:decimal($z) may raise an error. The implementation may choose which error is raised by the + expression. Once one operand raises an error, the implementation is not required, but is permitted, to evaluate any other operands.

[Definition: In addition to its identifying QName, a dynamic error may also carry a descriptive string and one or more additional values called error values.] An implementation may provide a mechanism whereby an application-defined error handler can process error values and produce diagnostic messages. XQuery 3.1 provides standard error handling via Section 4.20 Try/Catch ExpressionsXQ.

A dynamic error may be raised by a system function or operator. For example, the div operator raises an error if its operands are xs:decimal values and its second operand is equal to zero. Errors raised by system functions and operators are defined in [XQuery and XPath Functions and Operators 4.0] or the host language.

A dynamic error can also be raised explicitly by calling the fn:error function, which always raises a dynamic error and never returns a value. This function is defined in Section 3.1.1 fn:errorFO. For example, the following function call raises a dynamic error, providing a QName that identifies the error, a descriptive string, and a diagnostic value (assuming that the prefix app is bound to a namespace containing application-defined error codes):

error(xs:QName("app:err057"), "Unexpected value", string($v))

2.4.4 Errors and Optimization

Because different implementations may choose to evaluate or optimize an expression in different ways, certain aspects of raising dynamic errors are implementation-dependent, as described in this section.

An implementation is always free to evaluate the operands of an operator in any order.

In some cases, a processor can determine the result of an expression without accessing all the data that would be implied by the formal expression semantics. For example, the formal description of filter expressions suggests that $s[1] should be evaluated by examining all the items in sequence $s, and selecting all those that satisfy the predicate position()=1. In practice, many implementations will recognize that they can evaluate this expression by taking the first item in the sequence and then exiting. If $s is defined by an expression such as //book[author eq 'Berners-Lee'], then this strategy may avoid a complete scan of a large document and may therefore greatly improve performance. However, a consequence of this strategy is that a dynamic error or type error that would be detected if the expression semantics were followed literally might not be detected at all if the evaluation exits early. In this example, such an error might occur if there is a book element in the input data with more than one author subelement.

The extent to which a processor may optimize its access to data, at the cost of not raising errors, is defined by the following rules.

Consider an expression Q that has an operand (sub-expression) E. In general the value of E is a sequence. At an intermediate stage during evaluation of the sequence, some of its items will be known and others will be unknown. If, at such an intermediate stage of evaluation, a processor is able to establish that there are only two possible outcomes of evaluating Q, namely the value V or an error, then the processor may deliver the result V without evaluating further items in the operand E. For this purpose, two values are considered to represent the same outcome if their items are pairwise the same, where nodes are the same if they have the same identity, and values are the same if they are equal and have exactly the same type.

There is an exception to this rule: If a processor evaluates an operand E (wholly or in part), then it is required to establish that the actual value of the operand E does not violate any constraints on its cardinality. For example, the expression $e eq 0 results in a type error if the value of $e contains two or more items. A processor is not allowed to decide, after evaluating the first item in the value of $e and finding it equal to zero, that the only possible outcomes are the value true or a type error caused by the cardinality violation. It must establish that the value of $e contains no more than one item.

These rules apply to all the operands of an expression considered in combination: thus if an expression has two operands E1 and E2, it may be evaluated using any samples of the respective sequences that satisfy the above rules.

The rules cascade: if A is an operand of B and B is an operand of C, then the processor needs to evaluate only a sufficient sample of B to determine the value of C, and needs to evaluate only a sufficient sample of A to determine this sample of B.

The effect of these rules is that the processor is free to stop examining further items in a sequence as soon as it can establish that further items would not affect the result except possibly by causing an error. For example, the processor may return true as the result of the expression S1 = S2 as soon as it finds a pair of equal values from the two sequences.

Another consequence of these rules is that where none of the items in a sequence contributes to the result of an expression, the processor is not obliged to evaluate any part of the sequence. Again, however, the processor cannot dispense with a required cardinality check: if an empty sequence is not permitted in the relevant context, then the processor must ensure that the operand is not an empty sequence.

Examples:

  • If an implementation can find (for example, by using an index) that at least one item returned by $expr1 in the following example has the value 47, it is allowed to return true as the result of the some expression, without searching for another item returned by $expr1 that would raise an error if it were evaluated.

    some $x in $expr1 satisfies $x = 47
  • In the following example, if an implementation can find (for example, by using an index) the product element-nodes that have an id child with the value 47, it is allowed to return these nodes as the result of the path expression, without searching for another product node that would raise an error because it has an id child whose value is not an integer.

    //product[id = 47]

For a variety of reasons, including optimization, implementations may rewrite expressions into a different form. There are a number of rules that limit the extent of this freedom:

  • Other than the raising or not raising of errors, the result of evaluating a rewritten expression must conform to the semantics defined in this specification for the original expression.

    Note:

    This allows an implementation to return a result in cases where the original expression would have raised an error, or to raise an error in cases where the original expression would have returned a result. The main cases where this is likely to arise in practice are (a) where a rewrite changes the order of evaluation, such that a subexpression causing an error is evaluated when the expression is written one way and is not evaluated when the expression is written a different way, and (b) where intermediate results of the evaluation cause overflow or other out-of-range conditions.

    Note:

    This rule does not mean that the result of the expression will always be the same in non-error cases as if it had not been rewritten, because there are many cases where the result of an expression is to some degree implementation-dependent or implementation-defined.

  • The rules described in 2.4.5 Guarded Expressions ensure that for certain kinds of expression (for example conditional expressions), changing the order of evaluation of subexpressions does not result in dynamic errors that would not otherwise occur.

  • Expressions must not be rewritten in such a way as to create or remove static errors. The static errors in this specification are defined for the original expression, and must be preserved if the expression is rewritten.

  • As stated earlier, an expression must not be rewritten to dispense with a required cardinality check: for example, string-length(//title) must raise an error if the document contains more than one title element.

2.4.5 Guarded Expressions

Changes in 4.0  

  1. The rules for “errors and optimization” have been tightened up to disallow many cases of optimizations that alter error behavior. In particular there are restrictions on reordering the operands of and and or, and of predicates in filter expressions, in a way that might allow the processor to raise dynamic errors that the author intended to prevent.   [Issue 71 PR 230 15 November 2022]

[Definition: An expression E is said to be guarded by some governing condition C if evaluation of E is not allowed to fail with a dynamic error except when C applies.]

For example, in a conditional expression if (P) then T else F, the subexpression T is guarded by P, and the subexpression F is guarded by not(P). One way an implementation can satisfy this rule is by not evaluating T unless P is true, and likewise not evaluating F unless P is false. Another way of satisfying the rule is for the implementation to evaluate all the subexpressions, but to catch any errors that occur in a guarded subexpression so they are not propagated.

The existence of this rule enables errors to be prevented by writing expressions such as if ($y eq 0) then "N/A" else ($x div $y). This example will never fail with a divide-by-zero error because the else branch of the conditional is guarded.

Similarly, in the mapping expression E1!E2, the subexpression E2 is guarded by the existence of an item from E1. This means, for example, that the expression (1 to $n)!doc('bad.xml') must not raise a dynamic error if $n is zero. The rule governing evaluation of guarded expressions is phrased so as not to disallow “loop-lifting” or “constant-folding” optimizations whose aim is to avoid repeated evaluation of a common subexpression; but such optimizations must not result in errors that would not otherwise occur.

The complete list of expressions that have guarded subexpressions is as follows:

  • In a conditional expression (IfExpr) the then branch is guarded by the condition being true, and the else branch is guarded by the condition being false.

  • In a switch expression (SwitchExpr), the return expression of a particular case is guarded by the condition for that case matching, and no earlier case matching.

  • In a typeswitch expression (TypeswitchExpr), the return expression of a particular case is guarded by the condition for that case matching, and no earlier case matching.

  • In an and expression (AndExpr), the second operand is guarded by the value of the first operand being true.

  • In an or expression (OrExpr), the second operand is guarded by the value of the first operand being false.

  • In an otherwise expression (OtherwiseExpr), the second operand is guarded by the value of the first operand being an empty sequence.

  • In a path expression of the form E1/E2 or E1//E2, and in a mapping expression of the form E1!E2, the right-hand operand E2 is guarded by the existence of at least one item in the result of evaluating E1.

    This rule applies even if E2 does not reference the context value. For example, no dynamic error can be thrown by the expression (1 to $n)!doc('bad.xml') in the case where $n is zero.

  • In a filter expression of the form E[P], the predicate P is guarded by the existence of at least one item in the result of evaluating E.

    This rule has the consequence that in a filter expression with multiple predicates, such as E[P1][P2], evaluation of P2 must not raise a dynamic error unless P1 returns true. This rule does not prevent reordering of predicates (for example, to take advantage of indexes), but it does require that any such reordering must not result in errors that would not otherwise occur.

  • In a FLWOR expression (FLWORExpr), an expression that is logically dependent on the tuples in the tuple stream is guarded by the existence of a relevant tuple. This applies even where the expression does not actually reference any of the variable bindings in the tuple stream. For example, in the expression for $x in S return E, the expression E is guarded by the existence of an item bound to $x.

    This means that the expression for $x in 1 to $n return doc('bad.xml') must not raise a dynamic error in the case where $n is zero.

  • In a quantified expression (QuantifiedExpr) such as some $x in S satisfies P, the expression P is guarded by the existence of an item bound to $x.

The fact that an expression is guarded does not remove the obligation to report static errors in the expression; nor does it remove the option to report statically detectable type errors.

Note:

These rules do not constrain the order of evaluation of subexpressions. For example, given an expression such as //person[@first = "Winston"][@last = "Churchill"], or equivalently //person[@first = "Winston" and @last = "Churchill"], an implementation might use an index on the value of @last to select items that satisfy the second condition, and then filter these items on the value of the first condition. Alternatively, it might evaluate both predicates in parallel. Or it might interpose an additional redundant condition: //person[string-length(@first) + string-length(@last) = 16][@first = "Winston"][@last = "Churchill"]. But implementations must ensure that such rewrites do not result in dynamic errors being reported that would not occur if the predicates were evaluated in order as written.

Note:

Although the rules for guarded expressions prevent optimizations resulting in spurious errors, they do not prevent optimizations whose effect is to mask errors. For example, the rules guarantee that ("A", 3)[. instance of xs:integer][. eq 3] will not raise an error caused by the comparison ("A" eq 3), but they do not guarantee the converse: the expression ("A", 3)[. eq 3][. instance of xs:integer] may or may not raise a dynamic error.

Note:

The rules in this section do not disallow all expression rewrites that might result in dynamic errors. For example, rewriting ($x - $y + $z) as ($x + $z - $y) is permitted even though it might result in an arithmetic overflow.

Note:

Some implementations allow calls on external functions that have side-effects. The semantics of such function calls are entirely implementation defined. Processors may choose to reference the rules for guarded expressions when defining the behavior of such function calls, but this is outside the scope of the language specification.

2.4.6 Implausible Expressions

Changes in 4.0  

  1. The rules for reporting type errors during static analysis have been changed so that a processor has more freedom to report errors in respect of constructs that are evidently wrong, such as @price/@value, even though dynamic evaluation is defined to return an empty sequence rather than an error.   [Issue 602 PR 603 25 July 2023]

[Definition: Certain expressions, while not erroneous, are classified as being implausible, because they achieve no useful effect.]

An example of an implausible expression is @code/text(). This expression will always evaluate to an empty sequence, because attribute nodes cannot have text node children. The semantics of the expression are well defined, but it is likely that the user writing this expression intended something different; if they wanted to an expression that evaluated to an empty sequence, there would be easier ways to write it.

Where an expression is classified (by rules in this specification) as being implausible, a processor may (but is not required to) raise a static error.

For reasons of backwards compatibility and interoperability, and to facilitate automatic generation of XQuery 4.0 code, a processor must provide a mode of operation in which implausible expressions are not treated as static errors, but are evaluated with the defined semantics for the expression.

Some other examples of implausible expressions include:

  • round(tokenize($input)). The result of fn:tokenize is a sequence of strings (xs:string*), while the required type for the first argument of fn:round is optional numeric (xs:numeric?). The expression can succeed only in the exceptional case where the result of fn:tokenize is an empty sequence, in which case the result of fn:round will also be an empty sequence; it is therefore highly likely that the expression was written in error.

  • parse-csv($input)?column-names. The signature of the parse-csv function declares its return type as record(columns, rows). There is no field in this record named column-names, and therefore the lookup expression will always return an empty sequence. Again, there is no good reason that a user would write this, so it is likely that it was written in error.

Note:

The specification is deliberately conservative in the choice of constructs that have been classified as implausible. Constructs have not been classified as implausible merely because there are better ways of writing the same thing, but only in cases where it is considered that no user in full understanding of the specification would intentionally write such a construct. All these cases correspond to situations that would be classed as errors in a language with stricter static typing rules.

Note:

In many cases the classification of constructs as implausible is designed to protect users from usability problems that have been found with earlier versions of the language. without introducing backwards incompatibilities.

2.5 Concepts

This section explains some concepts that are important to the processing of XQuery 4.0 expressions.

2.5.1 Document Order

An ordering called document order is defined among all the nodes accessible during processing of a given query , which may consist of one or more trees (documents or fragments). Document order is defined in Section 2.5 Document OrderDM, and its definition is repeated here for convenience. Document order is a total ordering, although the relative order of some nodes is implementation-dependent. [Definition: Informally, document order is the order in which nodes appear in the XML serialization of a document.] [Definition: Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query , even if this order is implementation-dependent.] [Definition: The node ordering that is the reverse of document order is called reverse document order.]

Within a tree, document order satisfies the following constraints:

  1. The root node is the first node.

  2. Every node occurs before all of its children and descendants.

  3. Attribute nodes immediately follow the element node with which they are associated. The relative order of attribute nodes is stable but implementation-dependent.

  4. The relative order of siblings is the order in which they occur in the children property of their parent node.

  5. Children and descendants occur before following siblings.

The relative order of nodes in distinct trees is stable but implementation-dependent, subject to the following constraint: If any node in a given tree T1 is before any node in a different tree T2, then all nodes in tree T1 are before all nodes in tree T2.

2.5.2 Typed Value and String Value

Every node has a typed value and a string value, except for nodes whose value is absentDM. [Definition: The typed value of a node is a sequence of atomic items and can be extracted by applying the Section 2.1.4 fn:dataFO function to the node.] [Definition: The string value of a node is a string and can be extracted by applying the Section 2.1.3 fn:stringFO function to the node.]

An implementation may store both the typed value and the string value of a node, or it may store only one of these and derive the other as needed. The string value of a node must be a valid lexical representation of the typed value of the node, but the node is not required to preserve the string representation from the original source document. For example, if the typed value of a node is the xs:integer value 30, its string value might be "30" or "0030".

The typed value, string value, and type annotation of a node are closely related, and are defined by rules found in the following locations:

The relationship between typed value and string value for various kinds of nodes is summarized and illustrated by examples below.

  1. For text and document nodes, the typed value of the node is the same as its string value, as an instance of the type xs:untypedAtomic. The string value of a document node is formed by concatenating the string values of all its descendant text nodes, in document order.

  2. The typed value of a comment or processing instruction node is the same as its string value. It is an instance of the type xs:string.

  3. The typed value of an attribute node with the type annotationxs:anySimpleType or xs:untypedAtomic is the same as its string value, as an instance of xs:untypedAtomic. The typed value of an attribute node with any other type annotation is derived from its string value and type annotation using the lexical-to-value-space mapping defined in [XML Schema 1.0] or [XML Schema 1.1] Part 2 for the relevant type.

    Example: A1 is an attribute having string value "3.14E-2" and type annotation xs:double. The typed value of A1 is the xs:double value whose lexical representation is 3.14E-2.

    Example: A2 is an attribute with type annotation xs:IDREFS, which is a list datatype whose item type is the atomic datatype xs:IDREF. Its string value is "bar baz faz". The typed value of A2 is a sequence of three atomic items ("bar", "baz"", "faz""), each of type xs:IDREF. The typed value of a node is never treated as an instance of a named list type. Instead, if the type annotation of a node is a list type (such as xs:IDREFS), its typed value is treated as a sequence of the generalized atomic type from which it is derived (such as xs:IDREF).

  4. For an element node, the relationship between typed value and string value depends on the node’s type annotation, as follows:

    1. If the type annotation is xs:untyped or xs:anySimpleType or denotes a complex type with mixed content (including xs:anyType), then the typed value of the node is equal to its string value, as an instance of xs:untypedAtomic. However, if the nilled property of the node is true, then its typed value is the empty sequence.

      Example: E1 is an element node having type annotation xs:untyped and string value "1999-05-31". The typed value of E1 is "1999-05-31", as an instance of xs:untypedAtomic.

      Example: E2 is an element node with the type annotation formula, which is a complex type with mixed content. The content of E2 consists of the character H, a child element named subscript with string value "2", and the character O. The typed value of E2 is "H2O" as an instance of xs:untypedAtomic.

    2. If the type annotation denotes a simple type or a complex type with simple content, then the typed value of the node is derived from its string value and its type annotation in a way that is consistent with schema validation. However, if the nilled property of the node is true, then its typed value is the empty sequence.

      Example: E3 is an element node with the type annotation cost, which is a complex type that has several attributes and a simple content type of xs:decimal. The string value of E3 is "74.95". The typed value of E3 is 74.95, as an instance of xs:decimal.

      Example: E4 is an element node with the type annotation hatsizelist, which is a simple type derived from the atomic typehatsize, which in turn is derived from xs:integer. The string value of E4 is "7 8 9". The typed value of E4 is a sequence of three values (7, 8, 9), each of type hatsize.

      Example: E5 is an element node with the type annotation my:integer-or-string which is a union type with member types xs:integer and xs:string. The string value of E5 is "47". The typed value of E5 is 47 as a xs:integer, since xs:integer is the member type that validated the content of E5. In general, when the type annotation of a node is a union type, the typed value of the node will be an instance of one of the member types of the union.

      Note:

      If an implementation stores only the string value of a node, and the type annotation of the node is a union type, the implementation must be able to deliver the typed value of the node as an instance of the appropriate member type.

    3. If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence and its string value is the zero-length string.

    4. If the type annotation denotes a complex type with element-only content, then the typed value of the node is absentDM. The fn:data function raises a type error [err:FOTY0012]FO40 when applied to such a node. The string value of such a node is equal to the concatenated string values of all its text node descendants, in document order.

      Example: E6 is an element node with the type annotation weather, which is a complex type whose content type specifies element-only. E6 has two child elements named temperature and precipitation. The typed value of E6 is absentDM, and the fn:data function applied to E6 raises an error.

2.5.3 Atomization

The semantics of some XQuery 4.0 operators depend on a process called atomization. Atomization is applied to a value when the value is used in a context in which a sequence of atomic items is required. The result of atomization is either a sequence of atomic items or a type error [err:FOTY0012]FO40. [Definition: Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.1.4 fn:dataFO.]

The semantics of fn:data are repeated here for convenience. The result of fn:data is the sequence of atomic items produced by applying the following rules to each item in the input sequence:

  • If the item is an atomic item, it is returned.

  • If the item is a node, its typed value is returned (a type error [err:FOTY0012]FO40 is raised if the node has no typed value.)

  • If the item is a function item (other than an array) or map a type error [err:FOTY0013]FO40 is raised.

  • If the item is an array $a, atomization is defined as $a?* ! fn:data(.), which is equivalent to atomizing the members of the array.

    Note:

    This definition recursively atomizes members that are arrays. Hence, the result of atomizing the array [ [ 1, 2, 3 ], [ 4, 5, 6 ] ] is the sequence (1, 2, 3, 4, 5, 6).

Atomization is used in processing the following types of expressions:

  • Arithmetic expressions

  • Comparison expressions

  • Function calls and returns

  • Cast expressions

  • Constructor expressions for various kinds of nodes

  • order by clauses in FLWOR expressions

  • group by clauses in FLWOR expressions

  • Switch expressions

2.5.4 Effective Boolean Value

Under certain circumstances (listed below), it is necessary to find the effective boolean value of a value. [Definition: The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in Section 7.3.1 fn:booleanFO.]

The dynamic semantics of fn:boolean are repeated here for convenience:

  1. If its operand is an empty sequence, fn:boolean returns false.

  2. If its operand is a sequence whose first item is a node, fn:boolean returns true.

  3. If its operand is a singleton value of type xs:boolean or derived from xs:boolean, fn:boolean returns the value of its operand unchanged.

  4. If its operand is a singleton value of type xs:string, xs:anyURI, xs:untypedAtomic, or a type derived from one of these, fn:boolean returns false if the operand value has zero length; otherwise it returns true.

  5. If its operand is a singleton value of any numeric type or derived from a numeric type, fn:boolean returns false if the operand value is NaN or is numerically equal to zero; otherwise it returns true.

  6. In all other cases, fn:boolean raises a type error [err:FORG0006]FO40.

    Note:

    For instance, fn:boolean raises a type error if the operand is a function, a map, or an array.

The effective boolean value of a sequence is computed implicitly during processing of the following types of expressions:

Note:

The definition of effective boolean value is not used when casting a value to the type xs:boolean, for example in a cast expression or when passing a value to a function whose expected parameter is of type xs:boolean.

2.5.5 URI Literals

XQuery 4.0 requires a statically known, valid URI in a URILiteral or a BracedURILiteral. An implementation may raise a static error [err:XQST0046] if the value of a URI Literal or a Braced URI Literal is of nonzero length and is neither an absolute URI nor a relative URI.

As in a string literal, any predefined entity reference (such as &amp;), character reference (such as &#x2022;), or EscapeQuot or EscapeApos (for example, "") is replaced by its appropriate expansion. Certain characters, notably the ampersand, can only be represented using a predefined entity reference or a character reference.

Note:

The xs:anyURI type is designed to anticipate the introduction of Internationalized Resource Identifiers (IRIs) as defined in [RFC3987].

Whitespace is normalized using the whitespace normalization rules of fn:normalize-space. If the result of whitespace normalization contains only whitespace, the corresponding URI consists of the empty string. Whitespace normalization is done after the expansion of character references, so writing a newline (for example) as &#xA; does not prevent its being normalized to a space character.

A Braced URI Literal or URI Literal is not subjected to percent-encoding or decoding as defined in [RFC3986].

2.5.6 Resolving a Relative URI Reference

[Definition: To resolve a relative URI$rel against a base URI $base is to expand it to an absolute URI, as if by calling the function fn:resolve-uri($rel, $base).] During static analysis, the base URI is the Static Base URI. During dynamic evaluation, the base URI used to resolve a relative URI reference depends on the semantics of the expression.

Any process that attempts to resolve a URI against a base URI, or to dereference the URI, may apply percent-encoding or decoding as defined in the relevant RFCs.

3 Types

As noted in 2.1.2 Values, every value in XQuery 4.0 is regarded as a sequence of zero, one, or more items. The type system of XQuery 4.0, described in this section, classifies the kinds of value that the language can handle, and the operations permitted on different kinds of value.

The type system of XQuery 4.0 is related to the type system of [XML Schema 1.0] or [XML Schema 1.1] in two ways:

This chapter of the specification starts by defining sequence types and item types, which describe the range of values that can be bound to variables, used in expressions, or passed to functions. It then describes how these relate to schema types, that is, the simple and complex types defined in an XSD schema.

3.1 Sequence Types

[Definition: A sequence type is a type that can be expressed using the SequenceType syntax. Sequence types are used whenever it is necessary to refer to a type in an XQuery 4.0 expression. The term sequence type suggests that this syntax is used to describe the type of an XQuery 4.0 value, which is always a sequence.]

[Definition: An item type is a type that can be expressed using the ItemType syntax, which forms part of the SequenceType syntax. Item types match individual items.] In most cases, the set of items matched by an item type consists either exclusively of atomic items, exclusively of nodes, or exclusively of function itemsDM. Exceptions include the generic types item(), which matches all items, xs:error, which matches no items, and choice item types, which can match any combination of types.

Whenever it is necessary to refer to a type in an XQuery 4.0 expression, the SequenceType syntax is used.

SequenceType::=("empty-sequence" "(" ")")
| (ItemTypeOccurrenceIndicator?)
ItemType::=AnyItemTest | TypeName | KindTest | FunctionType | MapType | ArrayType | RecordType | EnumerationType | ChoiceItemType
OccurrenceIndicator::="?" | "*" | "+"
/* xgc: occurrence-indicators */

In many situations the terms item type and sequence type are used interchangeably to refer either to the type itself, or to the syntactic construct that designates the type: so in the expression $x instance of xs:string*, the construct xs:string* uses the SequenceType syntax to designate a sequence type whose instances are sequences of strings. When more precision is required, the specification is careful to use the terms item type and sequence type to refer to the actual types, while using the production names ItemType and SequenceType to refer to the syntactic designators of these types.

[Definition: A sequence type designator is a syntactic construct conforming to the grammar rule SequenceType. A sequence type designator is said to designate a sequence type.]

[Definition: An item type designator is a syntactic construct conforming to the grammar rule ItemType. An item type designator is said to designate an item type.]

Note:

Two item type designators may designate the same item type. For example, element() and element(*) are equivalent, as are attribute(A) and attribute(A, xs:anySimpleType).

With the exception of the special type empty-sequence(), a sequence type consists of an item type that constrains the type of each item in the sequence, and a cardinality that constrains the number of items in the sequence. Apart from the item type item(), which permits any kind of item, item types divide into node types (such as element()), generalized atomic types (such as xs:integer) and function types (such as function() as item()*).

Lexical QNames appearing in a sequence type have their prefixes expanded to namespace URIs by means of the statically known namespaces and (where applicable) the default namespace for elements and types. Equality of QNames is defined by the eq operator.

Item types representing element and attribute nodes may specify the required type annotations of those nodes in the form of a schema type. Thus the item type element(*, us:address) denotes any element node whose type annotation is (or is derived from) the schema type named us:address.

The occurrence indicators +, *, and ? bind to the last ItemType in the SequenceType, as described in the occurrence-indicators constraint.

3.1.1 Examples of Sequence Types

Here are some examples of sequence types that might be used in XQuery 4.0:

  • xs:date refers to the built-in atomic schema type named xs:date

  • attribute()? refers to an optional attribute node

  • element() refers to any element node

  • element(po:shipto, po:address) refers to an element node that has the name po:shipto and has the type annotation po:address (or a schema type derived from po:address)

  • element(*, po:address) refers to an element node of any name that has the type annotation po:address (or a type derived from po:address)

  • element(customer) refers to an element node named customer with any type annotation

  • schema-element(customer) refers to an element node whose name is customer (or is in the substitution group headed by customer) and whose type annotation matches the schema type declared for a customer element in the in-scope element declarations

  • node()* refers to a sequence of zero or more nodes of any kind

  • item()+ refers to a sequence of one or more items

  • function(*) refers to any function item, regardless of arity or type

  • function(node()) as xs:string* refers to a function item that takes a single argument whose value is a single node, and returns a sequence of zero or more xs:string values

  • (fn(node()) as xs:string)* refers to a sequence of zero or more function items, each of which takes a single argument whose value is a single node, and returns as its result a single xs:string value

3.1.2 Sequence Type Matching

[Definition: SequenceType matching compares a value with an expected sequence type. ] For example, an instance of expression returns true if a given value matches a given sequence type, and false if it does not.

An XQuery 4.0 implementation must be able to determine relationships among the types in type annotations in an XDM instance and the types in the in-scope schema definitions (ISSD). An XQuery 4.0 implementation must be able to determine relationships among the types in ISSDs used in different modules of the same query.

[Definition: The use of a value that has a dynamic type that is a subtype of the expected type is known as subtype substitution.] Subtype substitution does not change the actual type of a value. For example, if an xs:integer value is used where an xs:decimal value is expected, the value retains its type as xs:integer.

The definition of SequenceType matching relies on a pseudo-function named derives-from(AT, ET), which takes an actual simple or complex schema type AT and an expected simple or complex schema type ET, and either returns a boolean value or raises a type error [err:XPTY0004]. This function is defined as follows:

  • derives-from(AT, ET) raises a type error [err:XPTY0004] if ET is not present in the in-scope schema definitions (ISSD).

  • derives-from(AT, ET) returns true if any of the following conditions applies:

    • AT is ET

    • ET is the base type of AT

    • ET is a pure union type of which AT is a member type

    • There is a type MT such that derives-from(AT, MT) and derives-from(MT, ET)

  • Otherwise, derives-from(AT, ET) returns false

The rules for SequenceType matching are given below, with examples (the examples are for purposes of illustration, and do not cover all possible cases).

An OccurrenceIndicator specifies the number of items in a sequence, as follows:

  • ? matches zero or one items

  • * matches zero or more items

  • + matches one or more items

As a consequence of these rules, any sequence type whose OccurrenceIndicator is * or ? matches a value that is an empty sequence.

3.2 Item Types

ItemType::=AnyItemTest | TypeName | KindTest | FunctionType | MapType | ArrayType | RecordType | EnumerationType | ChoiceItemType
AnyItemTest::="item" "(" ")"
TypeName::=EQName
KindTest::=DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
DocumentTest::="document-node" "(" (ElementTest | SchemaElementTest | NameTestUnion)? ")"
ElementTest::="element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
SchemaElementTest::="schema-element" "(" ElementName ")"
AttributeTest::="attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
SchemaAttributeTest::="schema-attribute" "(" AttributeName ")"
ElementName::=EQName
AttributeName::=EQName
PITest::="processing-instruction" "(" (NCName | StringLiteral)? ")"
CommentTest::="comment" "(" ")"
NamespaceNodeTest::="namespace-node" "(" ")"
TextTest::="text" "(" ")"
AnyKindTest::="node" "(" ")"
FunctionType::=Annotation* (AnyFunctionType
| TypedFunctionType)
AnyFunctionType::=("function" | "fn") "(" "*" ")"
TypedFunctionType::=("function" | "fn") "(" (SequenceType ** ",") ")" "as" SequenceType
ChoiceItemType::="(" (ItemType ++ "|") ")"
MapType::=AnyMapType | TypedMapType
RecordType::=AnyRecordType | TypedRecordType
ArrayType::=AnyArrayType | TypedArrayType
EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"

This section defines the syntax and semantics of different ItemTypes in terms of the values that they match.

Note:

For an explanation of the EBNF grammar notation (and in particular, the operators ++ and **), see A.1 EBNF.

An item type designator written simply as an EQName (that is, a TypeName) is interpreted as follows:

  1. If the name is written as a lexical QName, then it is expanded using the in-scope namespaces in the static context. If the name is an unprefixed NCName, then it is expanded according to the default namespace for elements and types.

  2. If the name matches a named item type in the static context, then it is taken as a reference to the corresponding item type. The rules that apply are the rules for the expanded item type definition.

  3. Otherwise, it must match the name of a type in the in-scope schema types in the static context: specifically, an atomic type or a pure union type. See 3.5 Schema Types for details.

    Note:

    A name in the xs namespace will always fall into this category, since the namespace is reserved. See 2.1.3 Namespaces and QNames.

  4. If the name cannot be resolved to a type, a static error is raised [err:XPST0051].

3.2.1 General item types

  • item() matches any single item.

    For example, item() matches the atomic item 1, the element <a/>, or the function fn:concat#3.

  • A ChoiceItemType lists a number of alternative item types in parentheses, separated by "|". An item matches a ChoiceItemType it if matches any of the alternatives.

    For example, (map(*) | array(*)) matches any item that is a map or an array.

    Note:

    If there is only one alternative, the ChoiceItemType designates the same item type as the ItemType that is in parentheses. A singleton choice (that is, a parenthesized item type) is used primarily when defining nested item types in a function signature. For example, a sequence of functions that each return a single boolean might be denoted (fn() as xs:boolean)*. In this example the parentheses are needed to indicate where the occurrence indicator belongs.

3.2.2 Atomic Types

Atomic types in the XQuery 4.0 type system correspond directly to atomic types as defined in the [XML Schema 1.0] or [XML Schema 1.1] type system.

Atomic types are either built-in atomic types such as xs:integer, or user-defined atomic types imported from a schema. Atomic types are identified by a QName: see 2.1.3 Namespaces and QNames.

Note:

A schema may also include anonymous atomic types. Such types are not usable directly in XQuery 4.0, though they may appear as the values of type annotations on nodes.

[Definition: A generalized atomic type is an item type whose instances are all atomic items. Generalized atomic types include (a) atomic types, either built-in (for example xs:integer) or imported from a schema, (b) pure union types, either built-in (xs:numeric and xs:error) or imported from a schema, (c) choice item types if their alternatives are all generalized atomic types, and (d) enumeration types. ].

A generalized atomic type may be designated by an ItemType in any of the following ways:

An atomic item A matches the generalized atomic typeGAT if the type annotation of A (call it T) satisfies the condition derives-from(T, GAT).

Example: The ItemTypexs:decimal matches any value of type xs:decimal. It also matches any value of type shoesize, if shoesize is an atomic type derived by restriction from xs:decimal.

Example: Suppose ItemTypedress-size is a union type that allows either xs:decimal values for numeric sizes (for example: 4, 6, 10, 12), or one of an enumerated set of xs:strings (for example: small, medium, large). The ItemTypedress-size matches any of these values.

Note:

The names of list types such as xs:IDREFS are not accepted in this context, but can often be replaced by a generalized atomic type with an occurrence indicator, such as xs:IDREF+.

3.2.3 Union Types

Union types, as defined in XSD, are a variety of simple types. The membership of a union type in XSD may include list types as well as atomic types and other union types.

[Definition: A pure union type is a simple type that satisfies the following constraints: (a) {variety} is union, (b) the {facets} property is empty, (c) no type in the transitive membership of the union type has {variety}list, and (d) no type in the transitive membership of the union type is a type with {variety}union having a non-empty {facets} property].

Note:

The definition of pure union type excludes union types derived by non-trivial restriction from other union types, as well as union types that include list types in their membership. Pure union types have the property that every instance of an atomic type defined as one of the member types of the union is also a valid instance of the union type.

Note:

The current (second) edition of XML Schema 1.0 contains an error in respect of the substitutability of a union type by one of its members: it fails to recognize that this is unsafe if the union is derived by restriction from another union.

This problem is fixed in XSD 1.1, but the effect of the resolution is that an atomic item labeled with an atomic type cannot be treated as being substitutable for a union type without explicit validation. This specification therefore allows union types to be used as item types only if they are defined directly as the union of a number of atomic types.

Note:

Local union types (see 3.2.5 Choice Item Types) and enumeration types cannot be used as the target for schema validation.

3.2.4 Namespace-sensitive Types

[Definition: The namespace-sensitive types are xs:QName, xs:NOTATION, types derived by restriction from xs:QName or xs:NOTATION, list types that have a namespace-sensitive item type, and union types with a namespace-sensitive type in their transitive membership.]

It is not possible to preserve the type of a namespace-sensitive value without also preserving the namespace binding that defines the meaning of each namespace prefix used in the value. Therefore, XQuery 4.0 defines some error conditions that occur only with namespace-sensitive values. For instance, casting to a namespace-sensitive type raises a type error [err:FONS0004]FO40 if the namespace bindings for the result cannot be determined.

3.2.5 Choice Item Types

Changes in 4.0  

  1. Choice item types (an item type allowing a set of alternative item types) are introduced.   [Issue 122 PR 1132 9 April 2024]

[Definition: A choice item type defines an item type that is the union of a number of alternatives. For example the type (xs:hexBinary | xs:base64Binary) defines the union of these two primitive atomic types, while the type (map(*) | array(*)) matches any item that is either a map or an array.]

An item matches a ChoiceItemType if it matches any of the alternatives listed within the parentheses.

For example, the type (xs:NCName | enum("")) matches any value that is either an instance of xs:NCName, or a zero-length string. This might be a suitable type for a variable that holds a namespace prefix.

If all the alternatives are generalized atomic types then the choice item type is itself a generalized atomic type, which means, for example, that it can be used as the target of a cast expression.

Note:

A choice item type in which all the alternatives are atomic behaves in most respects like a schema-defined pure union type. However, because it can be defined at the point of use (for example, within a function signature), it may be more convenient than defining the type in an imported schema.

Note:

Choice item types are particularly useful in function signatures, allowing a function to take arguments of a variety of types. If the choice item type is a local union type, then the semantics are identical to using a named union type, but a local union type is more convenient because it does not need to be defined in a schema, and does not require a schema-aware processor.

A local union type can also be used in a cast expression: cast @when as (xs:date | xs:dateTime) allows the attribute @when to be either an xs:date, or an xs:dateTime.

An instance of expression can be used to test whether a value belongs to one of a number of specified types: $x instance of (xs:string | xs:anyURI | xs:untypedAtomic) returns true if $x is an instance of any of these three atomic types, while $x instance of (map(*) | array(*)) tests whether $x is a map or array.

3.2.6 Enumeration Types

Changes in 4.0  

  1. Enumeration types are added as a new kind of ItemType, constraining the value space of strings.  [Issue 688 PR 691 10 October 2023]

[Definition: An EnumerationType accepts a fixed set of string values.]

EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"

An enumeration type has a value space consisting of a set of xs:string values. When matching strings against an enumeration type, strings are always compared using the Unicode codepoint collation.

For example, if an argument of a function declares the required type as enum("red", "green", "blue"), then the string "green" is accepted, while "yellow" is rejected with a type error.

Technically, enumeration types are defined as follows:

  • An enumeration type with a single enumerated value (such as enum("red")) is an anonymous atomic type derived from xs:string by restriction using an enumeration facet that permits only the value "red". This is referred to as a singleton enumeration type. It is equivalent to the XSD-defined type:

    <xs:simpleType>
      <xs:restriction base="xs:string">
        <xs:enumeration value="red"/>
      </xs:restriction>
    </xs:simpleType>
  • Two singleton enumeration types are the same type if and only if they have the same (single) enumerated value, as determined using the Unicode codepoint collation.

  • An enumeration type with multiple enumerated values is a union of singleton enumeration types, so enum("red", "green", "blue") is equivalent to (enum("red") | enum("green") | enum("blue")).

  • In consequence, an enumeration type T is a subtype of an enumeration type U if the enumerated values of T are a subset of the enumerated values of U: see 3.3.2 Subtypes of Item Types.

An enumeration type is thus a generalized atomic type.

It follows from these rules that an atomic item will only satisfy an instance of test if it has the correct type annotation, and this can only be achieved using an explicit cast or constructor function. So the expression "red" instance of enum("red", "green", "blue") returns false. However, the coercion rules ensure that where a variable or function declaration specifies an enumeration type as the required type, a string (or indeed an xs:untypedAtomic or xs:anyURI value) equal to one of the enumerated values will be accepted.

Note:

Some consequences of these rules may not be immediately apparent.

Suppose that an XQuery query contains the declarations:

declare type my:color := enum("red", "green", "orange");
declare type my:fruit := enum("apple", "orange", "banana");
declare variable $orange-color as my:color := "orange";
declare variable $orange-fruit as my:fruit := "orange";

The same applies with the equivalent XSLT syntax:

<xsl:item-type name="my:color" as="enum('red', 'green', 'orange')"/>
<xsl:item-type name="my:fruit" as="enum('apple', 'orange', 'banana')"/>
<xsl:variable name="orange-color" as="my:color" select="'orange'"/>
<xsl:variable name="orange-fruit" as="my:fruit" select="'orange'"/>

Now, the value of $orange-color is an atomic item whose datum is the string "orange", and whose type annotation is the anonymous type designated enum("orange"). Similarly, the value of $orange-fruit is an atomic item whose datum is the string "orange", and whose type annotation is the anonymous type designated enum("orange"). That is, the values of the two variables are indistinguishable and interchangeable in every way. In particular, both values are instances of my:color, and both are instances of my:fruit.

This way of handling enumeration values has advantages and disadvantages. On the positive side, it means that enumeration subsets and supersets work cleanly: a value that is an instance of enum("red", "green", "orange") can be used where an instance of enum("red", "orange", "yellow", "green", "blue", "indigo", "violet") is expected. The downside is that labeling a string as an instance of an enumeration type does not provide type safety: a function that expects an instance of my:color can be called with any string that matches one of the required colors, whether or not it has an appropriate type annotation. A function that expects a color can be successfully called passing a fruit, if they happen to have the same name.

3.2.7 Node Types

Changes in 4.0  

  1. Element and attribute tests can include alternative names: element(chapter|section), attribute(role|class).   [Issue 107 PR 286 17 January 2023]

  2. The NodeTest in an AxisStep now allows alternatives: ancestor::(section|appendix)  [Issue 107 PR 286 17 January 2023]

  3. The syntax document-node(N), where N is a NameTestUnion, is introduced as an abbreviation for document-node(element(N)). For example, document-node(*) matches any well-formed XML document (as distinct from a document fragment).   [Issue 1593  24 November 2024]

Some of the constructs described in this section include a TypeName. This appears as T in:

  • element(N, T)

  • attribute(N, T)

  • document-node(element(N, T))

In these constructs, the type name T is expanded using the in-scope namespaces in the static context, using the default namespace for elements and types if it is unprefixed. The resulting QName must identify a type in the in-scope schema definitions. This can be any schema type: either a simple type, or (except in the case of attributes) a complex type. If it is a simple type then it can be an atomic, union, or list type. It can be a built-in type (such as xs:integer) or a user-defined type. It must however be the name of a type defined in a schema; it cannot be a named item type.

3.2.7.1 Simple Node Tests
  • node() matches any node.

  • text() matches any text node.

  • processing-instruction() matches any processing-instruction node.

  • processing-instruction(N) matches any processing-instruction node whose PITarget is equal to fn:normalize-space(N). If the result of fn:normalize-space(N) is not in the lexical space of NCName, a type error is raised [err:XPTY0004]

    Example: processing-instruction(xml-stylesheet) matches any processing instruction whose PITarget is xml-stylesheet.

    For backward compatibility with XPath 1.0, the PITarget of a processing instruction may also be expressed as a string literal, as in this example: processing-instruction("xml-stylesheet").

    If the specified PITarget is not a syntactically valid NCName, a type error is raised [err:XPTY0004].

  • comment() matches any comment node.

  • namespace-node() matches any namespace node.

  • document-node() matches any document node.

  • document-node(E), where E is an ElementTest or SchemaElementTest (see 3.2.7.2 Element Test and 3.2.7.3 Schema Element Test) matches any document node whose children comprise (in any order) zero or more comment and processing instruction nodes, zero text nodes, and exactly one element node, which itself must match E.

    Example: document-node(element(book)) matches a document node containing exactly one element node that is matched by the ElementTest element(book).

  • The construct document-node(NTU), where NTU is a NameTestUnion, is an abbreviation for document-node(element(NTU)). For example, document-node(*) is an abbreviation for document-node(element(*)), which matches any document node corresponding to a well-formed XML document, that is, one that has one element child, zero or more comment and processing-instruction children, and no text node children.

  • An ItemType that is an ElementTest, SchemaElementTest, AttributeTest, SchemaAttributeTest, or FunctionType matches an item as described in the following sections.

3.2.7.2 Element Test

Changes in 4.0  

  1. Element and attribute tests of the form element(N) and attribute(N) now allow N to be any NameTest, including a wildcard. The forms element(A|B) and attribute(A|B) are also allowed.   [Issue 107 PR 286 17 January 2023]

  2. Setting the default namespace for elements and types to the special value ##any causes an unprefixed element name to act as a wildcard, matching by local name regardless of namespace.

ElementTest::="element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
NameTestUnion::=(NameTest ++ "|")
NameTest::=EQName | Wildcard
Wildcard::="*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
TypeName::=EQName

An ElementTest is used to match an element node by its name and/or type annotation.

An unprefixed EQName within the NameTestUnion is interpreted according to the default namespace for elements and types. The name need not be present in the in-scope element declarations.

If the default namespace for elements and types has the special value ##any, then an unprefixed name N is interpreted as a wildcard *:N.

It is always possible to match no-namespace names explicitly by using the form Q{}N

An unprefixed TypeName is interpreted according to the default namespace for elements and types. The TypeName must be present in the in-scope schema types [err:XPST0008]

If the default namespace for elements and types has the special value ##any, then an unprefixed type name T is interpreted as Q{http://www.w3.org/2001/XMLSchema}T.

Note:

Substitution groups do not affect the semantics of ElementTest.

An ElementTestET matches an item E if the following conditions are satisfied:

  1. E is an element node.

  2. If ET includes a NameTestUnion, then the name of the element node E matches one or more of the NameTests in the NameTestUnion. A name N matches a NameTestNT if one of the following conditions is true:

    1. NT is *

    2. NT is *:local and the local part of N is local.

    3. NT is prefix:* and the namespace URI of N matches the namespace URI bound to prefix in the static context.

    4. NT is BracedURILiteral* and the namespace URI of N matches the namespace URI found in the BracedURILiteral.

    5. NT is an EQName equal to N.

  3. If ET includes a TypeName, then the type annotation of the element node E is either the schema type identified by that type name, or a type derived from that type by restriction.

  4. If E has the nilled property, then ET either includes no TypeName, or includes a TypeName followed by the symbol ?.

Here are some examples of ElementTests:

  1. element() and element(*) match any single element node, regardless of its name or type annotation.

  2. element(person) matches any element node whose name is person, in the default namespace for elements and types.

  3. element(doctor|nurse) matches any element node whose name is doctor or nurse, in the default namespace for elements and types.

  4. element(xhtml:*) matches any element node whose name is in the namespace bound to the prefix xhtml.

  5. element(xhtml:*|svg:*|mathml:*) matches any element node whose name is one of the three namespaces identified, specifically the namespaces bound to the prefixes xhtml, svg, and mathml.

  6. element(Q{http://www.w3.org/2000/svg}*) matches any element node whose name is in the SVG namespace.

  7. element(*:html) matches any element node whose local name is "html", in any namespace.

  8. element(person, surgeon) matches a non-nilled element node whose name is person and whose type annotation is surgeon (or is derived from surgeon).

  9. element(person, surgeon?) matches a nilled or non-nilled element node whose name is person and whose type annotation is surgeon (or is derived from surgeon).

  10. element(*, surgeon) matches any non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

  11. element(*, surgeon?) matches any nilled or non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

Where a TypeName is included in an ElementTestT, and element node will only match the test if it has been validated against a schema that defines type T; furthermore, T must be present in the in-scope schema definitions of the static context of the ElementTest. Although it is guaranteed that type T will have compatibleDM definitions in the schema that was used for validation and in the in-scope schema definitions, it is not guaranteed that revalidation using the in-scope schema definitions would succeed. For example, if substitution group membership varies between the two schemas, the element node may contain children or descendants that the in-scope schema definitions would not allow.

Note:

Technically, element(p|q) is not the same type as the choice item type (element(p)|element(q)). However, (a) they match exactly the same set of element nodes, and (b) each is a subtype of the other, so in practice they are indistinguishable.

3.2.7.3 Schema Element Test
SchemaElementTest::="schema-element" "(" ElementName ")"
ElementName::=EQName

A SchemaElementTest matches an element node against a corresponding element declaration found in the in-scope element declarations.

The ElementName of a SchemaElementTest has its prefixes expanded to a namespace URI by means of the statically known namespaces, or if unprefixed, the is interpreted according to the default namespace for elements and types. If this has the special value "##any", an unprefixed name represents a name in no namespace. If the ElementName specified in the SchemaElementTest is not found in the in-scope element declarations, a static error is raised [err:XPST0008].

A SchemaElementTest matches a candidate element node if all of the following conditions are satisfied:

  1. Either:

    1. The name N of the candidate node matches the specified ElementName, or

    2. The name N of the candidate node matches the name of an element declaration that is a member of the actual substitution group headed by the declaration of element ElementName.

    Note:

    The term “actual substitution group” is defined in [XML Schema 1.1]. The actual substitution group of an element declaration H includes those element declarations P that are declared to have H as their direct or indirect substitution group head, provided that P is not declared as abstract, and that P is validly substitutable for H, which means that there must be no blocking constraints that prevent substitution.

  2. The schema element declaration named N is not abstract.

  3. derives-from( AT, ET ) is true, where AT is the type annotation of the candidate node and ET is the schema type declared in the schema element declaration named N.

  4. If the schema element declaration named N is not nillable, then the nilled property of the candidate node is false.

Example: The SchemaElementTestschema-element(customer) matches a candidate element node in the following two situations:

  1. customer is a top-level element declaration in the in-scope element declarations; the name of the candidate node is customer; the element declaration of customer is not abstract; the type annotation of the candidate node is the same as or derived from the schema type declared in the customer element declaration; and either the candidate node is not nilled, or customer is declared to be nillable.

  2. customer is a top-level element declaration in the in-scope element declarations; the name of the candidate node is client; client is an actual (non-abstract and non-blocked) member of the substitution group of customer; the type annotation of the candidate node is the same as or derived from the schema type declared for the client element; and either the candidate node is not nilled, or client is declared to be nillable.

In the case where the schema X used to validate an element node E (whose name is N) differs from the schema Y represented by the in-scope schema definitions in the static context of the SchemaElementTest, the following considerations apply:

  • In applying the test derives-from( AT, ET ), note that AT will necessarily be present in X, but not necessarily in Y. However, ET will necessarily be present in both; and because the two schemas must be compatibleDM, ET will be the present in both schemas, will have the same definition in both, and will be the declared type of N in both. The test can therefore be applied from knowledge of type AT as defined in schema X.

  • The test as to whether the element name N is a member of the actual substitution group is performed entirely by reference to schema Y. Although the two schemas are compatible, substitution group membership can vary.

3.2.7.4 Attribute Test

Changes in 4.0  

  1. Element and attribute tests of the form element(N) and attribute(N) now allow N to be any NameTest, including a wildcard. The forms element(A|B) and attribute(A|B) are also allowed.   [Issue 107 PR 286 17 January 2023]

AttributeTest::="attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
NameTestUnion::=(NameTest ++ "|")
NameTest::=EQName | Wildcard
Wildcard::="*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
TypeName::=EQName

An AttributeTest is used to match an attribute node by its name and/or type annotation.

An unprefixed EQName within the NameTestUnion refers to a name in no namespace. The name need not be present in the in-scope attribute declarations.

An unprefixed TypeName is interpreted according to the default namespace for elements and types. The TypeName must be present in the in-scope schema types [err:XPST0008]

An AttributeTestAT matches an item A if the following conditions are satisfied:

  1. A is an attribute node.

  2. If AT includes a NameTestUnion, then the name of the attribute node A matches one or more of the NameTests in the NameTestUnion. A name N matches a NameTestNT if one of the following conditions is true:

    1. NT is *

    2. NT is *:local and the local part of N matches local.

    3. NT is prefix:* and the namespace URI of N matches the namespace URI bound to prefix in the static context.

    4. NT is BracedURILiteral* and the namespace URI of N matches the namespace URI found in the BracedURILiteral.

    5. NT is an EQName equal to N.

  3. If AT includes a TypeName, then the type annotation of the attribute node A is either the schema type identified by that type name, or a type derived from that type by restriction.

Here are some examples of AttributeTests:

  • attribute() and attribute(*) match any single attribute node, regardless of its name or type annotation.

  • attribute(price) matches any attribute node whose name is price (in no namespace), regardless of its type annotation.

  • attribute(price|discount) matches any attribute node whose name is price or discount (in no namespace).

  • attribute(xlink:*) matches any attribute node whose name is in the namespace bound to the prefix xlink.

  • element(Q{http://www.w3.org/2000/svg}*) matches any attribute node whose name is in the SVG namespace.

  • attribute(*:default-collation) matches any attribute node whose local name is default-collation, regardless of namespace, and regardless of type annotation.

  • attribute(*:price|*:discount) matches any attribute node whose local name is price or discount, regardless of namespace, and regardless of type annotation.

  • attribute(price, currency) matches an attribute node whose name is price (in no namespace) and whose type annotation is currency (or is derived from currency).

  • attribute(xlink:*, xs:string) matches any attribute node whose name is in the namespace bound to the prefix xlink, and whose type annotation is xs:string or a type derived from xs:string.

  • attribute(*, currency) matches any attribute node whose type annotation is currency (or is derived from currency), regardless of its name.

Unlike the situation with an ElementTest, few problems arise if the attribute was validated using a different schema. This is because simple types can never be derived by extension, and attributes do not have substitution groups.

Note:

Technically, attribute(p|q) is not the same type as the choice item type (attribute(p)|attribute(q)). However, (a) they match exactly the same set of attribute nodes, and (b) each is a subtype of the other, so in practice they are indistinguishable.

3.2.7.5 Schema Attribute Test
SchemaAttributeTest::="schema-attribute" "(" AttributeName ")"
AttributeName::=EQName

A SchemaAttributeTest matches an attribute node against a corresponding attribute declaration found in the in-scope attribute declarations.

The AttributeName of a SchemaAttributeTest has its prefixes expanded to a namespace URI by means of the statically known namespaces. If unprefixed, an AttributeName is in no namespace. If the AttributeName specified in the SchemaAttributeTest is not found in the in-scope attribute declarations, a static error is raised [err:XPST0008].

A SchemaAttributeTest matches a candidate attribute node if both of the following conditions are satisfied:

  1. The name of the candidate node matches the specified AttributeName.

  2. derives-from(AT, ET) is true, where AT is the type annotation of the candidate node and ET is the schema type declared for attribute AttributeName in the in-scope attribute declarations.

Example: The SchemaAttributeTestschema-attribute(color) matches a candidate attribute node if color is a top-level attribute declaration in the in-scope attribute declarations, the name of the candidate node is color, and the type annotation of the candidate node is the same as or derived from the schema type declared for the color attribute.

Unlike the situation with a SchemaElementTest, few problems arise if the attribute was validated using a different schema. This is because attributes do not have substitution groups.

3.2.8 Function, Map, and Array Types

The following sections describe the syntax for item types for functions, including arrays and maps.

The subtype relation among these types is described in the various subsections of 3.3.2 Subtypes of Item Types.

3.2.8.1 Function Type

Changes in 4.0  

  1. The keyword fn is allowed as a synonym for function in function types, to align with changes to inline function declarations.  [Issue 1192 PR 1197 21 May 2024]

  2. The terms FunctionType, ArrayType, MapType, and RecordType replace FunctionTest, ArrayTest, MapTest, and RecordTest, with no change in meaning.

FunctionType::=Annotation* (AnyFunctionType
| TypedFunctionType)
AnyFunctionType::=("function" | "fn") "(" "*" ")"
TypedFunctionType::=("function" | "fn") "(" (SequenceType ** ",") ")" "as" SequenceType

A FunctionType matches selected function items, potentially checking their signatureDM (which includes the types of the arguments and results, and also their annotations, as described in 5.15 Annotations)).

An AnyFunctionType matches any item that is a function.

A TypedFunctionType matches an item if it is a function item and the function’s type signature (as defined in Section 2.9.4 Function ItemsDM) is a subtype of the TypedFunctionType.

Note:

The keywords function and fn are synonymous.

In addition, a TypedFunctionType may match certain maps and arrays, as described in 3.2.8.2 Map Type and 3.2.8.5 Array Type

Here are some examples of FunctionTypes:

  1. function(*) matches any function, including maps and arrays.

    Note:

    This can also be written fn(*).

  2. %my:assertion function(*) matches any function if the implementation-defined function assertion %my:assertion is satisfied.

  3. function(xs:int, xs:int) as xs:int matches any function item with the function signature function(xs:int, xs:int) as xs:int.

    Note:

    This can also be written fn(xs:int, xs:int) as xs:int.

  4. %my:assertion function(xs:int, xs:int) as xs:int matches any function item with the function signature function(xs:int, xs:int) as xs:int if the implementation-defined function assertion %my:assertion is satisfied.

  5. function(xs:anyAtomicType) as item()* matches any map, or any function with the required signature.

  6. function(xs:integer) as item()* matches any array, or any function with the required signature.

[Definition: A function assertion is a predicate that restricts the set of functions matched by a FunctionType. It uses the same syntax as 5.15 Annotations.] XQuery 4.0 does not currently define any function assertions, but future versions may. Other specifications in the XQuery family may also use function assertions in the future.

An unprefixed QName is taken to refer to the namespace http://www.w3.org/2012/xquery. Since this is a reserved namespace, and no assertions are currently defined in this namespace, this means that in practice, use of an unprefixed QName is always an error.

Implementations are free to define their own function assertions, whose behavior is completely implementation-defined. Implementations may also provide a way for users to define their own function assertions.

An implementation may raise implementation-defined errors or warnings for function assertions, for example if the parameters are not correct for a given assertion. If the namespace URI of a function assertion’s expanded QName is not recognized by an implementation, it is ignored, and has no effect on the semantics of the function type.

Note:

An implementation is free to raise warnings for function assertions that it does not recognize.

Note:

Although function assertions use the same syntax as annotations, they are not directly related to annotations. If an implementation defines the annotation blue and uses it in function declarations, there is no guarantee that it will also define a function assertion blue, or that a function assertion named blue matches a function declared with the annotation blue. Of course, an implementation that does so may be more intuitive to users.

Implementations must not define function assertions in reserved namespaces; it is is a static error [err:XQST0045] for a user to define a function assertion in a reserved namespace.

3.2.8.2 Map Type
MapType::=AnyMapType | TypedMapType
AnyMapType::="map" "(" "*" ")"
TypedMapType::="map" "(" ItemType "," SequenceType ")"

The MapTypemap(*) matches any map. The MapTypemap(K, V) matches any map where every key is an instance of K and every value is an instance of V.

Although the grammar for TypedMapType allows the key to be described using the full ItemType syntax, the item type used must be a generalized atomic type. [TODO: error code].

Examples:

Given a map $M whose keys are integers and whose results are strings, such as { 0: "no", 1: "yes" }, consider the results of the following expressions:

  • $M instance of map(*) returns true()

  • $M instance of map(xs:integer, xs:string) returns true()

  • $M instance of map(xs:decimal, xs:anyAtomicType) returns true()

  • not($M instance of map(xs:int, xs:string)) returns true()

  • not($M instance of map(xs:integer, xs:token)) returns true()

A map is also a function item, and therefore matches certain function types. Specifically, a map that matches map(K, V) also matches a function type of the form function(xs:anyAtomicType) as R provided that both the following conditions are satisfied:

Note:

To understand this rule, consider the use of a map $M in a function call $M($K), which is equivalent to the function call map:get($M, $K). This function accepts any atomic item for the argument $K, and hence matches a function type that requires an argument type of xs:anyAtomicType. If the key $K is present in the map, the result of the function will be a value of type V; if not, it will be an empty sequence. The map is therefore substitutable for the function type provided that the function type allows both a value of type V and the empty sequence as possible results.

The key type K does not enter into this rule. That is because in the function call $M($K), the sought key $K does not have to be of the same type as the keys actually present in the map.

The transitivity rules for item type matching mean that if an item M matches a type T, and T is a subtype of U, then M also matches type U. So the fact that a map from integers to strings (map(xs:integer, xs:string)) matches function(xs:anyAtomicType) as xs:string? means that it will also match other function types such as function(xs:integer) as xs:string? and function(xs:decimal) as xs:anyAtomicType?

Furthermore, the rules for function coercion mean that any map can be supplied as a value in a context where it does not actually match the required function type, but can be coerced to a function that does. For example a map of type map(xs:integer, xs:string) can be coerced to a function of type function(xs:integer) as xs:string; in this situation a type error will occur only if a call on the function actually returns an empty sequence.

Examples:

  • $M instance of fn(*) returns true()

  • $M instance of fn(xs:anyAtomicType) as item()* returns true()

  • $M instance of fn(xs:integer) as item()* returns true()

  • $M instance of fn(xs:int) as item()* returns true()

  • $M instance of fn(xs:string) as item()* returns true()

  • not($M instance of fn(xs:integer) as xs:string) returns true()

Note:

The last case might seem surprising; however, function coercion ensures that $M can be used successfully anywhere that the required type is fn(xs:integer) as xs:string.

Rules defining whether one map type is a subtype of another are given in 3.3.2.8 Maps.

3.2.8.3 Record Type

Changes in 4.0  

  1. Record types are added as a new kind of ItemType, constraining the value space of maps.

  2. The syntax record(*) is allowed; it matches any map.   [Issue 52 PR 728 10 October 2023]

  3. The syntax record() is allowed; the only thing it matches is an empty map.   [Issue 1491 ]

RecordType::=AnyRecordType | TypedRecordType
AnyRecordType::="record" "(" "*" ")"
TypedRecordType::="record" "(" (FieldDeclaration ** ",") ExtensibleFlag? ")"
FieldDeclaration::=FieldName "?"? ("as" SequenceType)?
FieldName::=NCName | StringLiteral
ExtensibleFlag::="," "*"

A RecordType matches maps that meet specific criteria.

For example, the RecordTyperecord(r as xs:double, i as xs:double) matches a map if the map has exactly two entries: an entry with key "r" whose value is a singleton xs:double value, and an entry with key "i" whose value is also a singleton xs:double value.

If the list of fields ends with ",*" then the record type is said to be extensible. For example, the RecordTyperecord(e as element(Employee), *) matches a map if it has an entry with key "e" whose value matches element(Employee), regardless what other entries the map might contain.

For generality:

  • The syntax record() defines a record type that has no explicit fields and that is not extensible. The only thing it matches is an empty map.

  • The syntax record(*) defines an extensible record type that has no explicit field declarations. It is equivalent to the item type map(*): that is, it allows any map.

A record type can constrain only those entries whose keys are strings, but when the record type is marked as extensible, then other entries may be present in the map with either string or non-string keys. Entries whose key is a string can be expressed using an (unquoted) NCName if the key conforms to NCName syntax, or using a (quoted) string literal otherwise.

Note:

Lookup expressions have been extended in 4.0 so that non-NCName keys can be used without parentheses: employee?"middle name"

If the type declaration for a field is omitted, then item()* is assumed: that is, the map entry may have any type.

If the field name is followed by a question mark, then the value must have the specified type if it is present, but it may also be absent. For example, the RecordTyperecord(first as xs:string, middle? as xs:string, last as xs:string, *) requires the map to have string-valued entries with keys "first" and "last"; it also declares that if the map has an entry with key "middle", the value of that entry must be a single xs:string. Declaring the type as record(first as xs:string, middle? as xs:string?, last as xs:string, *) also allows the entry with key "middle" to be present but empty.

Note:

Within an extensible record type, a FieldDeclaration that is marked optional and has no declared type does not constrain the map in any way, so it serves no practical purpose, but it is permitted because it may have documentary value.

The names of the fields in a record type must be distinct [err:XPST0021].

Record types describe a subset of the value space of maps. They do not define any new kinds of values, or any additional operations. They are useful in many cases to describe more accurately the type of a variable, function parameter, or function result, giving benefits both in the readability of the code, and in the ability of the processor to detect and diagnose type errors and to optimize execution.

If a variable $rec is known to conform to a particular record type, then when a lookup expression $rec?field is used, (a) the processor can report a type error if $rec cannot contain an entry with name field (see 4.14.3.4 Implausible Lookup Expressions), and (b) the processor can make static type inferences about the type of value returned by $rec?field.

Note:

(TODO: change function signatures as suggested here!) A number of functions in the standard function library use maps as function arguments; this is a useful technique where the information to be supplied across the interface is highly variable. However, the type signature for such functions typically declares the argument type as map(*), which gives very little information (and places very few constraints) on the values that are actually passed across. Using record types offers the possibility of improving this: for example, the options argument of fn:parse-json, previously given as map(*), can now be expressed as record(liberal? as xs:boolean, duplicates? as xs:string, escape? as xs:boolean, fallback as fn(xs:string) as xs:string, *). In principle the xs:string type used to describe the duplicates option could also be replaced by a schema-defined subtype of xs:string that enumerates the permitted values ("reject", "use-first", "use-last").

The use of a record type in the signature of such a function causes the coercion rules to be invoked. So, for example, if the function expects an entry in the map to be an xs:double value, it becomes possible to supply a map in which the corresponding entry has type xs:integer.

Greater precision in defining the types of such arguments also enables better type checking, better diagnostics, better optimization, better documentation, and better syntax-directed editing tools.

Note:

One of the motivations for introducing record types is to enable better pattern matching in XSLT when processing JSON input. With XML input, patterns are often based around XML element names. JSON has no direct equivalent of XML’s element names; matching a JSON object such as {longitude: 130.2, latitude: 53.4} relies instead on recognizing the property names appearing in the object. XSLT 4.0, by integrating record types into pattern matching syntax, allows such an object to be matched with a pattern of the form match="record(longitude, latitude)"

Rules defining whether one record type is a subtype of another are given in 3.3.2.10 Record Types.

3.2.8.4 Recursive Record Types

A named record type N is said to be recursive if its definition includes a direct or indirect reference to N.

For example, the following XQuery declaration defines a linked list:

declare record my:list (value as item()*, next? as my:list);

The equivalent in XSLT is:

<xsl:item-type name="my:list" 
               as="record(value as item()*, next? as my:list)"/>

Instances of recursive record types can be constructed and interrogated in the normal way. For example a list of length 3 can be constructed as:

{ "value": 1, "next": { "value": 2, "next": { "value": 3 } } }

and the third value in the map can be retrieved as $list?next?next?value. In practice, recursive data structures are usually manipulated using recursive functions.

It is possible to define a recursive record type that cannot be instantiated, because it has no finite instances: for example (in XQuery) declare record X (next as X);. Such a record declaration is implausible, so the processor may treat it as an error [err:XPST0023], but it is not obliged to do so.

Note:

For an example of a practical use of recursive record types, see the specification of the function fn:random-number-generator.

Recursive type definitions need to be handled specially by the subtyping rules; a naïve approach of simply replacing each reference to a named item type with its definition would make the assessment of the subtype relationship non-terminating. For details see 3.3.2 Subtypes of Item Types.

Example: A Binary Tree

A record used to represent a node in a binary tree might be represented (using XQuery syntax) as:

declare record t:binary-tree 
   ( left? as t:binary-tree, 
     value as item()*, 
     right? as t:binary-tree
   )

A recursive function to walk this tree and enumerate all the values in depth-first order might be written (again using XQuery syntax) as:

declare function t:values($tree as t:binary-tree?) as item()* {
  $tree ! (t:values(?left), ?value, t:values(?right))   
}

 

Example: An Arbitrary Tree

A record used to represent a node in a tree where each node has an arbitrary number of children might be represented (using XQuery syntax) as:

declare record t:tree as (value, children as t:tree*);

A function to walk this tree and enumerate all the values in order might be written as:

declare function t:flatten($tree as t:tree) as item()* {
  $tree?value, $tree?children ! t:flatten(.))   
}

 

Example: Mutually Recursive Types

The usual textbook example of mutually-recursive types is that of a forest consisting of a list of trees, where each tree is a record comprising a value and a forest. As the previous example shows, this structure can be defined straightforwardly in XQuery 4.0 without recourse to mutual recursion.

A more realistic example where mutual recursion is needed is for the schema component model used in [XML Schema 1.0] or [XML Schema 1.1]. Simplifying greatly, the data representing an element declaration in XSD may contain references to a complex type, which in turn will typically contain references to further element declarations. The structure therefore involves mutual recursion. A simplified version of the schema component model might be written (in part) as:

declare record ElementDeclaration (
   name as xs:NCName,
   targetNamespace? as xs:anyURI,
   typeDefinition as (SimpleTypeDefinition | ComplexTypeDefinition),
   nillable as xs:boolean,
   abstract as xs:boolean
);
declare record SimpleTypeDefinition (
   name? as xs:NCName,
   targetNamespace? as xs:anyURI,
   baseType? as SimpleTypeDefinition,
   variety as enum("atomic", "list", "union"),
   facets as Facet*,
);
declare record ComplexTypeDefinition (
   name? as xs:NCName,
   targetNamespace? as xs:anyURI,
   baseType? as ComplexTypeDefinition,
   derivationMethod as enum("extension", "restriction"),
   contentType as record (
      variety as enum("empty", "simple", "element-only", "mixed"),
      particle? as Particle,
      simpleTypeDefinition? as SimpleTypeDefinition
   )
);
declare record Particle (
   minOccurs as xs:nonNegativeInteger,
   maxOccurs as (xs:positiveInteger | enum("unbounded")),
   term as (ElementDeclaration | Wildcard | Group)
);
3.2.8.5 Array Type
ArrayType::=AnyArrayType | TypedArrayType
AnyArrayType::="array" "(" "*" ")"
TypedArrayType::="array" "(" SequenceType ")"

The AnyArrayTypearray(*) matches any array. The TypedArrayTypearray(X) matches any array in which every array member matches the SequenceTypeX.

Examples:

  • [ 1, 2 ] instance array(*) returns true()

  • [] instance of array(xs:string) returns true()

  • [ "foo" ] instance of array(xs:string) returns true()

  • [ "foo" ] instance of array(xs:integer) returns false()

  • [ (1, 2), (3, 4) ] instance of array(xs:integer) returns false()

  • [ (1, 2), (3, 4) ] instance of array(xs:integer+) returns true()

An array also matches certain other item types, including:

  • item()

  • function(*)

  • function(xs:integer) as item()*

An array that matches array(T) also matches the function type function(xs:integer) as T.

Note:

To understand this rule, consider the use of an array $A in a function call $A($I), which is equivalent to the function call array:get($A, $I). This function accepts any integer for the argument $I, and the result will either be an instance of T, or an error.

The transitivity rules for item type matching mean that if an item A matches a type T, and T is a subtype of U, then A also matches type U. So the fact that an array of strings (array(xs:string)) matches function(xs:integer) as xs:string means that it will also match other function types such as function(xs:long) as item()*.

Furthermore, the rules for function coercion mean that any array can be supplied as a value in a context where it does not actually match the required function type, but can be coerced to a function that does. For example an array of type array(node()) can be coerced to a function of type function(xs:integer) as element(); in this situation a type error will occur only if a call on the function actually returns a node that is not an element node.

Rules defining whether one array type is a subtype of another are given in 3.3.2.9 Arrays.

3.2.9 xs:error

The type xs:error has an empty value space; it never appears as a dynamic type or as the content type of a dynamic element or attribute type. It was defined in XML Schema in the interests of making the type system complete and closed, and it is also available in XQuery 4.0 for similar reasons.

Note:

Even though it cannot occur in an instance, xs:error is a valid type name in a sequence type. The practical uses of xs:error as a sequence type are limited, but they do exist. For instance, an error-handling function that always raises a dynamic error never returns a value, so xs:error is a good choice for the return type of the function.

The semantics of xs:error are well defined as a consequence of the fact that xs:error is defined as a union type with no member types. For example:

  • $x instance of xs:error always returns false, regardless of the value of $x.

  • $x cast as xs:error fails dynamically with error [err:FORG0001]FO40, regardless of the value of $x.

  • $x cast as xs:error? raises a dynamic error [err:FORG0001]FO40 if exists($x) returns true, and evaluates to the empty sequence if empty($x) returns true.

  • xs:error($x) has the same semantics as $x cast as xs:error? (see the previous bullet point)

  • $x castable as xs:error evaluates to false, regardless of the value of $x.

  • $x treat as xs:error raises a dynamic error [err:XPDY0050] if evaluated, regardless of the value of $x. It never fails statically.

  • let $x as xs:error := 1 return 2 raises a type error [err:XPTY0004], which can be raised statically or dynamically, and need not be raised if the variable $x is never evaluated by the query processor.

  • declare function ns:f($arg as xs:error) {...}; is a valid function declaration, but it always raises a type error [err:XPTY0004] if the function is called.

All of the above examples assume that $x is actually evaluated. The rules specified in 2.4.4 Errors and Optimization permit an implementation to avoid evaluating $x if the result of the query does not depend upon the value of $x and thus to avoid raising an error.

3.3 Subtype Relationships

Changes in 4.0  

  1. The presentation of the rules for the subtype relationship between sequence types and item types has been substantially rewritten to improve clarity; no change to the semantics is intended.  [Issue 196 PR 202 25 October 2022]

[Definition: Given two sequence types or item types, the rules in this section determine if one is a subtype of the other. If a type A is a subtype of type B, it follows that every value matched by A is also matched by B.]

Note:

The relationship subtype(A, A) is always true: every type is a subtype of itself.

Note:

The converse is not necessarily true: we cannot infer that if every value matched by A is also matched by B, then A is a subtype of type B. For example, A might be defined as the set of strings matching the regular expression [A-Z]*, while B is the set of strings matching the regular expression [A-Za-z]*; no subtype relationship holds between these types.

The rules for deciding whether one sequence type is a subtype of another are given in 3.3.1 Subtypes of Sequence Types. The rules for deciding whether one item type is a subtype of another are given in 3.3.2 Subtypes of Item Types.

Note:

The subtype relationship is not acyclic. There are cases where subtype(A, B) and subtype(B, A) are both true. This implies that A and B have the same value space, but they can still be different types. For example this applies when A is a union type with member types xs:string and xs:integer, while B is a union type with member types xs:integer and xs:string. These are different types ("23" cast as A produces a string, while "23" cast as B produces an integer, because casting is attempted to each member type in order) but both types have the same value space.

3.3.1 Subtypes of Sequence Types

We use the notation A ⊑ B, or subtype(A, B) to indicate that a sequence typeA is a subtype of a sequence type B. This section defines the rules for deciding whether any two sequence types have this relationship.

To define the rules, we divide sequence types into six categories:

  • The category empty includes the sequence types empty-sequence(), xs:error* and xs:error?. All these sequence types match the empty sequence as their only instance.

  • The category void includes the sequence types xs:error and xs:error+, which have no instances (not even the empty sequence).

  • The categories X?, X*, X and X+ includes all sequence types having an item type X other than xs:error, together with an occurrence indicator of ? (zero or more), * (one or more), absent (exactly one), or + (one or more) respectively. We use the notation Xi to indicate the item type of such a sequence type.

The judgement A ⊑ B is then determined by the categories of the two sequence types, as defined in the table below. In many cases this depends on the relationship between the item types of A and B. This is denoted using the notation AiBi, as defined in 3.3.2 Subtypes of Item Types.

Sequence typeB
emptyBi?Bi*BiBi+void
Sequence typeAemptytruetruetruefalsefalsefalse
Ai?falseAiBiAiBifalsefalsefalse
Ai*falsefalseAiBifalsefalsefalse
AifalseAiBiAiBiAiBiAiBifalse
Ai+falsefalseAiBifalseAiBifalse
voidtruetruetruetruetruetrue

3.3.2 Subtypes of Item Types

We use the notation A ⊆ B, or itemtype-subtype(A, B) to indicate that an item typeA is a subtype of an item type B. This section defines the rules for deciding whether any two item types have this relationship.

The rules in this section apply to item types, not to item type designators. For example, if the name STR has been defined in the static context as a named item type referring to the type xs:string, then anything said here about the type xs:string applies equally whether it is designated as xs:string or as STR, or indeed as the parenthesized forms (xs:string) or (STR).

References to named item types are handled as described in 3.3.2.11 Named Item Types.

The relationship A ⊆ B is true if and only if at least one of the conditions listed in the following subsections applies:

3.3.2.1 General Rules

Given item typesA and B, AB is true if any of the following apply:

  1. A is xs:error.

  2. B is item().

  3. A and B are the same item type.

  4. There is an item typeX such that AX and XB. (This is referred to below as the transitivity rule).

Note:

The first rule is technically redundant: it is implied by the second rule in 3.3.2.3 Atomic and Union Types. The type xs:error is defined as a union type with no member types; therefore it is automatically true that every member type T satisfies TB.

3.3.2.2 Choice Item Types

The following rules determine whether AB is true in the case where either A or B or both is a choice item type.

Firstly, if one of the operands is not a choice item type, then it is treated as a choice item type with a single member type. The rule is then:

AB is true if for every member type a in A, there is a member type b in B such that ab.

For example, (xs:int | xs:long) is a subtype of (xs:decimal | xs:date) because both xs:int and xs:long are subtypes of xs:decimal.

Note:

Because an enumeration type is defined as a choice type of singleton enumerations, these rules have the consequence, for example, that enum("A", "B") is a subtype of enum("A", "B", "C").

Note:

The type xs:int is not a subtype of (xs:negativeInteger | xs:nonNegativeInteger), because it does not satisfy this rule. This is despite the fact that the value space of xs:int is a subset of the value space of (xs:negativeInteger | xs:nonNegativeInteger).

3.3.2.3 Atomic and Union Types

Given item types A and B, AB is true if any of the following apply:

  1. A and B are generalized atomic types, and derives-from(A, B) returns true.

    The derives-from relationship is defined in 3.1.2 Sequence Type Matching.

    Examples:
    • xs:integer ⊆ xs:decimal because xs:integer is derived by restriction from xs:decimal.

    • xs:decimal ⊆ xs:numeric because xs:numeric is a pure union type that includes xs:decimal as a member type.

    • enum("red") ⊆ xs:string because the singleton enumeration type enum("red") is defined to be an atomic type derived from xs:string.

    • enum("red") ⊆ enum("red", "green") because the enumeration type enum("red", "green") is defined to be a union type that has the generalized atomic type enum("red") as a member type.

  2. A is a pure union type, and every type T in the transitive membership of A satisfies TB.

    Examples:
    • (xs:short | xs:long) ⊆ xs:integer because xs:short ⊆ xs:integer and xs:long ⊆ xs:integer.

    • (P | Q) ⊆ (P | Q | R) because P ⊆ (P | Q | R) and Q ⊆ (P | Q | R).

    • enum("red", "green") ⊆ xs:string because the enumeration type enum("red") ⊆ xs:string and enum("green") ⊆ xs:string.

    • enum("red", "green") ⊆ enum("red", "green", "blue") because enum("red") ⊆ enum("red", "green", "blue") and enum("green") ⊆ enum("red", "green", "blue").

    • enum("red", "green", "blue") ⊆ (enum("red", "green") | enum("blue")) because each of the types enum("red"), enum("green"), and enum("blue") is a subtype of one of the two members of the union type.

3.3.2.4 Node Types: General Rules

Given item types A and B, AB is true if any of the following apply:

  1. A is a KindTest and B is node().

    Example:

    comment() ⊆ node()

  2. A is processing-instruction(N) for any name N, and B is processing-instruction().

    Example:

    processing-instruction('pi') ⊆ processing-instruction()

  3. A is document-node(E) for any E, and B is document-node().

    Examples:

    document-node(element(chap)) ⊆ document-node()

    document-node(*) ⊆ document-node()

  4. All the following are true, after expanding document-node(NameTestUnion) to document-node(element(NameTestUnion)):

    1. A is document-node(Ae)

    2. B is document-node(Be)

    3. AeBe

    Examples:

    document-node(element(title)) ⊆ document-node(element(*)).

    document-node(title) ⊆ document-node(*).

3.3.2.5 Node Types: Element Tests

[Definition: In these rules, if MU and NU are NameTestUnions, then MUwildcard-matchesNU is true if every name that matches MU also matches NU.]

More specifically, this is the case if for every NameTestM in MU there is a NameTestN in NU where at least one of the following applies:

  1. M and N are the same NameTest.

  2. M is an EQName and N is a Wildcard that matches M.

  3. N is the Wildcard*.

Given item types A and B, AB is true if any of the following apply.

  1. A is an ElementTest and B is either element() or element(*)

  2. All the following are true:

    1. A is either element(An) or element(An, T) or element(An, T?) for any type T

    2. B is either element(Bn) or element(Bn, xs:anyType?)

    3. Anwildcard-matchesBn

    Examples:
    • element(title) ⊆ element(*)

    • element(title, xs:string) ⊆ element(*)

    • element(title|heading, xs:string) ⊆ element(*)

    • element(title, xs:string) ⊆ element(title|heading)

    • element(title, xs:string?) ⊆ element(*)

    • element(title|heading, xs:string) ⊆ element(*)

    • element(title) ⊆ element(title, xs:anyType?)

    • element(title, xs:integer) ⊆ element(title|heading, xs:anyType?)

    • element(title, xs:string?) ⊆ element(title, xs:anyType?)

    • element(my:title|your:title) ⊆ element(*:title)

    • element(my:title|my:heading) ⊆ element(my:*)

  3. All the following are true:

    1. A is element(An, At)

    2. B is element(Bn, Bt)

    3. Anwildcard-matchesBn

    4. derives-from(At, Bt).

    Examples:
    • element(size, xs:integer) ⊆ element(size, xs:decimal)

    • element(size, xs:integer) ⊆ element(size|größe, xs:decimal)

    • element(size, xs:integer) ⊆ element(*, xs:decimal)

    • element(*, xs:integer) ⊆ element(*, xs:decimal)

    • element(my:*, xs:integer) ⊆ element(*, xs:decimal)

  4. All the following are true:

    1. A is either element(An, At) or element(An, At?)

    2. B is element(Bn, Bt?)

    3. Anwildcard-matchesBn

    4. derives-from(At, Bt).

    Examples:
    • element(size, xs:integer) ⊆ element(size, xs:decimal?)

    • element(size, xs:integer?) ⊆ element(*, xs:decimal?)

    • element(*, xs:integer) ⊆ element(*, xs:decimal?)

    • element(my:*, xs:integer?) ⊆ element(*, xs:decimal?)

  5. All the following are true:

    1. A is schema-element(An)

    2. B is schema-element(Bn)

    3. Every element declaration that is an actual member of the substitution group of An is also an actual member of the substitution group of Bn.

    Note:

    The fact that P is a member of the substitution group of Q does not mean that every element declaration in the substitution group of P is also in the substitution group of Q. For example, Q might block substitution of elements whose type is derived by extension, while P does not.

  6. A is element(A1|A2|..., T) (where T may be absent), and for each An, element(An, T) ⊆ B.

    Examples:
    • element(a|b) ⊆ (element(a)|element(b)|element(c))

    • element(a|b, xs:integer) ⊆ (element(a, xs:decimal) | element(b, xs:integer))

3.3.2.6 Node Types: Attribute Tests

Given item types A and B, AB is true if any of the following apply:

  1. A is an AttributeTest and B is either attribute() or attribute(*)

  2. All the following are true:

    1. A is either attribute(An) or attribute(An, T) for any type T.

    2. B is either attribute(Bn) or attribute(Bn, xs:anyAtomicType)

    3. Anwildcard-matchesBn

    Examples:
    • attribute(code) ⊆ attribute(*)

    • attribute(code|status) ⊆ attribute(*)

    • attribute(code, xs:untypedAtomic) ⊆ attribute(*)

    • attribute(code|status, xs:string) ⊆ attribute(code, xs:anyAtomicType)

    • attribute(my:code|your:code) ⊆ attribute(*:code)

    • attribute(my:code|my:status) ⊆ attribute(my:*)

  3. All the following are true:

    1. A is attribute(An, At)

    2. B is attribute(Bn, Bt)

    3. Anwildcard-matchesBn

    4. derives-from(At, Bt).

    Examples:
    • attribute(*, xs:ID) ⊆ attribute(*, xs:string)

    • attribute(my:*, xs:ID) ⊆ attribute(*, xs:string)

    • attribute(code, xs:ID) ⊆ attribute(code|status, xs:string)

    • attribute(code, xs:ID) ⊆ attribute(*, xs:string)

    • attribute(code, xs:ID) ⊆ attribute(*:code, xs:ID)

    • attribute(my:code|my:status, xs:ID) ⊆ attribute(my:*, xs:string)

  4. All the following are true:

    1. A is schema-attribute(An)

    2. B is schema-attribute(Bn)

    3. the expanded QName of An equals the expanded QName of Bn

  5. A is attribute(A1|A2|..., T) (where T may be absent), and for each An, attribute(An, T) ⊆ B.

    Examples:
    • attribute(a|b) ⊆ (attribute(a)|attribute(b)|attribute(c))

    • attribute(a|b, xs:integer) ⊆ (attribute(a, xs:decimal) | attribute(b))

3.3.2.7 Functions

Given item types A and B, AB is true if any of the following apply:

  1. All the following are true:

    1. A is a FunctionType with annotations [AnnotationsA]

    2. B is [AnnotationsB] function(*)

    3. subtype-assertions(AnnotationsA, AnnotationsB), where [AnnotationsB] and [AnnotationsA] are optional lists of one or more annotations.

    Example:

    function(xs:integer) as xs:string ⊆ function(*)

  2. All the following are true:

    1. A is AnnotationsA function(a1, a2, ... aM) as RA

    2. B is AnnotationsB function(b1, b2, ... bN) as RB

    3. [AnnotationsB] and [AnnotationsA] are optional lists of one or more annotations;

    4. N (the arity of B) equals M (the arity of A)

    5. RARB

    6. For all values of p between 1 and N, bpap, and subtype-assertions(AnnotationsA, AnnotationsB)

    Examples:
    • function(xs:integer) as xs:string ⊆ function(xs:long) as xs:string

    • function(xs:integer) as xs:ID ⊆ function(xs:integer) as xs:string

    • function(xs:integer) as xs:ID ⊆ function(xs:long) as xs:string

    Note:

    Function return types are covariant because this rule requires RARB for return types. Function parameter types are contravariant because this rule requires bpap for parameter types.

3.3.2.8 Maps

Given item types A and B, AB is true if any of the following apply:

  1. Both of the following are true:

    1. A is map(K, V), for any K and V

    2. B is map(*)

    Example:

    map(xs:integer, item()*) ⊆ map(*)

  2. All the following are true:

    1. A is map(Ka, Va)

    2. B is map(Kb, Vb)

    3. KaKb

    4. VaVb

    Example:

    map(xs:long, item()) ⊆ map(xs:integer, item()+)

  3. Both the following are true:

    1. A is map(*) (or, because of the transitivity rules, any other map type)

    2. B is function(*)

    Example:

    map(xs:long, xs:string?) ⊆ function(*)

  4. Both the following are true:

    1. A is map(*) (or, because of the transitivity rules, any other map type)

    2. B is function(xs:anyAtomicType) as item()*

    Example:

    map(xs:long, xs:string?) ⊆ function(xs:anyAtomicType) as item()*

  5. All the following are true:

    1. A is map(K, V)

    2. B is function(xs:anyAtomicType) as R

    3. VR

    4. empty-sequence()R

    Examples:
    • map(xs:int, node()) ⊆ function(xs:anyAtomicType) as node()?

    • map(xs:int, node()+) ⊆ function(xs:anyAtomicType) as node()*

    The function accepts type xs:anyAtomicType rather than xs:int, because $M("xyz") is a valid call on a map (treated as a function) even when all the keys in the map are integers.

    The return type of the function is extended from node() or node()+ to allow an empty sequence because $M("xyz") can return an empty sequence even if none of the entries in the map contains an empty sequence.

3.3.2.9 Arrays

Given item types A and B, AB is true if any of the following apply:

  1. Both the following are true:

    1. A is array(X)

    2. B is array(*)

    Example:

    array(xs:integer) ⊆ array(*)

  2. All the following are true:

    1. A is array(X)

    2. B is array(Y)

    3. XY

    Example:

    array(xs:integer) ⊆ array(xs:decimal+)

  3. Both the following are true:

    1. A is array(*) (or, because of the transitivity rules, any other array type)

    2. B is function(*)

    Example:

    array(xs:integer) ⊆ function(*)

  4. Both the following are true:

    1. A is array(*) (or, because of the transitivity rules, any other array type)

    2. B is function(xs:integer) as item()*

    Example:

    array(*) ⊆ function(xs:integer) as item()*

  5. Both the following are true:

    1. A is array(X)

    2. B is function(xs:integer) as X

    Example:

    array(xs:string) ⊆ function(xs:integer) as xs:string

3.3.2.10 Record Types

Given item types A and B, AB is true if any of the following apply:

  1. A is map(*) and B is record(*).

  2. All of the following are true:

    1. A is a record type.

    2. B is map(*) or record(*).

    Examples:

    record(longitude, latitude)map(*)

    record(longitude, latitude, *)record(*)

    record(*)map(*)

  3. All of the following are true:

    1. A is a non-extensible record type

    2. B is map(K, V)

    3. K is either xs:string or xs:anyAtomicType

    4. For every field F in A, where T is the declared type of F (or its default, item()*), TV.

    Examples:
    • record(x, y)map(xs:string, item()*)

    • record(x as xs:double, y as xs:double)map(xs:string, xs:double)

  4. All of the following are true:

    1. A is a non-extensible record type.

    2. B is a non-extensible record type.

    3. Every field in A is also declared in B.

    4. Every mandatory field in B is also declared as mandatory in A.

    5. For every field that is declared in both A and B, where the declared type in A is T and the declared type in B is U, TU.

    Examples:
    • record(x, y as xs:integer) ⊆ record(x, y as xs:decimal)

    • record(x, y) ⊆ record(x, y, z?)

  5. All of the following are true:

    1. A is an extensible record type

    2. B is an extensible record type

    3. Every mandatory field in B is also declared as mandatory in A.

    4. For every field that is declared in both A and B, where the declared type in A is T and the declared type in B is U, TU.

    5. For every field that is declared in B but not in A, the declared type in B is item()*.

    Examples:
    • record(x, y, z, *) ⊆ record(x, y, *)

    • record(x?, y?, z?, *) ⊆ record(x, y, *)

    • record(x as xs:integer, y as xs:integer, *) ⊆ record(x as xs:decimal, y as xs:integer*, *)

    • record(x as xs:integer, *) ⊆ record(x as xs:decimal, y as item(), *)

  6. All of the following are true:

    1. A is a non-extensible record type.

    2. B is an extensible record type.

    3. Every mandatory field in B is also declared as mandatory in A.

    4. For every field that is declared in both A and B, where the declared type in A is T and the declared type in B is U, TU.

    Examples:
    • record(x, y as xs:integer) ⊆ record(x, y as xs:decimal, *)

    • record(y as xs:integer) ⊆ record(x?, y as xs:decimal, *)

3.3.2.11 Named Item Types

This section describes how references to named item types are handled when evaluating the subtype relationship.

Named item types can be classified as recursive or non-recursive. A recursive type is one that references itself, directly or indirectly. Only named record types are allowed to be recursive.

In the case of references to non-recursive named item types, the reference is fully expanded as the first step in evaluating the subtype relationship. For example this means that if U is a named item type with the expansion (xs:integer | xs:double), then xs:integer ⊆ U is true, because xs:integer ⊆ (xs:integer | xs:double) is true.

Recursive record types are considered to be, in the terminology of the computer science literature, iso-recursive (rather than equi-recursive). This means that a recursive type name is not treated as being equivalent to its expansion (at any depth). For example, if the named item type T has the expansion record(A as item()*, B as T?), then the type array(T) is not considered to be equivalent to array(record(A as item()*, B as T?)), despite the fact that the two types have exactly the same instances.

The rules are therefore defined as follows:

  • If B is a reference to a recursive record type, then AB is true if and only if A and B are references to the same named record type.

  • If A is a reference to a recursive named item type, then AB is true if either:

    • A and B are references to the same named record type.

    • record(*) ⊆ B.

      Note:

      This is because only record types are allowed to be recursive.

Note:

The decision to make recursive types iso-recursive rather than equi-recursive was made largely because it saves a great deal of implementation complexity without any serious adverse effects for users. In practice, problems can be avoided by using named record types consistently (for example, avoiding having two named record types with different names but identical definitions).

3.3.3 The judgement subtype-assertions(AnnotationsA, AnnotationsB)

The judgement subtype-assertions(AnnotationsA, AnnotationsB) determines if AnnotationsA is a subtype of AnnotationsB, where AnnotationsA and AnnotationsB are annotation lists from two FunctionTypes. It is defined to ignore function assertions in namespaces not understood by the XQuery implementation. For assertions that are understood, their effect on the result of subtype-assertions() is implementation defined.

The following examples are some possible ways to define subtype-assertions() for some implementation defined assertions in the local namespace. These examples assume that some implementation uses annotations to label functions as deterministic or nondeterministic, and treats deterministic functions as a subset of nondeterministic functions. In this implementation, nondeterministic functions are not a subset of deterministic functions.

  • AnnotationsA is

    %local:inline

    It has no influence on the outcome of subtype-assertions().

  • AnnotationsA is

    %local:deterministic

    AnnotationsB is

    %local:nondeterministic

    Since deterministic functions are a subset of nondeterministic functions, subtype-assertions() is true.

  • AnnotationsA contains

    %local:nondeterministic

    AnnotationsB is empty. If FunctionTypes without the %local:nondeterministic annotation only match deterministic functions, subtype-assertions() must be false.

3.4 Coercion Rules

Changes in 4.0  

  1. The term "function conversion rules" used in 3.1 has been replaced by the term "coercion rules".   [ PR 254 29 November 2022]

  2. The coercion rules allow “relabeling” of a supplied atomic item where the required type is a derived atomic type: for example, it is now permitted to supply the value 3 when calling a function that expects an instance of xs:positiveInteger.   [Issue 117 PR 254 29 November 2022]

  3. The coercion rules now allow any numeric type to be implicitly converted to any other, for example an xs:double is accepted where the required type is xs:double.   [Issue 980 PR 911 30 January 2024]

  4. The coercion rules now allow conversion in either direction between xs:hexBinary and xs:base64Binary.   [Issues 130 480 PR 815 7 November 2023]

[Definition: The coercion rules are rules used to convert a supplied value to a required type, for example when converting an argument of a function call to the declared type of the function parameter. ] The required type is expressed as a sequence type. The effect of the coercion rules may be to accept the value as supplied, to convert it to a value that matches the required type, or to reject it with a type error.

This section defines how the coercion rules operate; the situations in which the rules apply are defined elsewhere, by reference to this section.

Note:

In previous versions of this specification, the coercion rules were referred to as the function conversion rules. The terminology has changed because the rules are not exclusively associated with functions or function calling.

If the required type is empty-sequence(), no coercion takes place (the supplied value must be an empty sequence, or a type error occurs).

In all other cases, the required sequence typeT comprises a required item typeR and an optional occurrence indicator. The coercion rules are then applied to a supplied value V and the required type T as follows:

  1. Each item in V is processed against the required item type R using the item coercion rules defined in 3.4.1 Item Coercion Rules, and the results are sequence-concatenated into a single sequence V′.

  2. A type error is raised if the cardinality of V′ does not match the required cardinality of T [err:XPTY0004].

3.4.1 Item Coercion Rules

The rules in this section are used to process each item J in a supplied sequence, given a required item typeR.

  1. If R is a generalized atomic type (for example, if it is an atomic type, a pure union type, or an enumeration type), and J is not an atomic item, then:

    1. J is atomized to produce a sequence of atomic items JJ.

    2. Each atomic item in JJ is coerced to the required type R by recursive application of the item coercion rules (the rules in this section) to produce a value V.

    3. The result is the sequence-concatenation of the V values.

    Note:

    For example, if J is an element with type annotation xs:integer, and R is the union type xs:numeric, then the effect is to atomize the element to an xs:integer, and then to coerce the resulting xs:integer to xs:numeric (which leaves the integer unchanged). This is not the same as attempting to coerce the element to each of the alternatives of the union type in turn, which would deliver an instance of xs:double.

  2. Otherwise, if R is a choice item type or a pure union type (which includes the case where it is an enumeration type), then:

    1. If J matches (is an instance of) one of the alternatives in R, then:

      1. If the first alternative in R that J matches is a typed function type (see 3.2.8.1 Function Type), then function coercion is applied to coerce J to that function type, as described in 3.4.3 Function Coercion.

      2. Otherwise, J is used as is.

    2. Otherwise, the item coercion rules (the rules in this section) are applied to J recursively with R set to each of the alternatives in the choice or union item type, in order, until an alternative is found that does not result in a type error; a type error is raised only if all alternatives fail.

      The error code used in the event of failure should be the error code arising from the first unsuccessful matching attempt. (The diagnostic information associated with the error may also describe how further attempts failed.)

    Note:

    Suppose the required type is (xs:integer | element(e))* and the supplied value is the sequence (<e>22</e>, 23, <f>24</f>). Item coercion is applied independently to each of the three items in this sequence. The first item matches one of the alternatives, namely element(e), so it is returned unchanged as an element node. The second item (the integer 23) also matches one of the alternatives, and is returned unchanged as an integer. The third item does not match any of the alternatives, so coercion is attempted to each one in turn. Coercion to type xs:integer succeeds (by virtue of atomization and untyped atomic conversion), so the final result is the sequence (<e>22</e>, 23, 24)

    Note:

    Suppose the required type is enum("red", "green", "blue") and the supplied value is "green". The enumeration type is defined as a choice item type whose alternatives are singleton enumerations, so the rules are applied first to the type enum("red") (which fails), and then to the type enum("green") (which succeeds). The strings in an enumeration type are required to be distinct so the order of checking is in this case immaterial. The supplied value will be accepted, and will be relabeled as an instance of enum("green"), which is treated as a schema type equivalent to a type derived from xs:string by restriction.

    Note:

    Schema-defined union types behave in exactly the same way as choice item types.

  3. If R is an atomic type and J is an atomic item, then:

    1. If J is an instance of R then it is used unchanged.

    2. If J is an instance of type xs:untypedAtomic then:

      1. If R is an enumeration type then A is cast to xs:string.

      2. If R is namespace-sensitive then a type error [err:XPTY0117] is raised.

    3. Otherwise, J is cast to type R.

  4. If there is an entry (from, to) in the following table such that J is an instance of from, and to is R, then J is cast to type R.

    Implicit Casting
    fromto
    xs:decimalxs:double
    xs:doublexs:decimal
    xs:decimalxs:float
    xs:floatxs:decimal
    xs:floatxs:double
    xs:doublexs:float
    xs:stringxs:anyURI
    xs:anyURIxs:string
    xs:hexBinaryxs:base64Binary
    xs:base64Binaryxs:hexBinary

    Note:

    The item type in the to column must match R exactly; however, J may belong to a subtype of the type in the from column.

    For example, an xs:NCName will be cast to type xs:anyURI, but an xs:anyURI will not be cast to type xs:NCName.

    Similarly, an xs:integer will be cast to type xs:double, but an xs:double will not be cast to type xs:integer.

  5. If R is derived from some primitive atomic type P, then J is relabeled as an instance of R if it satisfies all the following conditions:

    • J is an instance of P.

    • J is not an instance of R.

    • The datumDM of J is within the value space of R.

    Relabeling an atomic item changes the type annotation but not the datumDM. For example, the xs:integer value 3 can be relabeled as an instance of xs:unsignedByte, because the datum is within the value space of xs:unsignedByte.

    Note:

    Relabeling is not the same as casting. For example, the xs:decimal value 10.1 can be cast to xs:integer, but it cannot be relabeled as xs:integer, because its datum not within the value space of xs:integer.

    Note:

    The effect of this rule is that if, for example, a function parameter is declared with an expected type of xs:positiveInteger, then a call that supplies the literal value 3 will succeed, whereas a call that supplies -3 will fail.

    This differs from previous versions of this specification, where both these calls would fail.

    This change allows the arguments of existing functions to be defined with a more precise type. For example, the $position argument of array:get could be defined as xs:positiveInteger rather than xs:integer.

    Note:

    If T is a union type with members xs:negativeInteger and xs:positiveInteger)* and the supplied value is the sequence (20, -20), then the effect of these rules is that the first item 20 is relabeled as type xs:positiveInteger and the second item -20is relabeled as type xs:negativeInteger.

    Note:

    Promotion (for example of xs:float to xs:double) occurs only when T is a primitive type. Relabeling occurs only when T is a derived type. Promotion and relabeling are therefore never combined.

    Note:

    A singleton enumeration type such as enum("green") is treated as an atomic type derived by restriction from xs:string; so if the xs:string value "green" is supplied in a context where the required type is enum("red", "green", "blue"), the value will be accepted and will be relabeled as an instance of enum("green").

  6. If R is an ArrayType other than array(*) and J is an array, then J is converted to a new array by converting each member to the required member type by applying the coercion rules recursively.

    Note:

    For example, if the required type is array(xs:double) and the supplied value is [ 1, 2 ], the array is converted to [ 1e0, 2e0 ].

  7. If R is a MapType other than map(*) and J is a map, then J is converted to a new map as follows:

    1. Each key in the supplied map is converted to the required map key type by applying the coercion rules. If the resulting map would contain duplicate keys, a type error is raised [err:XPTY0004].

    2. The corresponding value is converted to the required map value type by applying the coercion rules recursively.

    Note:

    For example, if the required type is map(xs:string, xs:double) and the supplied value is { "x": 1, "y": 2 }, the map is converted to { "x": 1e0, "y": 2e0 }.

    Note:

    Duplicate keys can occur if the value space of the target type is more restrictive than the original type. For example, an error is raised if the map { 1.2: 0, 1.2000001: 0 }, which contains two keys of type xs:decimal, is coerced to the type map(xs:float, xs:integer).

  8. If R is a RecordType and J is a map, then J is converted to a new map as follows:

    1. The keys in the supplied map are unchanged.

    2. In any map entry whose key is an xs:string equal to the name of one of the field declarations in R, the corresponding value is converted to the required type defined by that field declaration, by applying the coercion rules recursively (but with XPath 1.0 compatibility mode treated as false).

    Note:

    For example, if the required type is record(longitude as xs:double, latitude as xs:double) and the supplied value is { "longitude": 0, "latitude": 53.2 }, then the map is converted to { "longitude": 0.0e0, "latitude": 53.2e0 }.

  9. If R is a TypedFunctionType and J is a function item, then function coercion is applied to J.

    Note:

    Function coercion applies even if J is already an instance of R.

    Maps and arrays are functions, so function coercion applies to them as well.

  10. If, after the above conversions, the resulting item does not match the expected item type R according to the rules for SequenceType Matching, a type error is raised [err:XPTY0004].

    Note:

    Under the general rules for type errors (see 2.4.1 Kinds of Errors), a processor may report a type error during static analysis if it will necessarily occur when the expression is evaluated. For example, the function call fn:abs("beer") will necessarily fail when evaluated, because the function requires a numeric value as its argument; this may be detected and reported as a static error.

3.4.2 Implausible Coercions

An expression is deemed to be implausible [err:XPTY0006] if the static type of the expression, after applying all necessary coercions, is substantively disjoint with the required type T.

[Definition: Two sequence types are deemed to be substantively disjoint if (a) neither is a subtype of the other (see 3.3.1 Subtypes of Sequence Types) and (b) the only values that are instances of both types are one or more of the following:

  • The empty sequence, ().

  • The empty map, {}.

  • The empty array, [].

]

Note:

Examples of pairs of sequence types that are substantively disjoint include:

  • xs:integer* and xs:string*

  • map(xs:integer, node()) and map(xs:string, node())

  • array(xs:integer) and array(xs:string)

For example, supplying a value whose static type is xs:integer* when the required type is xs:string* is implausible, because it can succeed only in the special case where the actual value supplied is an empty sequence.

Note:

The case where the supplied type and the required type are completely disjoint (for example map(*) and array(*)) is covered by the general rules for type errors: that case can always be reported as a static error.

Examples of implausible coercions include the following:

  • round(timezone-from-time($now)). The result of fn:timezone-from-time is of type xs:dayTimeDuration?, which is substantively disjoint with the required type of fn:round, namely xs:numeric?.

  • function($x as xs:integer) as array(xs:string) { array { 1 to $x } }. The type of the function body is array(xs:integer), which is substantively disjoint with the required type array(xs:string): the function can succeed only in the exceptional case where the function body delivers an empty array.

3.4.3 Function Coercion

Changes in 4.0  

  1. Function coercion now allows a function with arity N to be supplied where a function of arity greater than N is expected. For example this allows the function true#0 to be supplied where a predicate function is required.

  2. It has been clarified that function coercion applies even when the supplied function item matches the required function type. This is to ensure that arguments supplied when calling the function are checked against the signature of the required function type, which might be stricter than the signature of the supplied function item.   [Issue 1020 PRs 1023 1128 9 April 2024]

Function coercion is a transformation applied to function items during application of the coercion rules. [Definition: Function coercion wraps a function item in a new function whose signature is the same as the expected type. This effectively delays the checking of the argument and return types until the function is called.]

Given a function F, and an expected function type T, function coercion proceeds as follows:

  1. If F has higher arity than T, a type error is raised [err:XPTY0004]

  2. If F has lower arity than T, then F is wrapped in a new function that declares and ignores the additional argument; the following steps are then applied to this new function.

    For example, if T is function(node(), xs:boolean) as xs:string, and the supplied function is fn:name#1, then the supplied function is effectively replaced by function($n as node(), $b as xs:boolean) as xs:string { fn:name($n) }

    Note:

    This mechanism makes it easier to design versatile and extensible higher-order functions. For example, in previous versions of this specification, the second argument of the fn:filter function expected an argument of type function(item()) as xs:boolean. This has now been extended to function(item(), xs:integer) as xs:boolean, but existing code continues to work, because callback functions that are not interested in the value of the second argument simply ignore it.

  3. A type error is raised [err:XPTY0004] if, for any parameter type, or for the result type, the relevant type in the signature of the supplied function and the relevant type in the expected function type are substantively disjoint.

    For example, the types xs:integer and xs:string are substantively disjoint, so a function with signature function(xs:integer) as xs:boolean cannot be supplied where the expected type is function(xs:string) as xs:boolean.

  4. Function coercion then returns a new function item with the following properties (as defined in Section 2.9.4 Function ItemsDM):

    • name: The name of F(if not absent).

    • identity: A new function identity distinct from the identity of any other function item.

    • parameter names: The parameter names of F.

    • signature: Annotations is set to the annotations of F. TypedFunctionType is set to the expected type.

    • implementation: In effect, a FunctionBody that calls F, passing it the parameters of this new function, in order.

    • nonlocal variable bindings: An empty mapping.

These rules have the following consequences:

  • SequenceType matching of the function’s arguments and result are delayed until that function is called.

  • When the coerced function is called, the supplied arguments must match the parameter typed defined in T; it is not sufficient to match the parameter types defined in F.

  • The coercion rules rules applied to the function’s arguments and result are defined by the SequenceType it has most recently been coerced to. Additional coercion rules could apply when the wrapped function is called.

  • If an implementation has static type information about a function, that can be used to type check the function’s argument and return types during static analysis.

  • When function coercion is applied to a map or an array, the resulting function is not a map or array, and cannot be used as such. For example, the expression

    let $f as function(xs:integer) as xs:boolean := { 0: false(), 1: true() }
    return $f?0

    raises a type error, because a lookup expression requires the left hand operand to be a map or array, and $f is neither.

  • When function types are used as alternatives in a choice item type, the supplied function is coerced to the first alternative for which coercion does not raise a type error. In this situation it is important to write the alternatives in order, with the most specific first.

For instance, consider the following query:

declare function local:filter(
  $s as item()*, 
  $p as function(xs:string) as xs:boolean
) as item()* {
  $s[$p(.)]
};
let $f := function($a) { starts-with($a, "E") }
return local:filter(("Ethel", "Enid", "Gertrude"), $f)

The function $f has a static type of function(item()*) as item()*. When the local:filter() function is called, the following occurs to the function:

  1. The coercion rules result in applying function coercion to $f, wrapping $f in a new function ($p) with the signature function(xs:string) as xs:boolean.

  2. $p is matched against the SequenceType of function(xs:string) as xs:boolean, and succeeds.

  3. When $p is called inside the predicate, coercion and SequenceType matching rules are applied to the context value argument, resulting in an xs:string value or a type error.

  4. $f is called with the xs:string, which returns an xs:boolean.

  5. $p applies coercion rules to the result sequence from $f, which already matches its declared return type of xs:boolean.

  6. The xs:boolean is returned as the result of $p.

Note:

The semantics of function coercion are specified in terms of wrapping the functions. Static typing may be able to reduce the number of places where this is actually necessary. However, it cannot be assumed that because a supplied function is an instance of the required function type, no function coercion is necessary: the supplied function might not perform all required checks on the types of its arguments.

Since maps and arrays are also functions in XQuery 4.0, function coercion applies to them as well. For instance, consider the following expression:

let $m := {
  "Monday" : true(),
  "Wednesday" : false(),
  "Friday" : true()
}
let $days := ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday")
return filter($days, $m)

The map $m is an instance of function(xs:anyAtomicType?) as item()*. When the fn:filter() function is called, the following occurs to the map:

  1. The map $m is treated as a function equivalent to map:get($m, ?).

  2. The coercion rules result in applying function coercion to this function, wrapping it in a new function (M′) with the signature function(item(), xs:integer) as xs:boolean.

  3. When M′ is called by fn:filter(), coercion and SequenceType matching rules are applied to the argument, resulting in an item() value ($a) or a type error.

  4. The function map:get($m, ?) is called with $a as the argument; this returns either an xs:boolean or the empty sequence (call the result R).

  5. The wrapper function $p applies the coercion rules to R. If R is an xs:boolean the matching succeeds. When it is an empty sequence (in particular, $m does not contain a key for "Tuesday"), a type error is raised [err:XPTY0004], since the expected type is xs:boolean and the actual type is an empty sequence.

Consider the following expression:

let $m := {
   "Monday" : true(),
   "Wednesday" : false(),
   "Friday" : true(),
}
let $days := ("Monday", "Wednesday", "Friday")
return filter($days, $m)

In this case the result of the expression is the sequence ("Monday", "Friday"). But if the input sequence included the string "Tuesday", the filter operation would fail with a type error.

Note:

Function coercion applies even if the supplied function matches the required type.

For example, consider this case:

declare function local:filter(
  $s as item()*, 
  $p as function(xs:string) as xs:boolean
) as item()* {
  $s[$p(.)]
};

let $f := function($a) { $a mod 2 = 0 }
return local:filter(1 to 10, $f)

Here the supplied function $f is an instance of the required type, because its signature defaults the argument type to item()*, which is a supertype of xs:string. The expression $s[$p(.)] could in principle succeed. However, function coercion ensures that the supplied function is wrapped in a function that requires the argument to be of type xs:string, so the call fails with a type error when the wrapping function is invoked supplying an xs:integer as the argument.

This has the consequence that in XQuery 4.0, there is a backwards incompatibility introduced because coercion rules now apply to global variable declarations (declare variable) and local variable bindings (for example let clauses). Previously the following would execute without error:

let $f as function(xs:integer) as item()* := function($x) { $x + 1 }
return $f(12.3)

With XQuery 4.0, as a consequence of function coercion, this fails with a type error because the argument supplied in the function call is not of type xs:integer.

3.4.4 Examples of Coercions

This section illustrates the effect of the coercion rules with examples.

Example: Coercion to xs:string

Consider the case where the required type (of a variable, or a function argument) is xs:string. For example, the second argument of fn:matches, which expects a regular expression. The table below illustrates the values that might be supplied, and the coercions that are applied.

Supplied ValueCoercion
"[0-9]"

None; the supplied value is an instance of the required type.

default-language()

None; the supplied value is an instance of xs:language, which is a subtype of the required type xs:string.

<a>[0-9]</a>

The supplied element node is atomized. Unless it has been schema-validated, the typed value will be an instance of xs:untypedAtomic, which is accepted when the required type is xs:string.

Supplying an element whose type annotation is (say) xs:date will fail with a type error.

xs:anyURI("urn:dummy")

Supplying an instance of xs:anyURI where the expected type is xs:string is permitted; this is one of the pairs of types where implicit casting is allowed.

["a|b"]

Supplying an array holding a single string succeeds, because the rules cause the array to be atomized, and the value after atomization is a single string.

Supplying an array holding multiple strings would fail.

 

Example: Coercion to xs:decimal?

Consider the case where the required type (of a variable, or a function argument) is xs:decimal?. For example, the first argument of fn:seconds, which expects a decimal number of seconds. The table below illustrates the values that might be supplied, and the coercions that are applied.

Supplied ValueCoercion
12.4

None; the supplied value is an instance of the required type.

()

None; an empty sequence is an instance of the required type.

42

None; the supplied value is an instance of xs:integer, which is a subtype of the required type.

math:pi()

The supplied value is an instance of xs:double, which can be converted to xs:decimal under the coercion rules.

("a", "b")[.="c"]

The supplied value is an empty sequence, which is a valid instance of the required type xs:decimal?. However, the processor may (optionally) reject this as an implausible coercion, on the grounds that it can only succeed in one special case, namely where the filter expression selects no values.

(1.5, 2.5, 3.5)

A type error is raised.

<a>3.14159</a>

The element node is atomized; unless it has been schema-validated, the result will be "3.14159" as an instance of xs:untypedAtomic. This is converted to an instance of xs:decimal following the rules of the cast as operator.

[1.5]

The array is atomized, and the result is a valid instance of the required type xs:decimal?

[]

The array is atomized, and the result is an empty sequence, which is a valid instance of the required type xs:decimal?

 

Example: Coercion to xs:positive-integer

Consider the case where the required type (of a variable, or a function argument) is xs:positive-integer. The table below illustrates the values that might be supplied, and the coercions that are applied.

Supplied ValueCoercion
12

The supplied value is of type xs:integer. Because the supplied value and the required type, xs:positiveInteger, both come under the primitive type xs:decimal, and the value 12 is within the value space of xs:positiveInteger, the value is relabeled as an xs:positiveInteger and the call succeeds.

12.1

This fails with a type error, because the xs:decimal value 12.1 is not a value in the value space of xs:positiveInteger. This is so even though casting to xs:positiveInteger would succeed.

math:pi()

This fails with a type error. A value of type xs:double is accepted where the required type is xs:decimal or xs:float, but not where it is xs:positiveInteger.

<a>1200</a>

The supplied element node is atomized. If the element has not been schema-validated, the result will be an xs:untypedAtomic item, which is successfully cast to the required type xs:positiveInteger. If the element has been validated against a schema, then coercion succeeds if the typed value would itself be acceptable, for example if it is an xs:positiveInteger, or some other xs:decimal within the value space of xs:positiveInteger.

 

Example: Coercion to a union type

Consider the first parameter of the function fn:char, whose declared type is (xs:string | xs:positiveInteger). The rules are the same as if it were a union typed declared in an imported schema.

Supplied ValueCoercion
"amp"

The supplied value is of type xs:string, which is one of the allowed types. The call therefore succeeds.

"#"

The supplied value is of type xs:string, which is one of the allowed types. As far as the coercion rules are concerned, the call therefore succeeds. Under the semantic rules for the fn:char function, however, this value is not accepted; a dynamic error (as distinct from a type error) is therefore raised.

0x25

The supplied value is of type xs:integer. Although this is not one of the allowed types, it is acceptable because coercion of the value to type xs:positiveInteger succeeds. The value is relabeled as an instance of xs:positiveInteger.

<a>0x25</a>

The supplied element node is atomized. Assuming that the node has not been schema-validated, the result is an instance of xs:untypedAtomic. The member types of the choice are tested in order. Conversion to xs:string with the value "0x25" succeeds, so the fn:char function is called supplying this string; but the function rejects this string as semantically invalid. The same would happen if the value were, say, <a>37</a>. Supplying such a value requires an explicit cast, for example fn:char( xs:positiveInteger( ./a )).

 

Example: Coercion to a choice type

Suppose the required type is (record(x as xs:decimal, y as xs:decimal, *) | record(size as enum("S", "M", "L", "XL"), *)).

Supplied ValueCoercion
{ "x": 1, "y": 2, "z": 3 }

The supplied value is an instance of the first record type: no coercion is necessary.

{ "size": "M" }

The supplied value is an instance of the second record type: no coercion is necessary.

{ "x": 1, "y": 2, "size": "XL" }

The supplied value is an instance of both record types: no coercion is necessary.

{ "x": 1e0, "y": 2e0, "size": "XL" }

The supplied value is not an instance of the first record type because the fields are of type xs:double rather than xs:decimal. It is however an instance of the second record type. It is therefore accepted as is; the fields x and y are not converted from xs:double to xs:decimal.

{ "x": 1e0, "y": 2e0, "size": "XXL" }

The supplied value is not an instance of the first record type because the fields are of type xs:double rather than xs:decimal, and it is not an instance of the second record type because the size value does not match the enumeration type. Coercion is therefore attempted to the first record type, and succeeds. The x and y fields are coerced to xs:decimal, and the size field is accepted as is.

3.5 Schema Types

[Definition: A schema type is a complex type or simple type as defined in the [XML Schema 1.0] or [XML Schema 1.1] specifications, including built-in types as well as user-defined types.]

Every schema type is either a complex type or a simple type; simple types are further subdivided into list types, union types, and atomic types (see [XML Schema 1.0] or [XML Schema 1.1] for definitions and explanations of these terms.)

A schema type can appear as a type annotation on an element or attribute node. The type annotation on an element node can be a complex type or a simple type; the type annotation on an attribute node is always a simple type. Non-instantiable types such as xs:NOTATION or xs:anyAtomicType never appear as type annotations, but their derived types can be so used. Union types never appear as type annotations; when an element or attribute is validated against a union type, the resulting type annotation will be one of the types in the transitive membership of the union type.

[Definition: An atomic type is a simple schema type whose {variety} is atomic.]

An atomic type is either a built-in atomic type (defined either in the XSD specification or in this specification), or it is a user-defined atomic type included in an imported schema.

The schema types defined in Section 2.8.3 Predefined TypesDM are summarized below.

The in-scope schema types in the static context are initialized with certain predefined schema types, including the built-in schema types in the namespace http://www.w3.org/2001/XMLSchema, which has the predefined namespace prefix xs. The schema types in this namespace are defined in [XML Schema 1.0] or [XML Schema 1.1] and augmented by additional types defined in [XQuery and XPath Data Model (XDM) 4.0]. Element and attribute declarations in the xs namespace are not implicitly included in the static context. The schema types defined in [XQuery and XPath Data Model (XDM) 4.0] are summarized below.

  1. [Definition: xs:untyped is used as the type annotation of an element node that has not been validated, or has been validated in skip mode.] No predefined schema types are derived from xs:untyped.

  2. [Definition: xs:untypedAtomic is an atomic type that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in skip mode is represented in the data model by an attribute node with the type annotationxs:untypedAtomic. No predefined schema types are derived from xs:untypedAtomic.

  3. [Definition: xs:dayTimeDuration is derived by restriction from xs:duration. The lexical representation of xs:dayTimeDuration is restricted to contain only day, hour, minute, and second components.]

  4. [Definition: xs:yearMonthDuration is derived by restriction from xs:duration. The lexical representation of xs:yearMonthDuration is restricted to contain only year and month components.]

  5. [Definition: xs:anyAtomicType is an atomic type that includes all atomic items (and no values that are not atomic). Its base type is xs:anySimpleType from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as xs:decimal and xs:string, have xs:anyAtomicType as their base type.]

    Note:

    xs:anyAtomicType will not appear as the type of an actual value in an XDM instance.

  6. [Definition: xs:error is a simple type with no value space. It is defined in Section 3.16.7.3 xs:error XS11-1 and can be used in the 3.1 Sequence Types to raise errors.]

The relationships among the schema types in the xs namespace are illustrated in Figure 2. A more complete description of the XQuery 4.0 type hierarchy can be found in Section 1.8 Type SystemFO.

Type Hierarchy Diagram

Figure 2: Hierarchy of Schema Types used in XQuery 4.0.

4 Expressions

This section discusses each of the basic kinds of expression. Each kind of expression has a name such as PathExpr, which is introduced on the left side of the grammar production that defines the expression. Since XQuery 4.0 is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.

The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [A XQuery 4.0 Grammar].

[Definition: A query consists of one or more modules.] If a query is executable, one of its modules has a Query Body containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol Expr.

Expr::=(ExprSingle ++ ",")
ExprSingle::=FLWORExpr
| QuantifiedExpr
| SwitchExpr
| TypeswitchExpr
| IfExpr
| TryCatchExpr
| OrExpr

The XQuery 4.0 operator that has lowest precedence is the comma operator, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of multiple ExprSingle operands, separated by commas.

The name ExprSingle denotes an expression that does not contain a top-level comma operator (despite its name, an ExprSingle may evaluate to a sequence containing more than one item.)

The symbol ExprSingle is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be a ExprSingle, because commas are used to separate the arguments of a function call.

After the comma, the expressions that have next lowest precedence are FLWORExpr,QuantifiedExpr, SwitchExpr, TypeswitchExpr, IfExpr, TryCatchExpr, and OrExpr. Each of these expressions is described in a separate section of this document.

4.1 Comments

Comment::="(:" (CommentContents | Comment)* ":)"
/* ws: explicit */
/* gn: comments */
CommentContents::=(Char+ - (Char* ('(:' | ':)') Char*))
/* ws: explicit */

Comments may be used to provide information relevant to programmers who read a query, either in the Prolog or in the Query Body . Comments are lexical constructs only, and do not affect query processing.

Comments are strings, delimited by the symbols (: and :). Comments may be nested.

A comment may be used anywhere ignorable whitespace is allowed (see A.3.5.1 Default Whitespace Handling).

The following is an example of a comment:

(: Houston, we have a problem :)

4.2 Primary Expressions

[Definition: Primary expressions are the basic primitives of the language. They include literals, variable references, context value references, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Node Constructors are described in 4.12 Node Constructors.Map and Array Constructors are described in 4.14.1 Maps and 4.14.2 Arrays. String Constructors are described in 4.9.3 String Constructors.

PrimaryExpr::=Literal
| VarRef
| ParenthesizedExpr
| ContextValueRef
| FunctionCall
| OrderedExpr
| UnorderedExpr
| NodeConstructor
| FunctionItemExpr
| MapConstructor
| ArrayConstructor
| StringTemplate
| StringConstructor
| UnaryLookup
FunctionItemExpr::=NamedFunctionRef | InlineFunctionExpr

4.2.1 Literals

Literal::=NumericLiteral | StringLiteral

[Definition: A literal is a direct syntactic representation of an atomic item.] XQuery 4.0 supports two kinds of literals: numeric literals and string literals.

4.2.1.1 Numeric Literals

Changes in 4.0  

  1. Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability.   [Issue 429 PR 433 25 April 2023]

NumericLiteral::=IntegerLiteral | HexIntegerLiteral | BinaryIntegerLiteral | DecimalLiteral | DoubleLiteral
IntegerLiteral::=Digits
/* ws: explicit */
HexIntegerLiteral::="0x" HexDigits
/* ws: explicit */
BinaryIntegerLiteral::="0b" BinaryDigits
/* ws: explicit */
DecimalLiteral::=("." Digits) | (Digits "." Digits?)
/* ws: explicit */
DoubleLiteral::=(("." Digits) | (Digits ("." Digits?)?)) [eE] [+-]? Digits
/* ws: explicit */
Digits::=DecDigit ((DecDigit | "_")* DecDigit)?
/* ws: explicit */
DecDigit::=[0-9]
/* ws: explicit */
HexDigits::=HexDigit ((HexDigit | "_")* HexDigit)?
/* ws: explicit */
HexDigit::=[0-9a-fA-F]
/* ws: explicit */
BinaryDigits::=BinaryDigit ((BinaryDigit | "_")* BinaryDigit)?
/* ws: explicit */
BinaryDigit::=[01]
/* ws: explicit */

The value of a numeric literal is determined as follows (taking the rules in order):

  1. Underscore characters are stripped out. Underscores may be included in a numeric literal to aid readability, but have no effect on the value. For example, 1_000_000 is equivalent to 1000000.

    Note:

    Underscores must not appear at the beginning or end of a sequence of digits, only in intermediate positions. Multiple adjacent underscores are allowed.

  2. A HexIntegerLiteral represents a non-negative integer expressed in hexadecimal: for example 0xffff represents the integer 65535, and 0xFFFF_FFFF represents the integer 4294967295.

  3. A BinaryIntegerLiteral represents a non-negative integer expressed in binary: for example 0b101 represents the integer 5, and 0b1111_1111 represents the integer 255.

  4. The value of a numeric literal containing no . and no e or E character is an atomic item of type xs:integer; the value is obtained by casting from xs:string to xs:integer as specified in Section 21.2 Casting from xs:string and xs:untypedAtomicFO.

  5. The value of a numeric literal containing . but no e or E character is an atomic item of type xs:decimal; the value is obtained by casting from xs:string to xs:decimal as specified in Section 21.2 Casting from xs:string and xs:untypedAtomicFO.

  6. The value of a numeric literal containing an e or E character is an atomic item of type xs:double; the value is obtained by casting from xs:string to xs:double as specified in Section 21.2 Casting from xs:string and xs:untypedAtomicFO.

Note:

The value of a numeric literal is always non-negative. An expression may appear to include a negative number such as -1, but this is technically an arithmetic expression comprising a unary minus operator followed by a numeric literal.

Note:

The effect of the above rules is that in the case of an integer or decimal literal, a dynamic error [err:FOAR0002]FO40 will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see Section 4.2 Arithmetic operators on numeric valuesFO for details.)

The limits of numeric datatypes are specified in 6.3 Data Model Conformance.

Here are some examples of numeric literals:

  • 12 denotes the xs:integer value twelve.

  • 1_000_000 denotes the xs:integer value one million.

  • 12.5 denotes the xs:decimal value twelve and one half.

  • 3.14159_26535_89793e0 is an xs:double value representing the mathematical constant π to 15 decimal places.

  • 125E2 denotes the xs:double value twelve thousand, five hundred.

  • 0xffff denotes the xs:integer value 65535.

  • 0b1000_0001 denotes the xs:integer value 129.

4.2.1.2 String Literals
StringLiteral::=AposStringLiteral | QuotStringLiteral
/* ws: explicit */
AposStringLiteral::="'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'"
/* ws: explicit */
QuotStringLiteral::='"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"'
/* ws: explicit */
PredefinedEntityRef::="&" ("lt" | "gt" | "amp" | "quot" | "apos") ";"
/* ws: explicit */
CharRef::=[http://www.w3.org/TR/REC-xml#NT-CharRef]XML
/* xgc: xml-version */
EscapeQuot::='""'
/* ws: explicit */
EscapeApos::="''"
/* ws: explicit */

The value of a string literal is an atomic item whose type is xs:string and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.

[Definition: A predefined entity reference is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.] Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XPath and XQuery are as follows:

Entity ReferenceCharacter Represented
&lt;<
&gt;>
&amp;&
&quot;"
&apos;'

[Definition: A character reference is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal codepoint.] For example, the character U+20AC (EURO SIGN, ) can be represented by the character reference &#8364; or &#x20ac;. Character references are normatively defined in Section 4.1 of the XML specification (it is implementation-defined whether the rules in [XML 1.0] or [XML 1.1] apply.) A static error [err:XQST0090] is raised if a character reference does not identify a valid character in the version of XML that is in use.

Here are some examples of string literals:

  • "He said, ""I don't like it.""" denotes a string containing two quotation marks and one apostrophe.

  • "Ben &amp; Jerry&apos;s" denotes the xs:string value "Ben & Jerry's".

  • "&#8364;99.50" denotes the xs:string value "€99.50".

  • In XQuery, the string literal "&lt;" denotes a string of length 1 containing the single character "<". In XPath, the string literal "&lt;" denotes a string of length 4 containing the four characters "&", "l", "t", ";". (However, when the XPath expression is embedded in an XML document, the sequence "&lt;" will typically have already been converted to "<" by the XML parser.)

Note:

When XPath or XQuery expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, or in string literals in a host language such as Java or C#, then additional escaping may be needed.

Note:

Fixed string values can also be written as string templates: see 4.9.2 String Templates. A string template with no enclosed expressions, such as `Jamaica` evaluates to the same value as the string literals "Jamaica" or 'Jamaica'. A string template can contain both single and double quotation marks: `He said: "I don't like it"`. However, there there are some subtle differences:

  • In string literals, the treatment of character and entity references such as &amp; varies between XQuery and XPath; in string templates, such references are not expanded in either language.

  • String templates can only be used where an expression is expected. String literals are also used in some non-expression contexts, for example in defining an enumeration type: see 3.2.6 Enumeration Types.

  • Curly brackets (U+007B (LEFT CURLY BRACKET, {) and U+007D (RIGHT CURLY BRACKET, }) ) and backticks (U+0060 (GRAVE ACCENT, BACKTICK, `) ) have a reserved meaning in string templates.

4.2.1.3 Constants of Other Types

The xs:boolean values true and false can be constructed by calls to the system functionsfn:true() and fn:false(), respectively.

Values of other simple types can be constructed by calling the constructor function for the given type. The constructor functions for XML Schema built-in types are defined in Section 20.1 Constructor functions for XML Schema built-in atomic typesFO. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:

  • xs:integer("12") returns the integer value twelve.

  • xs:date("2001-08-25") returns an item whose type is xs:date and whose value represents the date 25th August 2001.

  • xs:dayTimeDuration("PT5H") returns an item whose type is xs:dayTimeDuration and whose value represents a duration of five hours.

Constructor functions can also be used to create special values that have no literal representation, as in the following examples:

  • xs:float("NaN") returns the special floating-point value, "Not a Number."

  • xs:double("INF") returns the special double-precision value, "positive infinity."

Constructor functions are available for all simple types, including union types. For example, if my:dt is a user-defined union type whose member types are xs:date, xs:time, and xs:dateTime, then the expression my:dt("2011-01-10") creates an atomic item of type xs:date. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.

It is also possible to construct values of various types by using a cast expression. For example:

  • 9 cast as hatsize returns the atomic item 9 whose type is hatsize.

4.2.2 Variable References

VarRef::="$" EQName
EQName::=QName | URIQualifiedName

[Definition: A variable reference is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their expanded QNames are equal (as defined by the eq operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.

Every variable reference must match a name in the in-scope variables.

Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a static error [err:XPST0008] to reference a variable that is not in scope. If a variable is bound in the static context for an expression, that variable is in scope for the entire expression except where it is occluded by another binding that uses the same name within that scope.

A reference to a variable that was declared external, but was not bound to a value by the external environment, raises a dynamic error [err:XPDY0002].

At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.

4.2.3 Context Value References

ContextValueRef::="."

A context value reference evaluates to the context value.

In many syntactic contexts, the context value will be a single item. For example this applies on the right-hand side of the / or ! operators, or within a Predicate.

If the context value is absentDM, a context value reference raises a type error [err:XPDY0002].

Note:

Being absent is not the same thing as being empty.

4.2.4 Parenthesized Expressions

ParenthesizedExpr::="(" Expr? ")"

Parentheses may be used to override the precedence rules. For example, the expression (2 + 4) * 5 evaluates to thirty, since the parenthesized expression (2 + 4) is evaluated first and its result is multiplied by five. Without parentheses, the expression 2 + 4 * 5 evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.

Empty parentheses are used to denote an empty sequence, as described in 4.7.1 Sequence Concatenation.

4.2.5 Enclosed Expressions

EnclosedExpr::="{" Expr? "}"

[Definition: An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly brackets.] [Definition: In an enclosed expression, the optional expression enclosed in curly brackets is called the content expression.] If the content expression is not provided explicitly, the content expression is ().

Note:

Despite the name, an enclosed expression is not actually an expression in its own right; rather it is a construct that is used in the grammar of many other expressions.

4.3 Postfix Expressions

PostfixExpr::=PrimaryExpr | FilterExpr | DynamicFunctionCall | LookupExpr | FilterExprAM
FilterExpr::=PostfixExprPredicate
DynamicFunctionCall::=PostfixExprPositionalArgumentList
LookupExpr::=PostfixExprLookup

A postfix expression takes one of the following forms:

  • [Definition: A filter expression is an expression in the form E1[E2]: its effect is to return those items from the value of E1 that satisfy the predicate in E2.]

    Filter expressions are described in 4.4 Filter Expressions.

    An example of a filter expression is (1 to 100)[. mod 2 = 0] which returns all even numbers in the range 1 to 100.

    The base expression E1 can itself be a postfix expression, so multiple predicates are allowed, in the form E1[E2][E3][E4].

  • An expression (other than a raw EQName) followed by an argument list in parentheses (that is, E1(E2, E3, ...)) is referred to as a dynamic function call. Its effect is to evaluate E1 to obtain a function, and then call that function, with E2, E3, ... as arguments. Dynamic function calls are described in 4.5.2.1 Dynamic Function Calls.

    An example of a dynamic function call is $f("a", 2) where the value of variable $f must be a function item.

  • A lookup-expression takes the form E1?K, where E1 is an expression returning a sequence of maps or arrays, and K is a key specifier, which indicates which entries in a map, or members in an array, should be selected.

    Lookup expressions are described in 4.14.3.1 Postfix Lookup Expressions.

    An example of a lookup expression is $emp?name, where the value of variable $emp is a map, and the string "name" is the key of one of the entries in the map.

Postfix expressions are evaluated from left-to-right. For example, the expression $E1[E2]?(E3)(E4) is evaluated by first evaluating the filter expression $E1[E2] to produce a sequence of maps and arrays (say $S), then evaluating the lookup expression $S?(E3) to produce a function item (say $F), then evaluating the dynamic function call $F(E4) to produce the final result.

Note:

The grammar for postfix expressions is defined here in a way designed to link clearly to the semantics of the different kinds of expression. For parsing purposes, the equivalent production rule:

PostfixExpr := PrimaryExpr (Predicate | PositionalArgumentList | Lookup)*

(as used in XPath 3.1) is probably more convenient.

4.4 Filter Expressions

Changes in 4.0  

  1. The value of a predicate in a filter expression can now be a sequence of integers.   [Issue 816 PR 996 6 February 2024]

FilterExpr::=PostfixExprPredicate
Predicate::="[" Expr "]"

A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.

Note:

Where the expression before the square brackets is a ReverseStep or ForwardStep, the expression is technically not a filter expression but an AxisStep. There are minor differences in the semantics: see 4.6.5 Predicates within Steps

Here are some examples of filter expressions:

  • Given a sequence of products in a variable, return only those products whose price is greater than 100.

    $products[price gt 100]
  • List all the integers from 1 to 100 that are divisible by 5. (See 4.7.1 Sequence Concatenation for an explanation of the to operator.)

    (1 to 100)[. mod 5 eq 0]
  • The result of the following expression is the integer 25:

    (21 to 29)[5]
  • The following example returns the fifth through ninth items in the sequence bound to variable $orders.

    $orders[5 to 9]
  • The following example illustrates the use of a filter expression as a step in a path expression. It returns the last chapter or appendix within the book bound to variable $book:

    $book/(chapter | appendix)[last()]

For each item in the input sequence, the predicate expression is evaluated using an inner focus, defined as follows: The context value is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context value within the input sequence.

For each item in the input sequence, the result of the predicate expression is coerced to an xs:boolean value, called the predicate truth value, as described below. Those items for which the predicate truth value is true are retained, and those for which the predicate truth value is false are discarded.

[Definition: The predicate truth value of a value $V is the result of the expression if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V).]

Expanding this definition, the predicate truth value can be obtained by applying the following rules, in order:

  1. If the value V of the predicate expression is a sequence whose first item is an instance of the type xs:numeric, then:

    1. V must be an instance of the type xs:numeric+ (that is, every item in V must be numeric). A type error [err:FORG0006]FO40 is raised if this is not the case.

    2. The predicate truth value is true if V is equal (by the = operator) to the context position, and is false otherwise.

    In effect this means that an item in the input sequence is selected if its position in the sequence is equal to one or more of the numeric values in the predicate. For example, the predicate [3 to 5] is true for the third, fourth, and fifth items in the input sequence.

    [Definition: A predicate whose predicate expression returns a value of type xs:numeric+ is called a numeric predicate.]

    Note:

    It is possible, though not generally useful, for the value of a numeric predicate to depend on the focus, and thus to differ for different items in the input sequence. For example, the predicate [xs:integer(@seq)] selects those items in the input sequence whose @seq attribute is numerically equal to their position in the input sequence.

    It is also possible, and again not generally useful, for the value of the predicate to be numeric for some items in the input sequence, and boolean for others. For example, the predicate [@special otherwise last()] is true for an item that either has an @special attribute, or is the last item in the input sequence.

    Note:

    The truth value of a numeric predicate does not depend on the order of the numbers in V. The predicates [ 1, 2, 3 ] and [ 3, 2, 1 ] have exactly the same effect. The items in the result of a filter expression always retain the ordering of the input sequence.

    Note:

    The truth value of a numeric predicate whose value is non-integral or non-positive is always false.

    Note:

    Beware that using boolean operators (and, or, not()) with numeric values may not have the intended effect. For example the predicate [1 or last()] selects every item in the sequence, because or operates on the effective boolean value of its operands. The required effect can be achieved with the predicate [1, last()].

  2. Otherwise, the predicate truth value is the effective boolean value of the predicate expression.

4.5 Functions

Functions in XQuery 4.0 arise in two ways:

The functions defined by a statically known function definition can be invoked using a static function call. Function items corresponding to these definitions can also be obtained, as dynamic values, by evaluating a named function reference. Function items can also be obtained using the fn:function-lookup function: in this case the function name and arity do not need to be known statically, and the function definition need not be present in the static context, so long as it is in the dynamic context.

Static and dynamic function calls are described in the following sections.

4.5.1 Static Function Calls

The static context for an expression includes a set of statically known function definitions. Every function definition in the static context has a name (which is an expanded QName) and an arity range, which is a range of permitted arities for calls on that function. Two function definitions having the same name must not have overlapping arity ranges. This means that for a given static function call, it is possible to identify the target function definition in the static context unambiguously from knowledge of the function name and the number of supplied arguments.

A static function call is bound to a function definition in the static context by matching the name and arity. If the function call has P positional arguments followed by K keyword arguments, then the required arity is P+K, and the static context must include a function definition whose name matches the expanded QName in the function call, and whose arity range includes this required arity. This is the function chosen to be called. The result of the function is obtained by evaluating the expression that forms its implementation, with a dynamic context that provides values for all the declared parameters, initialized as described in 4.5.1.2 Evaluating Static Function Calls below.

Similarly, a function reference of the form f#N binds to a function definition in the static context whose name matches f where MinP ≤ N and MaxP ≥ N. The result of evaluating a function reference is a function item which can be called using a dynamic function call. Function items are never variadic and their arguments are always supplied positionally. For example, the function reference fn:concat#3 returns a function item with arity 3, which is always called by supplying three positional arguments, and whose effect is the same as a static call on fn:concat with three positional arguments.

The detailed rules for evaluating static function calls and function references are defined in subsequent sections.

4.5.1.1 Static Function Call Syntax

Changes in 4.0  

  1. Keyword arguments are allowed on static function calls, as well as positional arguments.   [Issue 155 PR 159 30 September 2020]

FunctionCall::=EQNameArgumentList
/* xgc: reserved-function-names */
/* gn: parens */
ArgumentList::="(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
PositionalArguments::=(Argument ++ ",")
Argument::=ExprSingle | ArgumentPlaceholder
ArgumentPlaceholder::="?"
KeywordArguments::=(KeywordArgument ++ ",")
KeywordArgument::=EQName ":=" Argument

[Definition: A static function call consists of an EQName followed by a parenthesized list of zero or more arguments.]

The argument list consists of zero or more positional arguments, followed by zero or more keyword arguments.

[Definition: An argument to a function call is either an argument expression or an ArgumentPlaceholder (?); in both cases it may either be supplied positionally, or identified by a name (called a keyword).]

This section is concerned with static function calls in which none of the arguments are ArgumentPlaceholders. Calls using one or more ArgumentPlaceholders are covered in the section 4.5.2.3 Partial Function Application.

If the function name supplied in a static function call is an unprefixed lexical QName, it is expanded using the default function namespace in the static context.

The expanded QName used as the function name and the number of arguments used in the static function call (the required arity) must match the name and arity range of a function definition in the static context using the rules defined in the previous section; if there is no match, a static error is raised [err:XPST0017].

Evaluation of static function calls is described in 4.5.1.2 Evaluating Static Function Calls .

Since the arguments of a function call are separated by commas, any argument expression that contains a top-level comma operator must be enclosed in parentheses. Here are some illustrative examples of static function calls:

  • my:three-argument-function(1, 2, 3) denotes a static function call with three positional arguments. The corresponding function declaration must define at least three parameters, and may define more, provided they are optional.

  • my:two-argument-function((1, 2), 3) denotes a static function call with two arguments, the first of which is a sequence of two values. The corresponding function declaration must define at least two parameters, and may define more, provided they are optional.

  • my:two-argument-function(1, ()) denotes a static function call with two arguments, the second of which is an empty sequence.

  • my:one-argument-function((1, 2, 3)) denotes a static function call with one argument that is a sequence of three values.

  • my:one-argument-function(( )) denotes a static function call with one argument that is an empty sequence.

  • my:zero-argument-function( ) denotes a static function call with zero arguments.

  • lang(node := $n, language := 'de') is a static function call with two keyword arguments. The corresponding function declaration defines two parameters, a required parameter language and an optional parameter node. This call supplies values for both parameters. It is equivalent to the call fn:lang('de', $n). Note that the keyword arguments are in a different order from the parameter declarations.

  • sort(//employee, key := fn($e) { xs:decimal($e/salary) }) is a static function call with one positional argument and one keyword argument. The corresponding function declaration defines three parameters, a required parameter $input, an optional parameter $collation, and an optional parameter $key This call supplies values for the first and third parameters, leaving the second parameter ($collation) to take its default value. The default value of the $collation parameter is given as fn:default-collation(), so the value supplied to the function is the default collation from the dynamic context of the caller. It is equivalent to the call fn:sort(//employee, fn:default-collation(), fn($e) { xs:decimal($e/salary) }).

An EQName in a KeywordArgument is expanded to a QName value; if there is no prefix, then the name is in no namespace (otherwise the prefix is resolved in the usual way). The keywords used in a function call (after expansion to QNames) must be distinct [err:XPST0017]; [err:XPST0017].

4.5.1.2 Evaluating Static Function Calls

This section applies to static function calls where none of the arguments is an ArgumentPlaceholder. For function calls involving placeholders, see 4.5.2.3 Partial Function Application.

When a static function call FC is evaluated with respect to a static context SC and a dynamic context DC, the result is obtained as follows:

  1. The function definitionFD to be used is found in the statically known function definitions of SC.

    The required arity is the total number of arguments in the function call, including both positional and keyword arguments.

    There can be at most one function definitionFD in the statically known function definitions component of SC whose function name matches the expanded QName in FC and whose arity range includes the arity of FC’s ArgumentList.

    If there is no such function definition, a static error [err:XPST0017] is raised.

  2. Each parameter in the function definitionFD is matched to an argument expression as follows:

    1. If there are N positional arguments in the function call FC, then the corresponding argument expressions are matched pairwise to the first N parameters in the declaration. For this purpose the required parameters and optional parameters in FD are concatenated into a single list, in order.

    2. Any keyword arguments in FC are then matched to parameters (whether required or optional) in FD by comparing the keyword used in FC with the paramater name declared in FD. Each keyword must match the name of a declared parameter [err:XPST0017], and this must be one that has not already been matched to a positional argument. [err:XPST0017].

    3. If any required parameter has not been matched to any argument in FC by applying the above rules, a static error is reported [err:XPST0017]

    4. If any optional parameter has not been matched to any argument in FC by applying the above rules, then the parameter is matched to the default value expression for that parameter in FD.

  3. Each argument expression established by the above rules is evaluated with respect to DC. The order of argument evaluation is implementation dependent and it is not required that an argument be evaluated if the function body can be evaluated without evaluating that argument.

    Note:

    All argument expressions, including default value expressions, are evaluated in the dynamic context of the function call. It is therefore possible to use a default value expression such as ., or /, or fn:current-dateTime(), whose value depends on the dynamic context of the function call.

    If the expression used for the default value of a parameter has no dependencies on the dynamic context, then an implementation may choose to reuse the same value on repeated function calls rather than re-evaluating it on each function call.

    Note:

    This is relevant, for example, if the expression constructs new nodes.

  4. The result of evaluating the argument expression is converted to the required type (the declared type associated with the corresponding parameter in the function declaration, defaulting to item()*) by applying the coercion rules.

    This applies both to explicitly supplied arguments, and to values obtained by evaluating default value expressions. In both cases a type error will be raised if the value (after coercion) does not match the required type.

  5. The result of the function call is obtained as follows:

    • FD’s body is invoked in an implementation-dependent way. The processor makes the following information available to that invocation:

      • The converted argument values;

      • If the function is context dependent, the static context SC and dynamic context DC of the function call.

    • The result is converted to the required type (the declared return type in the function declaration, defaulting to item()*) by applying the coercion rules.

      The result of applying the coercion rules is either an instance of FD’s return type or a dynamic error. This result is then the result of evaluating FC.

      Note:

      A host language may define alternative rules for processing the result, especially in the case of external functions implemented using a non-XDM type system.

    • Errors raised by system functions are defined in [XQuery and XPath Functions and Operators 4.0].

    • Errors raised by external functions are implementation-defined (see 2.3.6 Consistency Constraints).

    Example: A System Function

    The following function call uses the function Section 2.1.5 fn:base-uriFO. Use of SC and DC and errors raised by this function are all defined in [XQuery and XPath Functions and Operators 4.0].

    base-uri()

4.5.2 Function Items

A function item is an XDM value that can be bound to a variable, or manipulated in various ways by XQuery 4.0 expressions. The most significant such expression is a dynamic function call, which supplies values of arguments and evaluates the function to produce a result.

The syntax of dynamic function calls is defined in 4.5.2.1 Dynamic Function Calls.

A number of constructs can be used to produce a function item, notably:

These constructs are described in detail in the following sections, or in [XQuery and XPath Functions and Operators 4.0].

4.5.2.1 Dynamic Function Calls
DynamicFunctionCall::=PostfixExprPositionalArgumentList
PositionalArgumentList::="(" PositionalArguments? ")"
PositionalArguments::=(Argument ++ ",")
Argument::=ExprSingle | ArgumentPlaceholder
ArgumentPlaceholder::="?"

[Definition: A dynamic function call consists of a base expression that returns the function and a parenthesized list of zero or more arguments (argument expressions or ArgumentPlaceholders).]

A dynamic function call is evaluated as described in 4.5.2.2 Evaluating Dynamic Function Calls.

The following are examples of some dynamic function calls:

  • This example calls the function contained in $f, passing the arguments 2 and 3:

    $f(2, 3)
  • This example fetches the second item from sequence $f, treats it as a function and calls it, passing an xs:string argument:

    $f[2]("Hi there")
  • This example calls the function $f passing no arguments, and filters the result with a positional predicate:

    $f()[2]

Note:

Arguments in a dynamic function call are always supplied positionally.

4.5.2.2 Evaluating Dynamic Function Calls

This section applies to dynamic function calls whose arguments do not include an ArgumentPlaceholder. For function calls that include a placeholder, see 4.5.2.3 Partial Function Application.

[Definition: A dynamic function call is an expression that is evaluated by calling a function item, which is typically obtained dynamically.]

When a dynamic function call FC is evaluated, the result is obtained as follows:

  1. The function itemFI to be called is obtained by evaluating the base expression of the function call. If this yields a sequence consisting of a single function item whose arity matches the number of arguments in the ArgumentList, let FI denote that function item. Otherwise, a type error is raised [err:XPTY0004].

    Note:

    Keyword arguments are not allowed in a dynamic function call.

  2. Argument expressions are evaluated, producing argument values. The order of argument evaluation is implementation-dependent and an argument need not be evaluated if the function body can be evaluated without evaluating that argument.

  3. Each argument value is converted to the corresponding parameter type in FI’s signature by applying the coercion rules, resulting in a converted argument value

  4. If FI is a map, it is evaluated as described in 4.14.1.2 Maps as Functions.

  5. If FI is an array, it is evaluated as described in 4.14.2.2 Arrays as Functions.

  6. If FI’s body is an XQuery 4.0 expression (for example, if FI is a user-defined function or an anonymous function, or a partial application of such a function):

    1. FI’s body is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the module that contains the FunctionBody, and making the following changes:

      • The focus (context value, context position, and context size) is absentDM.

      • In the variable values component of the dynamic context, each converted argument value is bound to the corresponding parameter name.

        When this is done, the converted argument values retain their dynamic types, even where these are subtypes of the declared parameter types. For example, a function with a parameter $p of type xs:decimal can be called with an argument of type xs:integer, which is derived from xs:decimal. During the processing of this function call, the value of $p inside the body of the function retains its dynamic type of xs:integer.

      • FI’s nonlocal variable bindings are also added to the variable values. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.)

    2. The value returned by evaluating the function body is then converted to the declared return type of FI by applying the coercion rules. The result is then the result of evaluating FC.

      As with argument values, the value returned by a function retains its dynamic type, which may be a subtype of the declared return type of FI. For example, a function that has a declared return type of xs:decimal may in fact return a value of dynamic type xs:integer.

    Example: Derived Types and Nonlocal Variable Bindings

    $incr is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both xs:decimal, the more specific type xs:integer is preserved in both cases.

    let $incr := 1
    let $f := function($i as xs:decimal) as xs:decimal { $i + $incr }
    return $f(5)

     

    Example: Using the Context Value in an Anonymous Function

    The following example will raise a type error [err:XPDY0002]:

    let $vat := function() { @vat + @price }
    return doc('wares.xml')/shop/article/$vat()

    Instead, the context value can be used as an argument to the anonymous function:

    let $vat := function($art) { $art/@vat + $art/@price }
    return doc('wares.xml')/shop/article/$vat(.)

    Alternatively, the value can be referenced as a nonlocal variable binding:

    let $ctx := doc('wares.xml')/shop/article
    let $vat := function() { for $a in $ctx return $a/@vat + $a/@price }
    return $vat()

    Finally, a focus function can be used. This binds the value of the argument to the context value within the function body:

    let $vat := function { @vat + @price }
    return $vat(doc('wares.xml')/shop/article)
  7. If the implementation of FI is not an XQuery 4.0 expression (for example, FI is a system functionor an external function, the body of the function is evaluated, and the result is converted to the declared return type, in the same way as for a static function call (see 4.5.1.1 Static Function Call Syntax).

    Errors may be raised in the same way.

4.5.2.3 Partial Function Application

[Definition: A static or dynamic function call is a partial function application if one or more arguments is an ArgumentPlaceholder.]

The rules for partial function application in static function calls and dynamic function calls have a great deal in common, but they are stated separately below for clarity.

In each case, the result of a partial function application is a function item, whose arity is equal to the number of placeholders in the call.

More specifically, the result of the partial function application is a partially applied function. [Definition: A partially applied function is a function created by partial function application.]

For static function calls, the result is obtained as follows:

  1. The function definitionFD to be partially applied is determined in the same way as for a static function call without placeholders, as described in 4.5.1.1 Static Function Call Syntax. For this purpose an ArgumentPlaceholder contributes to the count of arguments.

  2. The parameters of FD are classified into three categories:

    • Parameters that map to a placeholder, referred to as placeholder parameters.

    • Parameters for which an explicit value is given in the function call (either positionally or by keyword), referred to as explicitly supplied parameters.

    • Parameters (which are necessarily optional parameters) for which no corresponding argument is supplied, either as a placeholder or with an explicit value. These are referred to as defaulted parameters.

    Note:

    A partial function application need not have any explicitly supplied parameters. For example, the partial function application fn:string(?) is allowed; it has exactly the same effect as the named function reference fn:string#1.

  3. Explicitly supplied parameters and defaulted parameters are evaluated and converted to the required type using the rules for a static function call. This may result in an error being raised.

    A type error is raised if any of the explicitly supplied or defaulted parameters, after applying the coercion rules, does not match the required type of the corresponding parameter.

    In addition, a dynamic error may be raised if any of the explicitly supplied or defaulted parameters does not match other constraints on the value of that parameter (for example, if the value supplied for a parameter expecting a regular expression is not a valid regular expression); or if the processor is able to establish that evaluation of the resulting function will fail for any other reason (for example, if an error is raised while evaluating a subexpression in the function body that depends only on explicitly supplied and defaulted parameters).

    In all cases the error code is the same as for a static function call supplying the same invalid value(s).

    In the particular case where all the supplied arguments are placeholders, the error behavior should be the same as for an equivalent named function reference: for example, fn:id#1 fails if there is no context node, and fn:id(?)should fail likewise.

  4. The result is a partially applied function having the following properties (which are defined in Section 2.9.4 Function ItemsDM):

    • name: The name of FD if all parameters map to placeholders, that is, if the partial function application is equivalent to the corresponding named function reference. Otherwise, the name is absent.

    • identity: A new function identity distinct from the identity of any other function item.

    • arity: The number of placeholders in the function call.

    • parameter names: The names of the parameters of FD that have been identified as placeholder parameters, retaining the order in which the placeholders appear in the function call.

      Note:

      A partial function application can be used to change the order of parameters, for example fn:contains(substring := ?, value := ?) returns a function item that is equivalent to fn:contains#2, but with the order of arguments reversed.

    • signature: The parameters in the returned function are the parameters of FD that have been identified as placeholder parameters, retaining the order in which the placeholders appear in the function call. The result type of the returned function is the same as the result type of FD.

      An implementation which can determine a more specific signature (for example, through use of type analysis) is permitted to do so.

    • body: The body of FD.

    • captured context: The static and dynamic context of the function call, augmented, for each explicitly supplied parameter and each defaulted parameter, with a binding of the converted argument value to the corresponding parameter name.

    Example: Partial Application of a System Function

    The following partial function application creates a function item that computes the sum of squares of a sequence.

    let $sum-of-squares := fold-right(?, 0, function($a, $b) { $a*$a + $b })
    return $sum-of-squares(1 to 3)

    $sum-of-squares is an anonymous function. It has one parameter, named $seq, which is taken from the corresponding parameter in fn:fold-right (the other two parameters are fixed). The implementation is the implementation of fn:fold-right, which is a context-independent system function. The nonlocal bindings contain the fixed bindings for the second and third parameters of fn:fold-right.

For dynamic function calls, the result is obtained as follows:

  1. The function itemFI to be partially applied is determined in the same way as for a dynamic function call without placeholders, as described in 4.5.2.1 Dynamic Function Calls. For this purpose an ArgumentPlaceholder contributes to the count of arguments.

  2. The parameters of FI are classified into two categories:

    • Parameters that map to a placeholder, referred to as placeholder parameters.

    • Parameters for which an explicit value is given in the function call, referred to as supplied parameters.

    Note:

    A partial function application need not have any explicitly supplied parameters. For example, if $f is a function with arity 2, then the partial function application $f(?, ?) returns a function that has exactly the same effect as $f.

  3. Arguments corresponding to supplied parameters are evaluated and converted to the required type of the parameter, using the rules for dynamic function calls.

    A type error is raised if any of the supplied parameters, after applying the coercion rules, does not match the required type.

    In addition, a dynamic error may be raised if any of the supplied parameters does not match other constraints on the value of that parameter (for example, if the value supplied for a parameter expecting a regular expression is not a valid regular expression); or if the processor is able to establish that evaluation of the resulting function will fail for any other reason (for example, if an error is raised while evaluating a subexpression in the function body that depends only on explicitly supplied parameters).

    In both cases the error code is the same as for a dynamic function call supplying the same invalid value.

  4. The result of the partial function application is a partially applied function with the following properties (which are defined in Section 2.9.4 Function ItemsDM):

    • name: Absent.

    • arity: The number of placeholders in the function call.

    • parameter names: The names of parameters in FI that have been identified as placeholder parameters, in order.

      Note:

      In a dynamic partial function application, argument keywords are not available, so it is not possible to change the order of parameters.

    • signature: The signature of FI, removing the types of supplied parameters. An implementation which can determine a more specific signature (for example, through use of type analysis) is permitted to do so.

    • body: The body of FI.

    • captured context: the captured context of FI, augmented, for each supplied parameter, with a binding of the converted argument value to the corresponding parameter name.

    Example: Partial Application of an Anonymous Function

    In the following example, $f is an anonymous function, and $paf is a partially applied function created from $f.

    let $f := function($seq, $delim) { fold-left($seq, "", concat(?, $delim, ?)) }
    let $paf := $f(?, ".")
    return $paf(1 to 5)

    $paf is also an anonymous function. It has one parameter, named $delim, which is taken from the corresponding parameter in $f (the other parameter is fixed). The implementation of $paf is the implementation of $f, which is fn:fold-left($seq, "", fn:concat(?, $delim, ?)). This implementation is associated with the SC and DC of the original expression in $f. The nonlocal bindings associate the value "." with the parameter $delim.

Partial function application never returns a map or an array. If $f is a map or an array, then $f(?) is a partial function application that returns a function, but the function it returns is neither a map nor an array.

Example: Partial Application of a Map

The following partial function application converts a map to an equivalent function that is not a map.

let $a := { "A": 1, "B": 2 }(?)
return $a("A")
4.5.2.4 Named Function References
NamedFunctionRef::=EQName "#" IntegerLiteral
/* xgc: reserved-function-names */
EQName::=QName | URIQualifiedName

[Definition: A named function reference is an expression (written name#arity) which evaluates to a function item, the details of the function item being based on the properties of a function definition in the static context.]

The name and arity of the required function are known statically.

If the EQName is a lexical QName, it is expanded using the default function namespace in the static context.

The expanded QName and arity must correspond to a function definition present in the static context. More specifically, for a named function reference F#N, there must be a function definition in the statically known function definitions whose name matches F, and whose arity range includes N. Call this function definitionFD.

If FD is context dependent for the given arity, then the returned function item has a captured context comprising the static and dynamic context of the named function reference.

Note:

In practice, it is necessary to retain only those parts of the static and dynamic context that can affect the outcome. These means it is unnecessary to retain parts of the context that no system function depends on (for example, local variables), or parts that are invariant within an execution scope (for example, the implicit timezone).

Example: A Context-Dependent Named Function Reference

Consider:

let $f := <foo/>/fn:name#0 return <bar/>/$f()

The function fn:name(), with no arguments, returns the name of the context node. The function item delivered by evaluating the expression fn:name#0 returns the name of the element that was the context node at the point where the function reference was evaluated (that is, the <foo> element). This expression therefore returns "foo", not "bar".

An error is raised if the identified function depends on components of the static or dynamic context that are not present, or that have unsuitable values. For example [err:XPDY0002] is raised for the expression fn:name#0 if the context item is absent, and [err:FODC0001]FO is raised for the call fn:id#1 if the context item is not a node in a tree that is rooted at a document node. The error that is raised is the same as the error that would be raised by the corresponding function if called with the same static and dynamic context.

If the expanded QName and arity in a named function reference do not match the name and arity range of a function definition in the static context, a static error is raised [err:XPST0017].

The value of a NamedFunctionRef is a function itemFI obtained from FD as follows:

  • name: The name of FD.

  • identity:

    • If FD is context dependent for the given arity, then a new function identity distinct from the identity of any other function item.

      Note:

      In the general case, a function reference to a context-dependent function will produce different results every time it is evaluated, because the resulting function item has a captured context (see Section 2.9.4 Function ItemsDM) that includes the dynamic context of the particular evaluation. Optimizers, however, are allowed to detect cases where the captured context happens to be the same, or where any variations are immaterial, and where it is therefore safe to return the same function item each time. This might be the case, for example, where the only context dependency of a function is on the default collation, and the default collation for both evaluations is known to be the same.

    • Otherwise, a function identity that is the same as that produced by the evaluation of any other named function reference with the same function name and arity.

      This rule applies even across different execution scopesFO: for example if a parameter to a call to fn:transform is set to the result of the expression fn:abs#1, then the function item passed as the parameter value will be identical to that obtained by evaluating the expression fn:abs#1 within the target XSLT stylesheet.

      This rule also applies when the target function definition is nondeterministicFO. For example all evaluations of the named function reference map:keys#2 return identical function items, even though two evaluations of map:keys with the same arguments may produce different results.

  • arity: As specified in the named function reference.

  • parameter names: The first A parameter names of FD, where A is the required arity.

  • signature: Formed from the required types of the first A parameters of FD, and the function result type of FD.

  • body: The body of FD.

  • captured context: Comprises the static and dynamic context of the named function reference, augmented with bindings of the names of parameters of FD beyond the A’th parameter, to their respective default values.

    Note:

    In practice, it is necessary to retain only the parts of the context that the function actually depends on (if any).

Note:

Consider the system function fn:format-date, which has an arity range of 2 to 5. The named function reference fn:format-date#3 returns a function item whose three parameters correspond to the first three parameters of fn:format-date; the remaining two arguments will take their default values. To obtain an arity-3 function that binds to arguments 1, 2, and 5 of fn:format-date, use the partial function application format-date(?, ?, place := ?).

The following are examples of named function references:

  • fn:abs#1 references the fn:abs function which takes a single argument.

  • fn:concat#5 references the fn:concat function which takes 5 arguments.

  • local:myfunc#2 references a function named local:myfunc which takes 2 arguments.

Note:

Function items, as values in the data model, have a fixed arity, and a dynamic function call always supplies the arguments positionally. In effect, the result of evaluating my:func#3 is the same as the result of evaluating the inline function expression fn($x, $y, $z) { my:func($x, $y, $z) }, except that the returned function has a name (it retains the name my:func).

4.5.2.5 Inline Function Expressions

Changes in 4.0  

  1. In inline function expressions, the keyword function may be abbreviated as fn.   [Issue 1192 PR 1197 21 May 2024]

  2. New abbreviated syntax is introduced (focus function) for simple inline functions taking a single argument. An example is fn { ../@code }  [Issue 503 PR 521 30 May 2023]

InlineFunctionExpr::=Annotation* ("function" | "fn") FunctionSignature? FunctionBody
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
AnnotationValue::=StringLiteral | ("-"? NumericLiteral) | ("true" "(" ")") | ("false" "(" ")")
FunctionSignature::="(" ParamList ")" TypeDeclaration?
ParamList::=(VarNameAndType ** ",")
VarNameAndType::="$" EQNameTypeDeclaration?
TypeDeclaration::="as" SequenceType

[Definition: An inline function expression, when evaluated, creates an anonymous function defined directly in the inline function expression.] An inline function expression specifies the names and SequenceTypes of the parameters to the function, the SequenceType of the result, and the body of the function.

An inline function expression whose FunctionSignature is omitted is known as a focus function. Focus functions are described in 4.5.2.6 Focus Functions.

[Definition: An anonymous function is a function item with no name. Anonymous functions may be created, for example, by evaluating an inline function expression or by partial function application.]

The keywords function and fn are synonymous.

The syntax allows the names and types of the function argument to be declared, along with the type of the result:

function($x as xs:integer, $y as xs:integer) as xs:integer { $x + $y }

The types can be omitted, and the keyword can be abbreviated:

fn($x, $y) { $x + $y }

A zero-arity function can be written as, for example, fn() { current-date() }.

If a function parameter is declared using a name but no type, its default type is item()*. If the result type is omitted, its default result type is item()*.

The parameters of an inline function expression are considered to be variables whose scope is the function body. It is a static error [err:XQST0039] for an inline function expression to have more than one parameter with the same name.

An inline function expression may have annotations. XQuery 4.0 does not define annotations that apply to inline function expressions, in particular it is a static error [err:XQST0125] if an inline function expression is annotated as %public or %private. An implementation can define annotations, in its own namespace, to support functionality beyond the scope of this specification.

The static context for the function body is inherited from the location of the inline function expression, with the exception of the static type of the context value which is initially absentDM.

The variables in scope for the function body include all variables representing the function parameters, as well as all variables that are in scope for the inline function expression.

Note:

Function parameter names can mask variables that would otherwise be in scope for the function body.

The result of an inline function expression is a single function item with the following properties (as defined in Section 2.9.4 Function ItemsDM):

  • name: Absent.

  • identity: A new function identity distinct from the identity of any other function item.

  • parameter names: The parameter names in the InlineFunctionExpr’s ParamList.

  • signature: A FunctionType constructed from the Annotations andSequenceTypes in the InlineFunctionExpr. An implementation which can determine a more specific signature (for example, through use of type analysis of the function’s body) is permitted to do so.

  • body: The InlineFunctionExpr’s FunctionBody.

  • captured context: the static context is the static context of the inline function expression, with the exception of the static context value type which is absentDM. The dynamic context has an absent focus, and a set of variable bindings comprising the variable values component of the dynamic context of the InlineFunctionExpr.

The following are examples of some inline function expressions:

  • This example creates a function that takes no arguments and returns a sequence of the first 6 primes:

    function() as xs:integer+ { 2, 3, 5, 7, 11, 13 }
  • This example creates a function that takes two xs:double arguments and returns their product:

    fn($a as xs:double, $b as xs:double) as xs:double { $a * $b }
  • This example creates and invokes a function that captures the value of a local variable in its scope:

    let $incrementors := (
      for $x in 1 to 10
      return function($y) as xs:integer { $x + $y }
    )
    return $incrementors[2](4)

    The result of this expression is 6

4.5.2.6 Focus Functions

[Definition: A focus function is an inline function expression in which the function signature is implicit: the function takes a single argument of type item()* (that is, any value), and binds this to the context value when evaluating the function body, which returns a result of type item()*.]

Here are some examples of focus functions:

  • fn { @age } - a function that expects a node as its argument, and returns the @age attribute of that node.

  • fn { . + 1 } - a function that expects a number as its argument, and returns that number plus one.

  • function { `${ . }` } - a function that expects a string as its argument, and prepends a "$" character.

  • function { head(.) + foot(.) } - a function that expects a sequence of numbers as its argument, and returns the sum of the first and last items in the sequence.

Focus functions are often useful as arguments to simple higher-order functions such as fn:sort. For example, to sort employees by salary, write sort(//employee, (), fn { +@salary }). (The unary plus has the effect of converting the attribute’s value to a number, for numeric sorting).

Focus functions can also be useful on the right-hand side of the sequence arrow operator and mapping arrow operator. For example, $s => tokenize() =!> fn { `"{.}"` }() first tokenizes the string $s, then wraps each token in double quotation marks.

The result of calling the function { EXPR } (or fn { EXPR }), with a single argument whose value is $Z arguments, is obtained by evaluating EXPR with a dynamic context in which the context value is $Z, the context position is 1 (one), and the context size is 1 (one).

For example, the expression every(1 to 10, fn { . gt 0 }) returns true.

4.5.2.7 Function Identity

It is sometimes useful to be able to establish whether two variables refer to the same function or to different functions. For this purpose, every function item has an identity. Functions with the same identity are indistinguishable in every way; in particular, any function call with identical arguments will produce an identical result.

In general, evaluation of an expression that returns a function item other than one that was present in its operands delivers a function item whose identity is unique, and thus distinct from any other function item. There are two exceptions to this rule:

  • Evaluating a function reference such as count#1 returns the same function every time. Specifically, if the function name identifies a function definition that is not context dependent (which is the most usual case), then all function references using this function name and arity return the same function. For more details see 4.5.2.4 Named Function References.

  • An optimizer is permitted to rewrite deterministicFO expressions in such a way that repeated evaluation is avoided, and this may be done without consideration of function identity. For example, if the expression contains(?, "e") appears within the body of a for clause, or if the same expression is written repeatedly in a query, then an optimizer may decide to evaluate it once only, and thus return the same function item each time. Similarly, if the expression fn($x) { $x + 1 } appears more than once, or is evaluated repeatedly, then it may return the same function each time.

  • In addition, optimizers are allowed to replace any expression with an equivalent expression. For example, count(?) may be rewritten as count#1. Similarly, fn($x) { $x + 1 } may be rewritten as fn($y) { $y + 1 }. This may lead to different expressions returning identical function items.

4.6 Path Expressions

PathExpr::=("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* xgc: leading-lone-slash */
RelativePathExpr::=StepExpr (("/" | "//") StepExpr)*

[Definition: A path expression consists of a series of one or more steps, separated by / or //, and optionally beginning with / or //. A path expression is typically used to locate nodes within trees. ]

Absolute path expressions (those starting with an initial / or //), start their selection from the root node of a tree; relative path expressions (those without a leading / or //) start from the context value.

A path expression consisting of a single step is evaluated as described in 4.6.4 Steps.

4.6.1 Absolute Path Expressions

A path expression consisting of / on its own is treated as an abbreviation for /..

An expression of the form /PP (that is, a path expression with a leading /) is treated as an abbreviation for the expression self::node()/(fn:root(.) treat as document-node())/PP. The effect of this expansion is that for every item J in the context value V:

  1. A type error occurs if J is not a node [err:XPTY0020].

  2. The root node R of the tree containing J is selected.

  3. A dynamic error occurs if R is not a document node [err:XPDY0050].

  4. The expression that follows the leading / is evaluated with R as the context value.

The results of these multiple evaluations are then combined into a single sequence; if the result is a set of nodes, the nodes are delivered in document order with duplicates eliminated.

Note:

The / character can be used either as a complete path expression or as the beginning of a longer path expression such as /*. Also, * is both the multiply operator and a wildcard in path expressions. This can cause parsing difficulties when / appears on the left-hand side of *. This is resolved using the leading-lone-slash constraint. For example, /* and / * are valid path expressions containing wildcards, but /*5 and / * 5 raise syntax errors. Parentheses must be used when / is used on the left-hand side of an operator that could be confused with a node test, as in (/) * 5. Similarly, 4 + / * 5 raises a syntax error, but 4 + (/) * 5 is a valid expression. The expression 4 + / is also valid, because / does not occur on the left-hand side of the operator.

Similarly, in the expression / union /*, union is interpreted as an element name rather than an operator. For it to be parsed as an operator, the expression should be written (/) union /*.

An expression of the form //PP (that is, a path expression with a leading //) is treated as an abbreviation for the expression self::node()/(fn:root(.) treat as document-node())/descendant-or-self:node()/PP. The effect of this expansion is that for every item J in the context value V:

  1. A type error occurs if J is not a node [err:XPTY0020].

  2. The root node R of the tree containing J is selected.

  3. A dynamic error occurs if R is not a document node [err:XPDY0050].

  4. The descendants of R are selected, along with R itself.

  5. For every node D in this set of nodes, the expression that follows the leading // is evaluated with D as the context value.

The results of these multiple evaluations are then combined into a single sequence; if the result is a set of nodes, the nodes are delivered in document order with duplicates eliminated.

If the context value is not a node, a type error is raised [err:XPTY0020]. At evaluation time, if the root node of the context node is not a document node, a dynamic error is raised [err:XPDY0050].

Note:

The descendants of a node do not include attribute nodes. However, the rules for expanding // ensure that .//@* selects all attributes of all descendants

Note:

// on its own is not a valid expression.

4.6.2 Relative Path Expressions

RelativePathExpr::=StepExpr (("/" | "//") StepExpr)*

A relative path expression is a path expression that selects nodes within a tree by following a series of steps starting at the nodes in the context value (which may be any kind of node, not necessarily the root of the tree).

Each non-initial occurrence of // in a path expression is expanded as described in 4.6.7 Abbreviated Syntax, leaving a sequence of steps separated by /. This sequence of steps is then evaluated from left to right. So a path such as E1/E2/E3/E4 is evaluated as ((E1/E2)/E3)/E4. The semantics of a path expression are thus defined by the semantics of the binary / operator, which is defined in 4.6.3 Path operator (/).

Note:

Although the semantics describe the evaluation of a path with more than two steps as proceeding from left to right, the / operator is in most cases associative, so evaluation from right to left usually delivers the same result. The cases where / is not associative arise when the functions fn:position() and fn:last() are used: A/B/position() delivers a sequence of integers from 1 to the size of (A/B), whereas A/(B/position()) restarts the counting at each B element.

The following example illustrates the use of relative path expressions. In each case it is assumed that the context value is a single node, referred to as the context node.

  • child::div1/child::para

    Selects the para element children of the div1 element children of the context node; that is, the para element grandchildren of the context node that have div1 parents.

Note:

Since each step in a path provides context nodes for the following step, in effect, only the last step in a path is allowed to return a sequence of non-nodes.

4.6.3 Path operator (/)

The path operator / is primarily used for locating nodes within trees. Its left-hand operand must return a sequence of nodes. The result of the operator is either a sequence of nodes (in document order, with no duplicates), or a sequence of non-nodes.

The operation E1/E2 is evaluated as follows: Expression E1 is evaluated, and if the result is not a (possibly empty) sequence S of nodes, a type error is raised [err:XPTY0019]. Each node in S then serves in turn to provide an inner focus (the node as the context value, its position in S as the context position, the length of S as the context size) for an evaluation of E2, as described in 2.2.2 Dynamic Context. The sequences resulting from all the evaluations of E2 are combined as follows:

  1. If every evaluation of E2 returns a (possibly empty) sequence of nodes, these sequences are combined, and duplicate nodes are eliminated based on node identity. The resulting node sequence is returned in document order.

  2. If every evaluation of E2 returns a (possibly empty) sequence of non-nodes, these sequences are concatenated, in order, and returned. The returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2.

  3. If the multiple evaluations of E2 return at least one node and at least one non-node, a type error is raised [err:XPTY0018].

Note:

The semantics of the path operator can also be defined using the simple map operator (!) as follows (the function fn:distinct-ordered-nodes($R) has the effect of eliminating duplicates and sorting nodes into document order):

let $R := E1 ! E2
return if (every $r in $R satisfies $r instance of node())
       then (fn:distinct-ordered-nodes($R))
       else if (every $r in $R satisfies not($r instance of node()))
       then $R
       else error()

For a table comparing the step operator to the map operator, see 4.22 Simple map operator (!).

4.6.4 Steps

StepExpr::=PostfixExpr | AxisStep
AxisStep::=(ReverseStep | ForwardStep) Predicate*
ForwardStep::=(ForwardAxisNodeTest) | AbbrevForwardStep
ReverseStep::=(ReverseAxisNodeTest) | AbbrevReverseStep
Predicate::="[" Expr "]"

[Definition: A step is a part of a path expression that generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates, working from left to right. A step may be either an axis step or a postfix expression.] Postfix expressions are described in 4.3 Postfix Expressions.

[Definition: An axis step returns a sequence of nodes that are reachable from a starting node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type annotation .]

If the context value is a sequence of zero or more nodes, an axis step returns a sequence of zero or more nodes; otherwise, a type error is raised [err:XPTY0020].

The step expression S is equivalent to ./S. Thus, if the context value is a sequence containing multiple nodes, the semantics of a step expression are equivalent to a path expression in which the step is always applied to a single node. The following description therefore explains the semantics for the case where the context value is a single node, called the context node.

Note:

The equivalence of a step S to the path expression ./S means that the resulting node sequence is returned in document order.

An axis step may be either a forward step or a reverse step, followed by zero or more predicates.

In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 4.6.7 Abbreviated Syntax.

The unabbreviated syntax for an axis step consists of the axis name and node test separated by a double colon. The result of the step consists of the nodes reachable from the starting node via the specified axis that have the node kind, name, and/or type annotation specified by the node test. For example, the step child::para selects the para element children of the context node: child is the name of the axis, and para is the name of the element nodes to be selected on this axis. The available axes are described in 4.6.4.1 Axes. The available node tests are described in 4.6.4.2 Node Tests. Examples of steps are provided in 4.6.6 Unabbreviated Syntax and 4.6.7 Abbreviated Syntax.

4.6.4.1 Axes

Changes in 4.0  

  1. Four new axes have been defined: preceding-or-self, preceding-sibling-or-self, following-or-self, and following-sibling-or-self.   [Issue 1519 ]

ForwardAxis::=("attribute"
| "child"
| "descendant"
| "descendant-or-self"
| "following"
| "following-or-self"
| "following-sibling"
| "following-sibling-or-self"
| "self") "::"
ReverseAxis::=("ancestor"
| "ancestor-or-self"
| "parent"
| "preceding"
| "preceding-or-self"
| "preceding-sibling-or-self") "::"

XQuery supports the following axes:

  • The child axis contains the children of the context node, which are the nodes returned by the Section 4.3 children AccessorDM.

    Note:

    Only document nodes and element nodes have children. If the context node is any other kind of node, or if the context node is an empty document or element node, then the child axis is an empty sequence. The children of a document node or element node may be element, processing instruction, comment, or text nodes. Attribute and document nodes can never appear as children.

  • The descendant axis is defined as the transitive closure of the child axis; it contains the descendants of the context node (the children, the children of the children, and so on).

    More formally, $node/descendant::node() delivers the result of fn:transitive-closure($node, fn { child::node() }).

  • The descendant-or-self axis contains the context node and the descendants of the context node.

    More formally, $node/descendant-or-self::node() delivers the result of $node/(. | descendant::node()).

  • The parent axis contains the sequence returned by the Section 4.11 parent AccessorDM, which returns the parent of the context node, or an empty sequence if the context node has no parent.

    Note:

    An attribute node may have an element node as its parent, even though the attribute node is not a child of the element node.

  • The ancestor axis is defined as the transitive closure of the parent axis; it contains the ancestors of the context node (the parent, the parent of the parent, and so on).

    More formally, $node/ancestor::node() delivers the result of fn:transitive-closure($node, fn { parent::node() }).

    Note:

    The ancestor axis includes the root node of the tree in which the context node is found, unless the context node is the root node.

  • The ancestor-or-self axis contains the context node and the ancestors of the context node; thus, the ancestor-or-self axis will always include the root node.

    More formally, $node/ancestor-or-self::node() delivers the result of $node/(. | ancestor::node()).

  • The following-sibling axis contains the context node’s following siblings, that is, those children of the context node’s parent that occur after the context node in document order. If the context node is an attribute or namespace node, the following-sibling axis is empty.

    More formally, $node/following-sibling::node() delivers the result of fn:siblings($node)[. >> $node]).

  • The following-sibling-or-self axis contains the context node, together with the contents of the following-sibling axis.

    More formally, $node/following-sibling-or-self::node() delivers the result of fn:siblings($node)[not(. << $node)]

  • The preceding-sibling axis contains the context node’s preceding siblings, that is, those children of the context node’s parent that occur before the context node in document order. If the context node is an attribute or namespace node, the preceding-sibling axis is empty.

    More formally, $node/preceding-sibling::node() delivers the result of fn:siblings($node)[. << $node].

  • The preceding-sibling-or-self axis contains the context node, together with the contents of the preceding-sibling axis.

    More formally, $node/preceding-sibling-or-self::node() delivers the result of fn:siblings($node)[not(. >> $node).

  • The following axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not descendants of the context node, and occur after the context node in document order.

    More formally, $node/following::node() delivers the result of $node/ancestor-or-self::node()/following-sibling::node()/descendant-or-self::node()

  • The following-or-self axis contains the context node, together with the contents of the following axis.

    More formally, $node/following-or-self::node() delivers the result of $node/(. | following::node()).

  • The preceding axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not ancestors of the context node, and occur before the context node in document order.

    More formally, $node/preceding::node() delivers the result of $node/ancestor-or-self::node()/preceding-sibling::node()/descendant-or-self::node().

  • The preceding-or-self axis contains the context node, together with the contents of the preceding axis.

    More formally, $node/preceding-or-self::node() delivers the result of $node/(. | preceding::node()).

  • The attribute axis contains the attributes of the context node, which are the nodes returned by the Section 4.1 attributes AccessorDM; the axis will be empty unless the context node is an element.

  • The self axis contains just the context node itself.

    The self axis is primarily useful when testing whether the context node satisfies particular conditions, for example if ($x[self::chapter]).

    More formally, $node/self::node() delivers the result of $node.

Axes can be categorized as forward axes and reverse axes. An axis that only ever contains the context node or nodes that are after the context node in document order is a forward axis. An axis that only ever contains the context node or nodes that are before the context node in document order is a reverse axis.

The parent, ancestor, ancestor-or-self, preceding, preceding-or-self, preceding-sibling, and preceding-sibling-or-self axes are reverse axes; all other axes are forward axes.

The ancestor, descendant, following, preceding and self axes partition a document (ignoring attribute nodes): they do not overlap and together they contain all the nodes in the document.

[Definition: Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.] Thus:

  • For the attribute axis, the principal node kind is attribute.

  • For all other axes, the principal node kind is element.

4.6.4.2 Node Tests

Changes in 4.0  

  1. If the default namespace for elements and types has the special value ##any, then an unprefixed name in a NameTest acts as a wildcard, matching names in any namespace or none.   [Issue 296 PR 1181 30 April 2024]

[Definition: A node test is a condition on the name, kind (element, attribute, text, document, comment, or processing instruction), and/or type annotation of a node. A node test determines which nodes contained by an axis are selected by a step.]

NodeTest::=UnionNodeTest | SimpleNodeTest
UnionNodeTest::="(" SimpleNodeTest ("|" SimpleNodeTest)* ")"
SimpleNodeTest::=KindTest | NameTest
NameTest::=EQName | Wildcard
Wildcard::="*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
EQName::=QName | URIQualifiedName
KindTest::=DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest

A UnionNodeTest matches a node N if at least one of the constituent SimpleNodeTests matches N.

For example, (div1|div2|div3) matches a node named div1, div2, or div3

[Definition: A node test that consists only of an EQName or a Wildcard is called a name test.] A name test that consists of an EQName matches a node N if and only if the kind of node N is the principal node kind for the step axis and the expanded QName of the node is equal (as defined by the eq operator) to the expanded QName specified by the name test. For example, child::para selects the para element children of the context node; if the context node has no para children, it selects an empty set of nodes. attribute::abc:href selects the attribute of the context node with the QName abc:href; if the context node has no such attribute, it selects an empty set of nodes.

If the EQName is a lexical QName, it is resolved into an expanded QName using the statically known namespaces in the expression context. It is a static error [err:XPST0081] if the QName has a prefix that does not correspond to any statically known namespace. An unprefixed QName, when used as a name test on an axis whose principal node kind is element, is interpreted as follows:

A name test is not satisfied by an element node whose name does not match the expanded QName of the name test, even if it is in a substitution group whose head is the named element.

A node test * is true for any node of the principal node kind of the step axis. For example, child::* will select all element children of the context node, and attribute::* will select all attributes of the context node.

A node test can have the form NCName:*. In this case, the prefix is expanded in the same way as with a lexical QName, using the statically known namespaces in the static context. If the prefix is not found in the statically known namespaces, a static error is raised [err:XPST0081]. The node test is true for any node of the principal node kind of the step axis whose expanded QName has the namespace URI to which the prefix is bound, regardless of the local part of the name.

A node test can contain a BracedURILiteral, for example Q{http://example.com/msg}*. Such a node test is true for any node of the principal node kind of the step axis whose expanded QName has the namespace URI specified in the BracedURILiteral, regardless of the local part of the name.

A node test can also have the form *:NCName. In this case, the node test is true for any node of the principal node kind of the step axis whose local name matches the given NCName, regardless of its namespace or lack of a namespace.

[Definition: An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.] The syntax and semantics of a kind test are described in 3.1 Sequence Types and 3.1.2 Sequence Type Matching. When a kind test is used in a node test, only those nodes on the designated axis that match the kind test are selected. Shown below are several examples of kind tests that might be used in path expressions:

  • node() matches any node.

  • text() matches any text node.

  • comment() matches any comment node.

  • namespace-node() matches any namespace node.

  • element() matches any element node.

  • schema-element(person) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation is the same as (or is derived from) the declared type of the person element in the in-scope element declarations.

  • element(person) matches any element node whose name is person, regardless of its type annotation.

  • element(doctor|nurse) matches any element node whose name is doctor or nurse, regardless of its type annotation.

  • element(person, surgeon) matches any non-nilled element node whose name is person, and whose type annotation is surgeon or is derived from surgeon.

  • element(doctor|nurse, medical-staff) matches any non-nilled element node whose name is doctor or nurse, and whose type annotation is medical-staff or is derived from medical-staff.

  • element(*, surgeon) matches any non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

  • attribute() matches any attribute node.

  • attribute(price) matches any attribute whose name is price, regardless of its type annotation.

  • attribute(*, xs:decimal) matches any attribute whose type annotation is xs:decimal (or is derived from xs:decimal), regardless of its name.

  • document-node() matches any document node.

  • document-node(element(book)) matches any document node whose children consist of a single element node that satisfies the kind testelement(book), interleaved with zero or more comments and processing instructions, and no text nodes.

  • document-node(book) is an abbreviation for document-node(element(book)).

4.6.4.3 Implausible Axis Steps

Changes in 4.0  

  1. The rules for reporting type errors during static analysis have been changed so that a processor has more freedom to report errors in respect of constructs that are evidently wrong, such as @price/@value, even though dynamic evaluation is defined to return an empty sequence rather than an error.   [Issue 602 PR 603 25 July 2023]

Certain axis steps, given an inferred type for the context value, are classified as implausible. During the static analysis phase, a processor may (subject to the rules in 2.4.6 Implausible Expressions) report a static error when such axis steps are encountered: [err:XPTY0144].

More specifically, an axis step is classified as implausible if any of the following conditions applies:

  1. The inferred item type of the context value is a node kind for which the specified axis is always empty: for example, the inferred item type of the context value is attribute() and the axis is child.

  2. The node test exclusively selects node kinds that cannot appear on the specified axis: for example, the axis is child and the node test is document-node().

  3. In a schema-aware environment, when using the child, descendant, descendant-or-self, or attribute axes, the inferred item type of the context value has a content type that does not allow any node matching the node test to be present on the relevant axis. For example, if the inferred item type of the context value is schema-element(list) and the relevant element declaration (taking into account substitution group membership and wildcards) only allows item children, the axis step child::li will never select anything and is therefore classified as implausible.

Examples of implausible axis steps include the following:

  • @code/text(): attributes cannot have text node children.

  • /@code: document nodes cannot have attributes.

  • ancestor::text(): the ancestor axis never returns text nodes.

Note:

Processors may choose not to classify the expression /.. as implausible, since XSLT 1.0 users were sometimes advised to use this construct as an explicit way of denoting the empty sequence.

4.6.5 Predicates within Steps

AxisStep::=(ReverseStep | ForwardStep) Predicate*
Predicate::="[" Expr "]"

A predicate within a AxisStep has similar syntax and semantics to a predicate within a filter expression. The only difference is in the way the context position is set for evaluation of the predicate.

Note:

The operator [] binds more tightly than /. This means that the expression a/b[1] is interpreted as child::a/(child::b[1]): it selects the first b child of every a element, in contrast to (a/b)[1] which selects the first b element that is a child of some a element.

A common mistake is to write //a[1] where (//a)[1] is intended. The first expression, //a[1], selects every descendant a element that is the first child of its parent (it expands to /descendant-or-self::node()/child::a[1]), whereas (//a)[1] selects the a element in the document.

For the purpose of evaluating the context position within a predicate, the input sequence is considered to be sorted as follows: into document order if the predicate is in a forward-axis step, into reverse document order if the predicate is in a reverse-axis step, or in its original order if the predicate is not in a step.

More formally:

  • For a step using a forwards axis, such as child::test[P], the result is the same as for the equivalent filter expression(child::test)[P] (note the parentheses). The same applies if there are multiple predicates, for example child::test[P1][P2][P3] is equivalent to (child::test)[P1][P2][P3].

  • For a step using a reverse axis, such as ancestor::test[P], the result is the same as the expression reverse(ancestor::test)[P] => reverse(). The same applies if there are multiple predicates, for example ancestor::test[P1][P2][P3] is equivalent to reverse(ancestor::test)[P1][P2][P3] => reverse().

Note:

The result of the expression preceding-sibling::* is in document order, but preceding-sibling::*[1] selects the last preceding sibling element, that is, the one that immediately precedes the context node.

Similarly, the expression preceding-sibling::x[1,2,3] selects the last three preceding siblings, returning them in document order. For example, given the input:

<doc><a/><b/><c/><d/><e/><f/></doc>

The result of //e ! preceding-sibling::*[1,2,3] is <b/>, <c/>, <d/>. The expression //e ! preceding-sibling::*[3,2,1] delivers exactly the same result.

Here are some examples of axis steps that contain predicates:

  • This example selects the second chapter element that is a child of the context node:

    child::chapter[2]
  • This example selects all the descendants of the context node that are elements named "toy" and whose color attribute has the value "red":

    descendant::toy[attribute::color = "red"]
  • This example selects all the employee children of the context node that have both a secretary child element and an assistant child element:

    child::employee[secretary][assistant]
  • This example selects the innermost div ancestor of the context node:

    ancestor::div[1]
  • This example selects the outermost div ancestor of the context node:

    ancestor::div[last()]
  • This example selects the names of all the ancestor elements of the context node that have an @id attribute, outermost element first:

    ancestor::*[@id]

Note:

The expression ancestor::div[1] parses as an AxisStep with a reverse axis, and the position 1 therefore refers to the first ancestor div in reverse document order, that is, the innermost div. By contrast, (ancestor::div)[1] parses as a FilterExpr, and therefore returns the first qualifying div element in the order of the ancestor::div expression, which is in document order.

The fact that a reverse-axis step assigns context positions in reverse document order for the purpose of evaluating predicates does not alter the fact that the final result of the step is always in document order.

The expression ancestor::(div1|div2)[1] does not have the same meaning as (ancestor::div1|ancestor::div2)[1]. In the first expression, the predicate [1] is within a step that uses a reverse axis, so nodes are counted in reverse document order. In the second expression, the predicate applies to the result of a union expression, so nodes are counted in document order.

When the context value for evaluation of a step includes multiple nodes, the step is evaluated separately for each of those nodes, and the results are combined without reordering. This means, for example, that if the context value contains three list nodes, and each of those nodes has multiple item children, then the step item[1] will deliver a sequence of three item elements, namely the first item from each list, retaining the order of the respective list elements.

4.6.6 Unabbreviated Syntax

This section provides a number of examples of path expressions in which the axis is explicitly specified in each step. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 4.6.7 Abbreviated Syntax.

These examples assume that the context value is a single node, referred to as the context node.

  • child::para selects the para element children of the context node.

  • child::(para|bullet) selects the para and bullet element children of the context node.

  • child::* selects all element children of the context node.

  • child::text() selects all text node children of the context node.

  • child::(text()|comment()) selects all text node and comment node children of the context node.

  • child::node() selects all the children of the context node. Note that no attribute nodes are returned, because attributes are not children.

  • attribute::name selects the name attribute of the context node.

  • attribute::* selects all the attributes of the context node.

  • parent::node() selects the parent of the context node. If the context node is an attribute node, this expression returns the element node (if any) to which the attribute node is attached.

  • descendant::para selects the para element descendants of the context node.

  • ancestor::div selects all div ancestors of the context node.

  • ancestor-or-self::div selects the div ancestors of the context node and, if the context node is a div element, the context node as well.

  • descendant-or-self::para selects the para element descendants of the context node and, if the context node is a para element, the context node as well.

  • self::para selects the context node if it is a para element, and otherwise returns an empty sequence.

  • self::(chapter|appendix) selects the context node if it is a chapter or appendix element, and otherwise returns an empty sequence.

  • child::chapter/descendant::para selects the para element descendants of the chapter element children of the context node.

  • child::*/child::para selects all para grandchildren of the context node.

  • / selects the root of the tree that contains the context node, but raises a dynamic error if this root is not a document node.

  • /descendant::para selects all the para elements in the same document as the context node.

  • /descendant::list/child::member selects all the member elements that have a list parent and that are in the same document as the context node.

  • child::para[position() = 1] selects the first para child of the context node.

  • child::para[position() = last()] selects the last para child of the context node.

  • child::para[position() = last()-1] selects the last but one para child of the context node.

  • child::para[position() > 1] selects all the para children of the context node other than the first para child of the context node.

  • following-sibling::chapter[position() = 1] selects the next chapter sibling of the context node.

  • following-sibling::(chapter|appendix)[position() = 1] selects the next sibling of the context node that is either a chapter or an appendix.

  • preceding-sibling::chapter[position() = 1] selects the previous chapter sibling of the context node.

  • /descendant::figure[position() = 42] selects the forty-second figure element in the document containing the context node.

  • /child::book/child::chapter[position() = 5]/child::section[position() = 2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node.

  • child::para[attribute::type eq "warning"] selects all para children of the context node that have a type attribute with value warning.

  • child::para[attribute::type eq 'warning'][position() = 5] selects the fifth para child of the context node that has a type attribute with value warning.

  • child::para[position() = 5][attribute::type eq "warning"] selects the fifth para child of the context node if that child has a type attribute with value warning.

  • child::chapter[child::title = 'Introduction'] selects the chapter children of the context node that have one or more title children whose typed value is equal to the string Introduction.

  • child::chapter[child::title] selects the chapter children of the context node that have one or more title children.

  • child::*[self::chapter or self::appendix] selects the chapter and appendix children of the context node.

  • child::*[self::(chapter|appendix)][position() = last()] selects the last chapter or appendix child of the context node.

4.6.7 Abbreviated Syntax

AbbrevForwardStep::=("@" NodeTest) | SimpleNodeTest
AbbrevReverseStep::=".."

The abbreviated syntax permits the following abbreviations:

  1. The attribute axis attribute:: can be abbreviated by @. For example, a path expression para[@type = "warning"] is short for child::para[attribute::type = "warning"] and so selects para children with a type attribute with value equal to warning.

  2. If the axis name is omitted from an axis step, the default axis is child, with two exceptions: (1) if the NodeTest in an axis step contains an AttributeTest or SchemaAttributeTest then the default axis is attribute; (2) if the NodeTest in an axis step is a NamespaceNodeTestthen a static error is raised [err:XQST0134].

    Note:

    The namespace axis is deprecated as of XPath 2.0, but is required in some languages that use XPath, including XSLT.

    For example, the path expression section/para is an abbreviation for child::section/child::para, and the path expression section/@id is an abbreviation for child::section/attribute::id. Similarly, section/attribute(id) is an abbreviation for child::section/attribute::attribute(id). Note that the latter expression contains both an axis specification and a node test.

    Note:

    An abbreviated axis step that omits the axis name must use a SimpleNodeTest rather than a UnionNodeTest. This means that a construct such as (ul|ol) is treated as an abbreviation for (child::ul|child::ol) rather than child::(ul|ol). Since the two constructs have exactly the same semantics, this is not actually a restriction.

  3. Each non-initial occurrence of // is effectively replaced by /descendant-or-self::node()/ during processing of a path expression. For example, div1//para is short for child::div1/descendant-or-self::node()/child::para and so will select all para descendants of div1 children.

    Note:

    The path expression //para[1] does not mean the same as the path expression /descendant::para[1]. The latter selects the first descendant para element; the former selects all descendant para elements that are the first para children of their respective parents.

  4. A step consisting of .. is short for parent::node(). For example, ../title is short for parent::node()/child::title and so will select the title children of the parent of the context node.

    Note:

    The expression ., known as a context value reference, is a primary expression, and is described in 4.2.3 Context Value References.

Here are some examples of path expressions that use the abbreviated syntax. These examples assume that the context value is a single node, referred to as the context node:

  • para selects the para element children of the context node.

  • * selects all element children of the context node.

  • text() selects all text node children of the context node.

  • @name selects the name attribute of the context node.

  • @(id|name) selects the id and name attributes of the context node.

  • @* selects all the attributes of the context node.

  • para[1] selects the first para child of the context node.

  • para[last()] selects the last para child of the context node.

  • */para selects all para grandchildren of the context node.

  • /book/chapter[5]/section[2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node.

  • chapter//para selects the para element descendants of the chapter element children of the context node.

  • //para selects all the para descendants of the root document node and thus selects all para elements in the same document as the context node.

  • //@version selects all the version attribute nodes that are in the same document as the context node.

  • //list/member selects all the member elements in the same document as the context node that have a list parent.

  • .//para selects the para element descendants of the context node.

  • .. selects the parent of the context node.

  • ../@lang selects the lang attribute of the parent of the context node.

  • para[@type = "warning"] selects all para children of the context node that have a type attribute with value warning.

  • para[@type = "warning"][5] selects the fifth para child of the context node that has a type attribute with value warning.

  • para[5][@type = "warning"] selects the fifth para child of the context node if that child has a type attribute with value warning.

  • chapter[title = "Introduction"] selects the chapter children of the context node that have one or more title children whose typed value is equal to the string Introduction.

  • chapter[title] selects the chapter children of the context node that have one or more title children.

  • employee[@secretary and @assistant] selects all the employee children of the context node that have both a secretary attribute and an assistant attribute.

  • book/(chapter|appendix)/section selects every section element that has a parent that is either a chapter or an appendix element, that in turn is a child of a book element that is a child of the context node.

  • If E is any expression that returns a sequence of nodes, then the expression E/. returns the same nodes in document order, with duplicates eliminated based on node identity.

4.7 Sequence Expressions

XQuery 4.0 supports operators to construct, filter, and combine sequences of items. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).

4.7.1 Sequence Concatenation

Expr::=(ExprSingle ++ ",")

[Definition: One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.] Empty parentheses can be used to denote an empty sequence.

A sequence may contain duplicate items, but a sequence is never an item in another sequence. When a new sequence is created by concatenating two or more input sequences, the new sequence contains all the items of the input sequences and its length is the sum of the lengths of the input sequences.

[Definition: The sequence concatenation of a number of sequences S1, S2, ... Sn is defined to be the sequence formed from the items of S1, followed by the items from S2, and so on, retaining order.] The comma operator returns the sequence concatenation of its two operands; repeated application (for example $s1, $s2, $s3, $s4) delivers the sequence concatenation of multiple sequences.

Note:

In places where the grammar calls for ExprSingle, such as the arguments of a function call, any expression that contains a top-level comma operator must be enclosed in parentheses.

Here are some examples of expressions that construct sequences:

  • The result of this expression is a sequence of five integers:

    (10, 1, 2, 3, 4)
  • This expression combines four sequences of length one, two, zero, and two, respectively, into a single sequence of length five. The result of this expression is the sequence 10, 1, 2, 3, 4.

    (10, (1, 2), (), (3, 4))
  • The result of this expression is a sequence containing all salary children of the context node followed by all bonus children.

    (salary, bonus)
  • Assuming that $price is bound to the value 10.50, the result of this expression is the sequence 10.50, 10.50.

    ($price, $price)

4.7.2 Range Expressions

RangeExpr::=AdditiveExpr ( "to" AdditiveExpr )?

A RangeExpression can be used to construct a sequence of integers. Each of the operands is converted as though it was an argument of a function with the expected parameter type xs:integer?. If either operand is an empty sequence, or if the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence. If the two operands convert to the same integer, the result of the range expression is that integer. Otherwise, the result is a sequence containing the two integer operands and every integer between the two operands, in increasing order.

The following examples illustrate the semantics:

  • 1 to 4 returns the sequence 1, 2, 3, 4

  • 10 to 10 returns the singleton sequence 10

  • 10 to 1 returns the empty sequence

  • -13 to -10 returns the sequence -13, -12, -11, -10

More formally, a RangeExpression is evaluated as follows:

  1. Each of the operands of the to operator is converted as though it was an argument of a function with the expected parameter type xs:integer?.

  2. If either operand is an empty sequence, or if the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence.

  3. If the two operands convert to the same integer, the result of the range expression is that integer.

  4. Otherwise, the result is a sequence containing the two integer operands and every integer between the two operands, in increasing order.

The following examples illustrate the use of RangeExpressions .

This example uses a range expression as one operand in constructing a sequence. It evaluates to the sequence 10, 1, 2, 3, 4.

(10, 1 to 4)

This example selects the first four items from an input sequence:

$input[position() = 1 to 4]

This example returns the sequence (0, 0.1, 0.2, 0.3, 0.5):

$x = (1 to 5)!.*0.1

This example constructs a sequence of length one containing the single integer 10.

10 to 10

The result of this example is a sequence of length zero.

15 to 10

This example uses the fn:reverse function to construct a sequence of six integers in decreasing order. It evaluates to the sequence 15, 14, 13, 12, 11, 10.

reverse(10 to 15)

Note:

To construct a sequence of integers based on steps other than 1, use the fn:slice function, as defined in Section 14.1 General functions and operators on sequences FO31.

4.7.3 Combining Node Sequences

UnionExpr::=IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
IntersectExceptExpr::=InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*

XQuery 4.0 provides the following operators for combining sequences of nodes:

  • The union and | operators are equivalent. They take two node sequences as operands and return a sequence containing all the nodes that occur in either of the operands.

  • The intersect operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in both operands.

  • The except operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in the first operand but not in the second operand.

All these operators eliminate duplicate nodes from their result sequences based on node identity. The resulting sequence is returned in document order.

If an operand of union, intersect, or except contains an item that is not a node, a type error is raised [err:XPTY0004].

If an IntersectExceptExpr contains more than two InstanceofExprs, they are grouped from left to right. With a UnionExpr, it makes no difference how operands are grouped, the results are the same.

Here are some examples of expressions that combine sequences. Assume the existence of three element nodes that we will refer to by symbolic names A, B, and C. Assume that the variables $seq1, $seq2 and $seq3 are bound to the following sequences of these nodes:

  • $seq1 is bound to (A, B)

  • $seq2 is bound to (A, B)

  • $seq3 is bound to (B, C)

Then:

  • $seq1 union $seq2 evaluates to the sequence (A, B).

  • $seq2 union $seq3 evaluates to the sequence (A, B, C).

  • $seq1 intersect $seq2 evaluates to the sequence (A, B).

  • $seq2 intersect $seq3 evaluates to the sequence containing B only.

  • $seq1 except $seq2 evaluates to the empty sequence.

  • $seq2 except $seq3 evaluates to the sequence containing A only.

In addition to the sequence operators described here, see Section 13 Functions and operators on sequencesFO for functions defined on sequences.

4.8 Arithmetic Expressions

Changes in 4.0  

  1. The symbols × and ÷ can be used for multiplication and division.

XQuery 4.0 provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.

AdditiveExpr::=MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
MultiplicativeExpr::=UnionExpr ( ("*" | "×" | "div" | "÷" | "idiv" | "mod") UnionExpr )*
UnaryExpr::=("-" | "+")* ValueExpr
ValueExpr::=ValidateExpr | ExtensionExpr | SimpleMapExpr

A subtraction operator must be preceded by whitespace if it could otherwise be interpreted as part of the previous token. For example, a-b will be interpreted as a name, but a - b and a -b will be interpreted as arithmetic expressions. (See A.3.5 Whitespace Rules for further details on whitespace handling.)

The arithmetic operator symbols * and × (xD7) are interchangeable, and denote multiplication.

The arithmetic operator symbols div and ÷ (xF7) are interchangeable, and denote division.

If an AdditiveExpr contains more than two MultiplicativeExprs, they are grouped from left to right. So, for instance,

A - B + C - D

is equivalent to

((A - B) + C) - D

Similarly, the operands of a MultiplicativeExpr are grouped from left to right.

The first step in evaluating an arithmetic expression is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent.

Each operand is evaluated by applying the following steps, in order:

  1. Atomization is applied to the operand. The result of this operation is called the atomized operand.

  2. If the atomized operand is an empty sequence, the result of the arithmetic expression is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. If the atomized operand is a sequence of length greater than one, a type error is raised [err:XPTY0004].

  4. If the atomized operand is of type xs:untypedAtomic, it is cast to xs:double. If the cast fails, a dynamic error is raised. [err:FORG0001]FO40

After evaluation of the operands, if the types of the operands are a valid combination for the given arithmetic operator, the operator is applied to the operands, resulting in an atomic item or a dynamic error (for example, an error might result from dividing by zero). The combinations of atomic types that are accepted by the various arithmetic operators, and their respective result types, are listed in B.2 Operator Mapping together with the operator functions that define the semantics of the operator for each type combination, including the dynamic errors that can be raised by the operator. The definitions of the operator functions are found in [XQuery and XPath Functions and Operators 4.0].

If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised [err:XPTY0004].

XQuery 4.0 provides three division operators:

Here are some examples of arithmetic expressions:

  • The first expression below returns the xs:decimal value -1.5, and the second expression returns the xs:integer value -1:

    -3 div 2
    -3 idiv 2
  • Subtraction of two date values results in a value of type xs:dayTimeDuration:

    $emp/hiredate - $emp/birthdate
  • This example illustrates the difference between a subtraction operator and a hyphen:

    $unit-price - $unit-discount
  • Unary operators have higher precedence than binary operators (other than !, /, and []), subject of course to the use of parentheses. Therefore, the following two examples have different meanings:

    -$bellcost + $whistlecost
    -($bellcost + $whistlecost)

Note:

Multiple consecutive unary arithmetic operators are permitted.

4.9 String Expressions

This section describes several ways of constructing strings.

4.9.1 String Concatenation Expressions

StringConcatExpr::=RangeExpr ( "||" RangeExpr )*

String concatenation expressions allow the string representations of values to be concatenated. In XQuery 4.0, $a || $b is equivalent to fn:concat($a, $b). The following expression evaluates to the string concatenate:

() || "con" || ("cat", "enate")

4.9.2 String Templates

Changes in 4.0  

  1. String templates provide a new way of constructing strings: for example `{$greeting}, {$planet}!` is equivalent to $greeting || ', ' || $planet || '!'  [Issue 58 PR 324 29 January 2023]

StringTemplate::="`" (StringTemplateFixedPart | StringTemplateVariablePart)* "`"
/* ws: explicit */
StringTemplateFixedPart::=((Char - ('{' | '}' | '`')) | "{{" | "}}" | "``")*
/* ws: explicit */
StringTemplateVariablePart::=EnclosedExpr
/* ws: explicit */
EnclosedExpr::="{" Expr? "}"

String templates provide an alternative way of constructing strings. For example, the expression `Pi is { round(math:pi(), 4) }` returns the string "Pi is 3.1416".

A string template starts and ends with U+0060 (GRAVE ACCENT, BACKTICK, `) , popularly known as a back-tick. Between the back-ticks is a string consisting of an sequence of fixed parts and variable parts:

  • A variable part consists of an optional XPath expression enclosed in curly brackets ({}): more specifically, a string conforming to the XPath production Expr?.

    Note:

    An expression within a variable part may contain an unescaped U+007B (LEFT CURLY BRACKET, {) or U+007D (RIGHT CURLY BRACKET, }) within a StringLiteral or within a comment.

    The fact that the expression is optional means that the string contained between the curly brackets may be zero-length, may comprise whitespace only, or may contain XPath comments. The effective value in this case is a zero-length string, which is equivalent to omitting the variable part entirely, together with its curly-bracket delimiters.

  • A fixed part may contain any characters, except that:

    • The character U+007B (LEFT CURLY BRACKET, {) must be written as {{.

    • The character U+007D (RIGHT CURLY BRACKET, }) must be written as }}.

    • The character U+0060 (GRAVE ACCENT, BACKTICK, `) must be written as ``.

    Following the principles of the “longest token” rule, any occurrence of {{ within the fixed part is interpreted as an escaped left curly bracket. This means that the enclosed expression must not start with U+007B (LEFT CURLY BRACKET, {) : if this is required, the two left curly brackets can be separated by whitespace. For example the string template `{{"key":"{ {1:"yes", 0:"no"}?$condition}"}}` evaluates to the string {"key":"yes"} or {"key":"no"} depending on the value of $condition.

    By contrast, if the enclosed expression ends with U+007D (RIGHT CURLY BRACKET, }) , this can be immediately followed by the closing U+007D (RIGHT CURLY BRACKET, }) delimiter without intervening whitespace.

The result of evaluating a string template is the string obtained by concatenating the expansions of the fixed and variable parts:

  • The expansion of a fixed part is obtained by replacing any double curly brackets ({{ or }}) by the corresponding single curly bracket, and replacing doubled back-ticks (``) by a single back-tick.

  • The expansion of a variable part containing an expression is as follows:

    1. Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic items.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string.

    3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.

  • The expansion of an empty variable part (one that contains no expression) is a zero-length string.

For example:

let $greeting := "Hello",
    $planet := "Mars"
return `{ $greeting }, { $planet }!`

returns "Hello, Mars!".

The expression:

let $longMonths := (1, 3, 5, 7, 8, 10, 12)
return `The months with 31 days are: { $longMonths }.`

returns "The months with 31 days are: 1 3 5 7 8 10 12.".

Note:

The rules for processing an enclosed expression are identical to the rules for attributes in XQuery direct element constructors. These rules differ slightly from the rules in XSLT attribute value templates, where adjacent text nodes are concatenated with no separator, prior to atomization.

Note:

A string template containing no variable parts is effectively just another way of writing a string literal: "Goethe", 'Goethe', and `Goethe` are interchangeable. This means that back-ticks can sometimes be a useful way of delimiting a string that contains both single and double quotes: `He said: "I didn't."`.

It is sometimes useful to use string templates in conjunction with the fn:char function to build strings containing special characters, for example `Chapter{ fn:char("nbsp") }{ $chapNr }`.

Note:

String literals containing an ampersand behave differently between XPath and XQuery: in XPath (unless first expanded by an XML parser) the string literal "Bacon & Eggs" represents a string containing an ampersand, while in XQuery it is an error, because an ampersand is taken as introducing a character reference. This difference does not arise for string templates, since neither XPath nor XQuery recognizes entity or character references in a string template. This means that back-tick delimited strings (such as `Bacon & Eggs`) may be useful in contexts where an XPath expression is required to have the same effect whether it is evaluated using an XPath or an XQuery processor.

In XQuery, the token ``[ is recognized as the start of a string constructor, under the “longest token” rule (see A.3 Lexical structure). This means that the construct ``[1] is not recognized as a StringTemplate followed by a predicate. In the unlikely event that an empty StringTemplate followed by a predicate is wanted, whitespace or parentheses can be used to avoid the tokenization problem.

4.9.3 String Constructors

[Definition: A String Constructor creates a string from literal text and interpolated expressions. ]

The syntax of a string constructor is convenient for generating JSON, JavaScript, CSS, SPARQL, XQuery, XPath, or other languages that use curly brackets, quotation marks, or other strings that are delimiters in XQuery 4.0.

StringConstructor::="``[" StringConstructorContent "]``"
/* ws: explicit */
StringConstructorContent::=StringConstructorChars (StringInterpolationStringConstructorChars)*
/* ws: explicit */
StringConstructorChars::=(Char* - (Char* ('`{' | ']``') Char*))
/* ws: explicit */
StringInterpolation::="`{" Expr? "}`"
/* ws: explicit */

Note:

String templates (see 4.9.2 String Templates) and string constructors have overlapping functionality. String constructors were introduced in XQuery 3.1, and are not available in XPath; string templates are new in XQuery 4.0 and XPath 4.0. String constructors were designed specifically for convenience when generating code in languages that use curly brackets, but with experience, they have been found to be somewhat unwieldy for simpler applications; this motivated the introduction of a simpler syntax in 4.0.

In a string constructor, adjacent string constructor characters are treated as literal text. Line endings are processed as elsewhere in XQuery; no other processing is performed on this text. To evaluate a string constructor, each sequence of adjacent string constructor characters is converted to a string containing the same characters, and each string constructor interpolation$i is evaluated, then converted to a string using the expression string-join($i, ' '). A string constructor interpolation that does not contain an expression (`{ }`) is ignored. The strings created from string constructor characters and the strings created from string constructor interpolations are then concatenated, in order.

For instance, the following expression:

for $s in ("one", "two", "red", "blue")
return ``[`{ $s }` fish]``

evaluates to the sequence ("one fish", "two fish", "red fish", "blue fish").

Note:

Character entities are not expanded in string constructor content. Thus, ``[&lt;]`` evaluates to the string "&lt;", not the string "<".

Interpolations can contain string constructors. For instance, consider the following expression:

``[`{ $i, ``[literal text]``, $j, ``[more literal text]`` }`]``

Assuming the values $i := 1 and $j := 2, this evaluates to the string "1 literal text 2 more literal text".

The following examples are based on an example taken from the documentation of [Moustache], a JavaScript template library. Each function takes a map, containing values like these:

{
  "name": "Chris",
  "value": 10000,
  "taxed_value": 10000 - (10000 * 0.4),
  "in_ca": true
}

This function creates a simple string.

declare function local:prize-message($a) as xs:string {
  ``[Hello `{ $a?name }`
You have just won `{ $a?value }` dollars!
`{ 
   if ($a?in_ca) 
   then ``[Well, `{ $a?taxed_value }` dollars, after taxes.]``
   else ""
}`]``
};

This is the output of the above function :

Hello Chris
You have just won 10000 dollars!
Well, 6000 dollars, after taxes.

This function creates a similar string in HTML syntax.

declare function local:prize-message($a) as xs:string {
  ``[<div>
  <h1>Hello `{ $a?name }`</h1>
  <p>You have just won `{ $a?value }` dollars!</p>
    `{ 
      if ($a?in_ca) 
      then ``[  <p>Well, `{ $a?taxed_value }` dollars, after taxes.</p> ]``
      else ""
    }`
</div>]``
};

This is the output of the above function :

<div>
  <h1>Hello Chris</h1>
  <p>You have just won 10000 dollars!</p>
  <p>Well, 6000 dollars, after taxes.</p> 
</div>

This function creates a similar string in JSON syntax.

declare function local:prize-message($a) as xs:string {
  ``[{ 
  "name": `{ $a?name }`
  "value": `{ $a?value }`
  `{
  if ($a?in_ca) 
  then 
  ``[, 
  "taxed_value": `{ $a?taxed_value }`]``  
  else ""
  }`
}]`` 
};

This is the output of the above function :

{ 
  "name": "Chris",
  "value": 10000,
  "taxed_value": 6000
}

Within an enclosed expression, the handling of expressions that start with U+007B (LEFT CURLY BRACKET, {) or that end with U+007D (RIGHT CURLY BRACKET, }) is the same as for 4.9.2 String Templates.

4.10 Comparison Expressions

Comparison expressions allow two values to be compared. XQuery 4.0 provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.

ComparisonExpr::=OtherwiseExpr ( (ValueComp
| GeneralComp
| NodeComp) OtherwiseExpr )?
ValueComp::="eq" | "ne" | "lt" | "le" | "gt" | "ge"
GeneralComp::="=" | "!=" | "<" | "<=" | ">" | ">="
NodeComp::="is" | "<<" | ">>"

For a summary of the differences between different ways of comparing atomic items in XQuery 4.0, see I Atomic Comparisons: An Overview.

4.10.1 Value Comparisons

Changes in 4.0  

  1. The rules for value comparisons when comparing values of different types (for example, decimal and double) have changed to be transitive. A decimal value is no longer converted to double, instead the double is converted to a decimal without loss of precision. This may affect compatibility in edge cases involving comparison of values that are numerically very close.

The value comparison operators are eq, ne, lt, le, gt, and ge. Value comparisons are used for comparing single values.

The first step in evaluating a value comparison is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent. Each operand is evaluated by applying the following steps, in order:

  1. Atomization is applied to each operand. The result of this operation is called the atomized operand.

  2. If an atomized operand is an empty sequence, the result of the value comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. If an atomized operand is a sequence of length greater than one, a type error is raised [err:XPTY0004].

  4. If an atomized operand is of type xs:untypedAtomic, it is cast to xs:string.

    Note:

    The purpose of this rule is to make value comparisons transitive. Users should be aware that the general comparison operators have a different rule for casting of xs:untypedAtomic operands. Users should also be aware that transitivity of value comparisons may be compromised by loss of precision during type conversion (for example, two xs:integer values that differ slightly may both be considered equal to the same xs:float value because xs:float has less precision than xs:integer).

  5. If the two operands are instances of different primitive types (meaning the 19 primitive types defined in Section 3.2 Primitive datatypesXS2), then:

    1. If each operand is an instance of one of the types xs:string or xs:anyURI, then both operands are cast to type xs:string.

    2. If each operand is an instance of one of the types xs:decimal or xs:float, then both operands are cast to type xs:float.

    3. If each operand is an instance of one of the types xs:decimal, xs:float, or xs:double, then both operands are cast to type xs:double.

    4. Otherwise, a type error is raised [err:XPTY0004].

      Note:

      The primitive type of an xs:integer value for this purpose is xs:decimal.

  6. Finally, if the types of the operands are a valid combination for the given operator, the operator is applied to the operands.

The combinations of atomic types that are accepted by the various value comparison operators, and their respective result types, are listed in B.2 Operator Mapping together with the operator functions that define the semantics of the operator for each type combination. The definitions of the operator functions are found in [XQuery and XPath Functions and Operators 4.0].

Informally, if both atomized operands consist of exactly one atomic item, then the result of the comparison is true if the value of the first operand is (equal, not equal, less than, less than or equal, greater than, greater than or equal) to the value of the second operand; otherwise the result of the comparison is false.

If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised [err:XPTY0004].

Here are some examples of value comparisons:

  • The following comparison atomizes the node(s) that are returned by the expression $book/author. The comparison is true only if the result of atomization is the value "Kennedy" as an instance of xs:string or xs:untypedAtomic. If the result of atomization is an empty sequence, the result of the comparison is an empty sequence. If the result of atomization is a sequence containing more than one value, a type error is raised [err:XPTY0004].

    $book1/author eq "Kennedy"
  • The following comparison is true because atomization converts an array to its member sequence:

    [ "Kennedy" ] eq "Kennedy"
  • The following path expression contains a predicate that selects products whose weight is greater than 100. For any product that does not have a weight subelement, the value of the predicate is the empty sequence, and the product is not selected. This example assumes that weight is a validated element with a numeric type.

    //product[weight gt 100]
  • The following comparisons are true because, in each case, the two constructed nodes have the same value after atomization, even though they have different identities and/or names:

    <a>5</a> eq <a>5</a>
    <a>5</a> eq <b>5</b>
  • The following comparison is true if my:hatsize and my:shoesize are both user-defined types that are derived by restriction from a primitive numeric type:

    my:hatsize(5) eq my:shoesize(5)
  • The following comparison is true. The eq operator compares two QNames by performing codepoint-comparisons of their namespace URIs and their local names, ignoring their namespace prefixes.

    QName("http://example.com/ns1", "this:color") eq
    QName("http://example.com/ns1", "that:color")

4.10.2 General Comparisons

Changes in 4.0  

  1. Operators such as < and > can use the full-width forms and to avoid the need for XML escaping.

The general comparison operators are =, !=, <, <=, >, and >=. General comparisons are existentially quantified comparisons that may be applied to operand sequences of any length. The result of a general comparison that does not raise an error is always true or false.

A general comparison is evaluated by applying the following rules, in order:

  1. Atomization is applied to each operand. After atomization, each operand is a sequence of atomic items.

  2. The result of the comparison is true if and only if there is a pair of atomic items, one in the first operand sequence and the other in the second operand sequence, that have the required magnitude relationship. Otherwise the result of the comparison is false or an error. The magnitude relationship between two atomic items is determined by applying the following rules. If a cast operation called for by these rules is not successful, a dynamic error is raised. [err:FORG0001]FO40

    Note:

    The purpose of these rules is to preserve compatibility with XPath 1.0, in which (for example) x < 17 is a numeric comparison if x is an untyped value. Users should be aware that the value comparison operators have different rules for casting of xs:untypedAtomic operands.

    1. If both atomic items are instances of xs:untypedAtomic, then the values are cast to the type xs:string.

    2. If exactly one of the atomic items is an instance of xs:untypedAtomic, it is cast to a type depending on the other value’s dynamic type T according to the following rules, in which V denotes the value to be cast:

      1. If T is a numeric type or is derived from a numeric type, then V is cast to xs:double.

      2. If T is xs:dayTimeDuration or is derived from xs:dayTimeDuration, then V is cast to xs:dayTimeDuration.

      3. If T is xs:yearMonthDuration or is derived from xs:yearMonthDuration, then V is cast to xs:yearMonthDuration.

      4. In all other cases, V is cast to the primitive base type of T.

      Note:

      The special treatment of the duration types is required to avoid errors that may arise when comparing the primitive type xs:duration with any duration type.

    3. After performing the conversions described above, the atomic items are compared using one of the value comparison operators eq, ne, lt, le, gt, or ge, depending on whether the general comparison operator was =, !=, <, <=, >, or >=. The values have the required magnitude relationship if and only if the result of this value comparison is true.

When evaluating a general comparison in which either operand is a sequence of items, an implementation may return true as soon as it finds an item in the first operand and an item in the second operand that have the required magnitude relationship. Similarly, a general comparison may raise a dynamic error as soon as it encounters an error in evaluating either operand, or in comparing a pair of items from the two operands. As a result of these rules, the result of a general comparison is not deterministic in the presence of errors.

Here are some examples of general comparisons:

  • The following comparison is true if the typed value of any author subelement of $book1 is "Kennedy" as an instance of xs:string or xs:untypedAtomic:

    $book1/author = "Kennedy"
  • The following comparison is true because atomization converts an array to its member sequence:

    [ "Obama", "Nixon", "Kennedy" ] = "Kennedy"
  • The following example contains three general comparisons. The value of the first two comparisons is true, and the value of the third comparison is false. This example illustrates the fact that general comparisons are not transitive.

    (1, 2) = (2, 3)
    (2, 3) = (3, 4)
    (1, 2) = (3, 4)
  • The following example contains two general comparisons, both of which are true. This example illustrates the fact that the = and != operators are not inverses of each other.

    (1, 2) = (2, 3)
    (1, 2) != (2, 3)
  • Suppose that $a, $b, and $c are bound to element nodes with type annotation xs:untypedAtomic, with string values"1", "2", and "2.0" respectively. Then ($a, $b) = ($c, 3.0) returns false, because $b and $c are compared as strings. However, ($a, $b) = ($c, 2.0) returns true, because $b and 2.0 are compared as numbers.

4.10.3 Node Comparisons

Node comparisons are used to compare two nodes, by their identity or by their document order. The result of a node comparison is defined by the following rules:

  1. The operands of a node comparison are evaluated in implementation-dependent order.

  2. If either operand is an empty sequence, the result of the comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. Each operand must be either a single node or an empty sequence; otherwise a type error is raised [err:XPTY0004].

  4. A comparison with the is operator is true if the two operand nodes are the same node; otherwise it is false. See [XQuery and XPath Data Model (XDM) 4.0] for the definition of node identity.

  5. A comparison with the << operator returns true if the left operand node precedes the right operand node in document order; otherwise it returns false.

  6. A comparison with the >> operator returns true if the left operand node follows the right operand node in document order; otherwise it returns false.

Here are some examples of node comparisons:

  • The following comparison is true only if the left and right sides each evaluate to exactly the same single node:

    /books/book[isbn = "1558604820"] is /books/book[call = "QA76.9 C3845"]
  • The following comparison is false because each constructed node has its own identity:

    <a>5</a> is <a>5</a>
  • The following comparison is true only if the node identified by the left side occurs before the node identified by the right side in document order:

    /transactions/purchase[parcel = "28-451"] << /transactions/sale[parcel = "33-870"]

4.11 Logical Expressions

A logical expression is either an and-expression or an or-expression. If a logical expression does not raise an error, its value is always one of the boolean values true or false.

OrExpr::=AndExpr ( "or" AndExpr )*
AndExpr::=ComparisonExpr ( "and" ComparisonExpr )*

The first step in evaluating a logical expression is to find the effective boolean value of each of its operands (see 2.5.4 Effective Boolean Value).

The value of an and-expression is determined by the effective boolean values (EBVs) of its operands, as shown in the following table:

AND:EBV2 = trueEBV2 = falseerror in EBV2
EBV1 = truetruefalseerror
EBV1 = falsefalsefalseeither false or error
error in EBV1erroreither false or errorerror

The value of an or-expression is determined by the effective boolean values (EBVs) of its operands, as shown in the following table:

OR:EBV2 = trueEBV2 = falseerror in EBV2
EBV1 = truetruetrueeither true or error
EBV1 = falsetruefalseerror
error in EBV1either true or errorerrorerror

The order in which the operands of a logical expression are evaluated is implementation-dependent. The tables above are defined in such a way that an or-expression can return true if the first expression evaluated is true, and it can raise an error if evaluation of the first expression raises an error. Similarly, an and-expression can return false if the first expression evaluated is false, and it can raise an error if evaluation of the first expression raises an error. As a result of these rules, a logical expression is not deterministic in the presence of errors, as illustrated in the examples below.

Here are some examples of logical expressions:

  • The following expressions return true:

    1 eq 1 and 2 eq 2
    1 eq 1 or 2 eq 3
  • The following expression may return either false or raise a dynamic error :

    1 eq 2 and 3 idiv 0 = 1
  • The following expression may return either true or raise a dynamic error :

    1 eq 1 or 3 idiv 0 = 1
  • The following expression must raise a dynamic error:

    1 eq 1 and 3 idiv 0 = 1

In addition to and- and or-expressions, XQuery 4.0 provides a function named fn:not that takes a general sequence as parameter and returns a boolean value. The fn:not function is defined in [XQuery and XPath Functions and Operators 4.0]. The fn:not function reduces its parameter to an effective boolean value. It then returns true if the effective boolean value of its parameter is false, and false if the effective boolean value of its parameter is true. If an error is encountered in finding the effective boolean value of its operand, fn:not raises the same error.

4.12 Node Constructors

XQuery provides node constructors that can create XML nodes within a query.

NodeConstructor::=DirectConstructor
| ComputedConstructor
DirectConstructor::=DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
DirElemConstructor::="<" QNameDirAttributeList ("/>" | (">" DirElemContent* "</" QNameS? ">"))
/* ws: explicit */
DirElemContent::=DirectConstructor
| CDataSection
| CommonContent
| ElementContentChar
ElementContentChar::=(Char - [{}<&])
CommonContent::=PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
CDataSection::="<![CDATA[" CDataSectionContents "]]>"
/* ws: explicit */
CDataSectionContents::=(Char* - (Char* ']]>' Char*))
/* ws: explicit */
DirAttributeList::=(S (QNameS? "=" S? DirAttributeValue)?)*
/* ws: explicit */
DirAttributeValue::=('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
QuotAttrValueContent::=QuotAttrContentChar
| CommonContent
AposAttrValueContent::=AposAttrContentChar
| CommonContent
QuotAttrContentChar::=(Char - ["{}<&])
AposAttrContentChar::=(Char - ['{}<&])
EscapeQuot::='""'
/* ws: explicit */
EscapeApos::="''"
/* ws: explicit */
EnclosedExpr::="{" Expr? "}"

Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation that can incorporate enclosed expressions, and computed constructors, which use a notation based on enclosed expressions.

The rest of this section contains a conceptual description of the semantics of various kinds of constructor expressions. An XQuery implementation is free to use any implementation technique that produces the same result as the processing steps described here.

4.12.1 Direct Element Constructors

An element constructor creates an element node. [Definition: A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.] Direct element constructors are based on standard XML notation. For example, the following expression is a direct element constructor that creates a book element containing an attribute and some nested elements:

<book isbn="isbn-0060229357">
  <title>Harold and the Purple Crayon</title>
  <author>
    <first>Crockett</first>
    <last>Johnson</last>
  </author>
</book>

If the element name in a direct element constructor has a namespace prefix, the namespace prefix is resolved to a namespace URI using the statically known namespaces. If the element name has no namespace prefix, the namespace binding for the zero-length prefix in the statically known namespaces is used; if there is no such binding, the element name will be in no namespace.

Note:

The statically known namespaces may be affected by namespace declaration attributes found inside the element constructor.

The namespace prefix of the element name is retained after expansion of the lexical QName, as described in [XQuery and XPath Data Model (XDM) 4.0]. The resulting expanded QName becomes the node-name property of the constructed element node.

In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix [err:XQST0118].

In a direct element constructor, curly brackets (U+007B (LEFT CURLY BRACKET, {) and U+007D (RIGHT CURLY BRACKET, }) ) delimit enclosed expressions, distinguishing them from literal text. Enclosed expressions are evaluated and replaced by their value, as illustrated by the following example:

<example>
  <p> Here is a query. </p>
  <eg> $b/title </eg>
  <p> Here is the result of the query. </p>
  <eg>{ $b/title }</eg>
</example>

The above query might generate the following result (whitespace has been added for readability to this result and other result examples in this document):

<example>
  <p> Here is a query. </p>
  <eg> $b/title </eg>
  <p> Here is the result of the query. </p>
  <eg><title>Harold and the Purple Crayon</title></eg>
</example>

Since XQuery uses U+007B (LEFT CURLY BRACKET, {) and U+007D (RIGHT CURLY BRACKET, }) to delimit enclosed expressions, some convention is needed to denote a curly bracket used as an ordinary character. For this purpose, a pair of identical curly bracket characters within the content of an element or attribute are interpreted by XQuery as a single curly bracket character (that is, the pair "{{" represents the character U+007B (LEFT CURLY BRACKET, {) and the pair "}}" represents the character U+007D (RIGHT CURLY BRACKET, }) .) Alternatively, the character references&#x7b; and &#x7d; can be used to denote curly bracket characters. A single U+007B (LEFT CURLY BRACKET, {) is interpreted as the beginning delimiter for an enclosed expression. A single U+007D (RIGHT CURLY BRACKET, }) without a matching left curly bracket is treated as a static error [err:XPST0003].

Within an enclosed expression, the handling of expressions that start with U+007B (LEFT CURLY BRACKET, {) or that end with U+007D (RIGHT CURLY BRACKET, }) is the same as for 4.9.2 String Templates.

The result of an element constructor is a new element node, with its own node identity. All the attribute and descendant nodes of the new element node are also new nodes with their own identities, even if they are copies of existing nodes.

4.12.1.1 Attributes

The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant lexical QName, and the value of the attribute is specified by a string of characters enclosed in single or double quotes. As in the main content of the element constructor, an attribute value may contain enclosed expressions, which are evaluated and replaced by their value during processing of the element constructor.

Each attribute in a direct element constructor creates a new attribute node, with its own node identity, whose parent is the constructed element node. However, note that namespace declaration attributes (see 4.12.1.2 Namespace Declaration Attributes) do not create attribute nodes.

If an attribute name has a namespace prefix, the prefix is resolved to a namespace URI using the statically known namespaces. If the attribute name has no namespace prefix, the attribute is in no namespace. Note that the statically known namespaces used in resolving an attribute name may be affected by namespace declaration attributes that are found inside the same element constructor. The namespace prefix of the attribute name is retained after expansion of the lexical QName, as described in [XQuery and XPath Data Model (XDM) 4.0]. The resulting expanded QName becomes the node-name property of the constructed attribute node.

If the attributes in a direct element constructor do not have distinct expanded QNames as their respective node-name properties, a static error is raised [err:XQST0040].

Conceptually, an attribute (other than a namespace declaration attribute) in a direct element constructor is processed by the following steps:

  1. Each consecutive sequence of literal characters in the attribute content is processed as a string literal containing those characters, with the following exceptions:

    1. Each occurrence of two consecutive { characters is replaced by a single { character.

    2. Each occurrence of two consecutive } characters is replaced by a single } character.

    3. Each occurrence of EscapeQuot is replaced by a single " character.

    4. Each occurrence of EscapeApos is replaced by a single ' character.

    Within an enclosed expression, the handling of expressions that start with U+007B (LEFT CURLY BRACKET, {) or that end with U+007D (RIGHT CURLY BRACKET, }) is the same as for 4.9.2 String Templates.

    Attribute value normalization is then applied to normalize whitespace and expand character references and predefined entity references. The rules for attribute value normalization are the rules from Section 3.3.3 of [XML 1.0] or Section 3.3.3 of [XML 1.1] (it is implementation-defined which version is used). The rules are applied as though the type of the attribute were CDATA (leading and trailing whitespace characters are not stripped.)

  2. Each enclosed expression is converted to a string as follows:

    1. Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic items.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string.

    3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.

  3. Adjacent strings resulting from the above steps are concatenated with no intervening blanks. The resulting string becomes the string-value property of the attribute node. The attribute node is given a type annotation of xs:untypedAtomic (this type annotation may change if the parent element is validated). The typed-value property of the attribute node is the same as its string-value, as an instance of xs:untypedAtomic.

  4. The parent property of the attribute node is set to the element node constructed by the direct element constructor that contains this attribute.

  5. If the attribute name is xml:id, then xml:id processing is performed as defined in [XML ID]. This ensures that the attribute has the type xs:ID and that its value is properly normalized. If an error is encountered during xml:id processing, an implementation may raise a dynamic error [err:XQDY0091].

  6. If the attribute name is xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.

  • Example:

    <shoe size="7"/>

    The string value of the size attribute is "7".

  • Example:

    <shoe size="{ 7 }"/>

    The string value of the size attribute is "7".

  • Example:

    <shoe size="{ () }"/>

    The string value of the size attribute is the zero-length string.

  • Example:

    <chapter ref="[{ 1, 5 to 7, 9 }]"/>

    The string value of the ref attribute is "[1 5 6 7 9]".

  • Example:

    <shoe size="As big as { $hat/@size }"/>

    The string value of the size attribute is the string "As big as ", concatenated with the string value of the node denoted by the expression $hat/@size.

4.12.1.2 Namespace Declaration Attributes

Changes in 4.0  

  1. The default namespace for elements and types can now be declared to be fixed for a query module, meaning it is unaffected by a namespace declaration appearing on a direct element constructor.   [Issue 65 PR 753 31 October 2023]

The names of a constructed element and its attributes may be lexical QNames that include namespace prefixes. Namespace prefixes can be bound to namespaces in the Prolog or by namespace declaration attributes. It is a static error to use a namespace prefix that has not been bound to a namespace [err:XPST0081].

[Definition: A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix (including the zero-length prefix) for the constructed element node, including its attributes.] Syntactically, a namespace declaration attribute has the form of an attribute with namespace prefix xmlns, or with name xmlns and no namespace prefix. All the namespace declaration attributes of a given element must have distinct names [err:XQST0071]. Each namespace declaration attribute is processed as follows:

  • The value of the namespace declaration attribute (a DirAttributeValue) is processed as follows. If the DirAttributeValue contains an EnclosedExpr, a static error is raised [err:XQST0022]. Otherwise, it is processed as described in rule 1 of 4.12.1.1 Attributes. An implementation may raise a static error[err:XQST0046] if the resulting value is of nonzero length and is neither an absolute URI nor a relative URI. The resulting value is used as the namespace URI in the following rules.

  • If the prefix of the attribute name is xmlns, then the local part of the attribute name is interpreted as a namespace prefix. This prefix and the namespace URI are added to the statically known namespaces of the constructor expression (overriding any existing binding of the given prefix), and are also added as a namespace binding to the in-scope namespaces of the constructed element. If the namespace URI is a zero-length string and the implementation supports [XML Names 1.1], any existing namespace binding for the given prefix is removed from the in-scope namespaces of the constructed element and from the statically known namespaces of the constructor expression. If the namespace URI is a zero-length string and the implementation does not support [XML Names 1.1], a static error is raised [err:XQST0085]. It is implementation-defined whether an implementation supports [XML Names] or [XML Names 1.1].

  • If the name of the namespace declaration attribute is xmlns with no prefix, then:

  • It is a static error [err:XQST0070] if a namespace declaration attribute attempts to do any of the following:

    • Bind the prefix xml to some namespace URI other than http://www.w3.org/XML/1998/namespace.

    • Bind a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.

    • Bind the prefix xmlns to any namespace URI.

    • Bind a prefix to the namespace URI http://www.w3.org/2000/xmlns/.

A namespace declaration attribute does not cause an attribute node to be created.

The following examples illustrate namespace declaration attributes:

  • In this element constructor, a namespace declaration attribute is used to set the default namespace to http://example.org/animals:

    <cat xmlns="http://example.org/animals">
      <breed>{ variety/@name }</breed>
    </cat>

    More specifically:

    • The expanded name of the constructed element will be Q{http://example.org/animals}cat.

    • The constructed element will have a namespace binding that associates the empty prefix with the namespace URI http://example.org/animals.

    • The static context for evaluation of any expressions within the element constructor will include a binding of the empty prefix to the namespace URI http://example.org/animals. This ensures that the nested breed element will also be in the namespace http://example.org/animals.

    • The default namespace for elements and types within the element constructor will be http://example.org/animals, which means that the element name variety is also interpreted as being in this namespace. This effect may be unwanted, since the document containing the context node may well use a different default namespace. In XQuery 4.0 this effect can be prevented by declaring, in the query prolog, that the default namespace for elements and types is fixed. Alternatively the path expression can be written Q{}variety/@name to make it explicit that variety refers to a no-namespace element.

  • In this element constructor, namespace declaration attributes are used to bind the namespace prefixes metric and english:

    <box xmlns:metric="http://example.org/metric/units"
         xmlns:english = "http://example.org/english/units">
      <height> <metric:meters>3</metric:meters> </height>
      <width> <english:feet>6</english:feet> </width>
      <depth> <english:inches>18</english:inches> </depth>
    </box>
4.12.1.3 Content

The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of text characters (parsed as ElementContentChar), nested direct constructors, CDataSections, character and predefined entity references, and enclosed expressions. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic items. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.

Conceptually, the content of an element constructor is processed as follows:

  1. The content is evaluated to produce a sequence of nodes called the content sequence, as follows:

    1. If the boundary-space policy in the static context is strip, boundary whitespace is identified and deleted (see 4.12.1.4 Boundary Whitespace for the definition of boundary whitespace.)

    2. Predefined entity references and character references are expanded into their referenced strings, as described in 4.2.1 Literals. Characters inside a CDataSection, including special characters such as < and &, are treated as literal characters rather than as markup characters (except for the sequence ]]>, which terminates the CDataSection).

    3. Each consecutive sequence of literal characters evaluates to a single text node containing the characters.

    4. Each nested direct constructor is evaluated according to the rules in 4.12.1 Direct Element Constructors or 4.12.2 Other Direct Constructors, resulting in a new element, comment, or processing instruction node. Then:

      1. The parent property of the resulting node is then set to the newly constructed element node.

      2. The base-uri property of the resulting node, and of each of its descendants, is set to be the same as that of its new parent, unless it (the child node) has an xml:base attribute, in which case its base-uri property is set to the value of that attribute, resolved (if it is relative) against the base-uri property of its new parent node.

    5. Enclosed expressions are evaluated as follows:

      1. Each array returned by the enclosed expression is flattened by calling the function array:flatten() before the steps that follow.

      2. If an enclosed expression returns a function item, a type error is raised [err:XQTY0105].

      3. For each adjacent sequence of one or more atomic items returned by an enclosed expression, a new text node is constructed, containing the result of casting each atomic item to a string, with a single space character inserted between adjacent values.

        Note:

        The insertion of blank characters between adjacent values applies even if one or both of the values is a zero-length string.

      4. For each node returned by an enclosed expression, a new copy is made of the given node and all nodes that have the given node as an ancestor, collectively referred to as copied nodes. The properties of the copied nodes are as follows:

        1. Each copied node receives a new node identity.

        2. The parent, children, and attributes properties of the copied nodes are set so as to preserve their inter-node relationships. For the topmost node (the node directly returned by the enclosed expression), the parent property is set to the node constructed by this constructor.

        3. If construction mode in the static context is strip:

          1. If the copied node is an element node, its type annotation is set to xs:untyped. Its nilled, is-id, and is-idrefs properties are set to false.

          2. If the copied node is an attribute node, its type-name property is set to xs:untypedAtomic. Its is-idrefs property is set to false. Its is-id property is set to true if the qualified name of the attribute node is xml:id; otherwise it is set to false.

          3. The string-value of each copied element and attribute node remains unchanged, and its typed-value becomes equal to its string-value as an instance of xs:untypedAtomic.

            Note:

            Implementations that store only the typed value of a node are required at this point to convert the typed value to a string form.

          On the other hand, if construction mode in the static context is preserve, the type-name, nilled, string-value, typed-value, is-id, and is-idrefs properties of the copied nodes are preserved.

        4. The in-scope-namespaces property of a copied element node is determined by the following rules. In applying these rules, the default namespace or absence of a default namespace is treated like any other namespace binding:

          1. If copy-namespaces mode specifies preserve, all in-scope-namespaces of the original element are retained in the new copy. If copy-namespaces mode specifies no-preserve, the new copy retains only those in-scope namespaces of the original element that are used in the names of the element and its attributes.

          2. If copy-namespaces mode specifies inherit, the copied node inherits all the in-scope namespaces of the constructed node, augmented and overridden by the in-scope namespaces of the original element that were preserved by the preceding rule. If copy-namespaces mode specifies no-inherit, the copied node does not inherit any in-scope namespaces from the constructed node.

        5. An enclosed expression in the content of an element constructor may cause one or more existing nodes to be copied. Type error [err:XQTY0086] is raised in the following cases:

          1. An element node is copied, and the typed value of the element node or one of its attributes is namespace-sensitive, and construction mode is preserve, and copy-namespaces mode is no-preserve.

          2. An attribute node is copied but its parent element node is not copied, and the typed value of the copied attribute node is namespace-sensitive, and construction mode is preserve.

          Note:

          The rationale for error [err:XQTY0086] is as follows: It is not possible to preserve the type of a QName without also preserving the namespace binding that defines the prefix of the QName.

        6. When an element or processing instruction node is copied, its base-uri property is set to be the same as that of its new parent, with the following exception: if a copied element node has an xml:base attribute, its base-uri property is set to the value of that attribute, resolved (if it is relative) against the base-uri property of the new parent node.

        7. All other properties of the copied nodes are preserved.

  2. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  3. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  4. If the content sequence contains an attribute node or a namespace node following a node that is not an attribute node or a namespace node, a type error is raised [err:XQTY0024].

  5. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from resolving the element name in the start tag, including its original namespace prefix (if any), as described in 4.12.1 Direct Element Constructors.

    2. parent is set to empty.

    3. attributes consist of all the attributes specified in the start tag as described in 4.12.1.1 Attributes, together with all the attribute nodes in the content sequence, in implementation-dependent order. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node. If two or more attributes have the same node-name, a dynamic error is raised [err:XQDY0025]. If an attribute named xml:space has a value other than preserve or default, a dynamic error may be raised [err:XQDY0092].

    4. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.

    5. base-uri is set to the following value:

      1. If the constructed node has an attribute named xml:base, then the value of this attribute, resolved (if it is relative) against the Executable Base URI, as described in 2.5.6 Resolving a Relative URI Reference.

      2. Otherwise, the Executable Base URI.

    6. in-scope-namespaces consist of all the namespace bindings resulting from namespace declaration attributes as described in 4.12.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 4.12.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order. If there are no text-node descendants, the string-value property is a zero-length string.

    9. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

    10. If construction mode in the static context is strip, the type-name property is xs:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.

    11. The is-id and is-idrefs properties are set to false.

  • Example:

    <a>{ 1 }</a>

    The constructed element node has one child, a text node containing the value "1".

  • Example:

    <a>{ 1, 2, 3 }</a>

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <c>{ 1 }{ 2 }{ 3 }</c>

    The constructed element node has one child, a text node containing the value "123".

  • Example:

    <b>{ 1, "2", "3" }</b>

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <fact>I saw 8 cats.</fact>

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw { 5 + 3 } cats.</fact>

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw <howmany>{ 5 + 3 }</howmany> cats.</fact>

    The constructed element node has three children: a text node containing "I saw ", a child element node named howmany, and a text node containing " cats.". The child element node in turn has a single text node child containing the value "8".

4.12.1.4 Boundary Whitespace

In a direct element constructor, whitespace characters may appear in the content of the constructed element. In some cases, enclosed expressions and/or nested elements may be separated only by whitespace characters. For example, in the expression below, the end-tag </title> and the start-tag <author> are separated by a newline character and four space characters:

<book isbn="isbn-0060229357">
  <title>Harold and the Purple Crayon</title>
  <author>
    <first>Crockett</first>
    <last>Johnson</last>
  </author>
</book>

[Definition: Boundary whitespace is a sequence of consecutive whitespace characters within the content of a direct element constructor, that is delimited at each end either by the start or end of the content, or by a DirectConstructor, or by an EnclosedExpr. For this purpose, characters generated by character references such as &#x20; or by CDataSections are not considered to be whitespace characters.]

The boundary-space policy in the static context controls whether boundary whitespace is preserved by element constructors. If boundary-space policy is strip, boundary whitespace is not considered significant and is discarded. On the other hand, if boundary-space policy is preserve, boundary whitespace is considered significant and is preserved.

  • Example:

    <cat>
      <breed>{ $b }</breed>
      <color>{ $c }</color>
    </cat>

    The constructed cat element node has two child element nodes named breed and color. Whitespace surrounding the child elements will be stripped away by the element constructor if boundary-space policy is strip.

  • Example:

    <a> { "abc" } </a>

    If boundary-space policy is strip, this example is equivalent to <a>abc</a>. However, if boundary-space policy is preserve, this example is equivalent to <a>  abc  </a>.

  • Example:

    <a> z { "abc" }</a>

    Since the whitespace surrounding the z is not boundary whitespace, it is always preserved. This example is equivalent to <a> z abc</a>.

  • Example:

    <a>&#x20;{ "abc" }</a>

    This example is equivalent to <a> abc</a>, regardless of the boundary-space policy, because the space generated by the character reference is not treated as a whitespace character.

  • Example:

    <a>{ "  " }</a>

    This example constructs an element containing two space characters, regardless of the boundary-space policy, because whitespace inside an enclosed expression is never considered to be boundary whitespace.

  • Example:

    <a>{ [ "one", "little", "fish" ] }</a>

    This example constructs an element containing the text one little fish, because the array is flattened, and the resulting sequence of atomic items is converted to a text node with a single blank between values.

Note:

Element constructors treat attributes named xml:space as ordinary attributes. An xml:space attribute does not affect the handling of whitespace by an element constructor.

4.12.2 Other Direct Constructors

XQuery allows an expression to generate a processing instruction node or a comment node. This can be accomplished by using a direct processing instruction constructor or a direct comment constructor. In each case, the syntax of the constructor expression is based on the syntax of a similar construct in XML.

DirPIConstructor::="<?" PITarget (SDirPIContents)? "?>"
/* ws: explicit */
DirPIContents::=(Char* - (Char* '?>' Char*))
/* ws: explicit */
DirCommentConstructor::="<!--" DirCommentContents "-->"
/* ws: explicit */
DirCommentContents::=((Char - '-') | ('-' (Char - '-')))*
/* ws: explicit */

A direct processing instruction constructor creates a processing instruction node whose target property is PITarget and whose content property is DirPIContents. The base-uri property of the node is empty. The parent property of the node is empty.

The PITarget of a processing instruction must not consist of the characters XML in any combination of upper and lower case, and must not contain a colon. The DirPIContents of a processing instruction must not contain the string "?>".

The following example illustrates a direct processing instruction constructor:

<?format role="output" ?>

A direct comment constructor creates a comment node whose content property is DirCommentContents. Its parent property is empty.

The DirCommentContents of a comment must not contain two consecutive hyphens or end with a hyphen. These rules are syntactically enforced by the grammar shown above.

The following example illustrates a direct comment constructor:

<!-- Tags are ignored in the following section -->

Note:

A direct comment constructor is different from a comment, since a direct comment constructor actually constructs a comment node, whereas a comment is simply used in documenting a query and is not evaluated.

4.12.3 Computed Constructors

ComputedConstructor::=CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompNamespaceConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor

An alternative way to create nodes is by using a computed constructor. A computed constructor begins with a keyword that identifies the type of node to be created: element, attribute, document, text, processing-instruction, comment, or namespace.

For those kinds of nodes that have names (element, attribute, processing instruction, and namespace nodes), the keyword that specifies the node kind is followed by the name of the node to be created. This name may be specified either as an EQName or as an expression enclosed in braces. [Definition: When an expression is used to specify the name of a constructed node, that expression is called the name expression of the constructor.]

The following example illustrates the use of computed element and attribute constructors in a simple case where the names of the constructed nodes are constants. This example generates exactly the same result as the first example in 4.12.1 Direct Element Constructors:

element book {
  attribute isbn { "isbn-0060229357" },
  element title { "Harold and the Purple Crayon" },
  element author {
    element first { "Crockett" },
    element last { "Johnson" }
  }
}

Note:

XQuery 4.0 allows the node name to be written in quotation marks (for example, element "book" {}, and at the same time it disallows the use of a defined set of language keywords without quotes: for example element div {} was allowed in XQuery 3.1 but must now be written element "div" {} or element { "div" } {}. The reason for this incompatible change is that allowing map constructors to omit the map keyword would otherwise create an ambiguity: consider for example the expression element otherwise {}.

Because the list of reserved keywords may be extended in future versions of this specification, the safest strategy is to always to use quotation marks (for example element "div") when the node name is a simple NCName. To avoid any dependency on the default namespace context, the form element Q{}div might also be used.

To write code that is portable between XQuery 3.1 and XQuery 4.0, the best advice is to use either the form element { "div" } or the form element Q{}div.

4.12.3.1 Computed Element Constructors

Changes in 4.0  

  1. When the element name matches a language keyword such as div or value, it must now be written in quotes as a string literal. This is a backwards incompatible change.   [Issue 1450 PR 1480 3 October 2024]

CompElemConstructor::="element" CompNodeNameEnclosedContentExpr
CompNodeName::=StringLiteral | UnreservedName | ("{" Expr "}")
UnreservedName::=EQName
/* xgc: unreserved-name */
EnclosedContentExpr::=EnclosedExpr
EnclosedExpr::="{" Expr? "}"

[Definition: A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.]

The element name is determined by the CompNodeName, which may be provided in a number of ways:

  1. As a string literal, for example element "para" {}. The content of the string literal must take the form of an EQName: examples are "p", "html:p", "Q{}p", or "Q{http://www.w3.org/1999/xhtml}p" [err:XQST0151]. Namespace prefixes are resolved in the same way as for an EQName written without quotation marks (see below).

  2. As a simple unprefixed NCName, for example element para {}. This form is allowed only if the element name is not a reserved keyword: see unreserved-name. The name is implicitly qualified by the namespace URI that is bound to the zero-length prefix in the statically known namespaces; if there is no such binding, the expanded name will be in no namespace.

  3. As a prefixed QName (for example element html:p {}). The prefix is expanded using the statically known namespaces. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

  4. As a BracedURILiteral (for example element Q{http://www.w3.org/1999/xhtml}p {}).

  5. As an expression in curly brackets. This is processed as follows:

    1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic item of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

    2. If the atomized value of the name expression is of type xs:QName, that expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName.

    3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QNameas follows:

      1. Leading and trailing whitespace is removed.

      2. If the value is an unprefixed NCName, the name is implicitly qualified by the namespace URI that is bound to the zero-length prefix in the statically known namespaces; if there is no such binding, the expanded name will be in no namespace..

      3. If the value is a lexical QName with a prefix, that prefix is resolved to a namespace URI using the statically known namespaces.

      4. If the value is a URI-qualified name (Q{uri}local), it is converted to an expanded QName with the supplied namespace URI and local name, and with no prefix.

      Note:

      This was under-specified in XQuery 3.1.

    4. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

The resulting expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName (or its absence).

An error is raised [err:XQDY0096] if the node-name of the constructed element node has any of the following properties:

  • Its namespace prefix is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

The above error may be raised as a static error if the element name is computed statically; in other cases it must be raised as a dynamic error.

The content expression of a computed element constructor (if present) is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1e of 4.12.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. If the content expression is absent, the content sequence is an empty sequence.

Processing of the computed element constructor proceeds as follows:

  1. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  3. If the content sequence contains an attribute node or a namespace node following a node that is not an attribute node or a namespace node, a type error is raised [err:XQTY0024].

  4. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from processing the specified CompNodeName, as described above.

    2. parent is empty.

    3. attributes consist of all the attribute nodes in the content sequence, in implementation-dependent order. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node. If two or more attributes have the same node-name, a dynamic error is raised [err:XQDY0025]. If an attribute named xml:space has a value other than preserve or default, a dynamic error may be raised [err:XQDY0092].

    4. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.

    5. base-uri is set to the following value:

      1. If the constructed node has an attribute named xml:base, then the value of this attribute, resolved (if it is relative) against the Executable Base URI, as described in 2.5.6 Resolving a Relative URI Reference.

      2. Otherwise, the Executable Base URI.

    6. in-scope-namespaces are computed as described in 4.12.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    9. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

    10. If construction mode in the static context is strip, the type-name property is xs:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.

    11. The is-id and is-idrefs properties are set to false.

A computed element constructor might be used to make a modified copy of an existing element. For example, if the variable $e is bound to an element with numeric content, the following constructor might be used to create a new element with the same name and attributes as $e and with numeric content equal to twice the value of $e:

element { node-name($e) } { $e/@*, 2 * data($e) }

In this example, if $e is bound by the expression let $e := <length units="inches">{ 5 }</length>, then the result of the example expression is the element <length units="inches">10</length>.

Note:

The static type of the expression fn:node-name($e) is xs:QName?, denoting zero or one QName. The example can be successfully evaluated as written provided that $e is bound to exactly one element node with numeric content.

One important purpose of computed constructors is to allow the name of a node to be computed. We will illustrate this feature by an expression that translates the name of an element from one language to another. Suppose that the variable $dict is bound to a dictionary element containing a sequence of entry elements, each of which encodes translations for a specific word. Here is an example entry that encodes the German and Italian variants of the word “address”:

<entry word="address">
  <variant xml:lang="de">Adresse</variant>
  <variant xml:lang="it">indirizzo</variant>
</entry>

Suppose further that the variable $e is bound to the following element:

<address>123 Roosevelt Ave. Flushing, NY 11368</address>

Then the following expression generates a new element in which the name of $e has been translated into Italian and the content of $e (including its attributes, if any) has been preserved. The first enclosed expression after the element keyword generates the name of the element, and the second enclosed expression generates the content and attributes:

element {
  $dict/entry[@word = name($e)]/variant[@xml:lang = "it"]
} {
  $e/@*, $e/node()
}

The result of this expression is as follows:

<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>
4.12.3.2 Computed Attribute Constructors

Changes in 4.0  

  1. When the attribute name matches a language keyword such as by or of, it must now be written in quotes as a string literal. This is a backwards incompatible change.   [Issue 1450 PR 1480 3 October 2024]

CompAttrConstructor::="attribute" CompNodeNameEnclosedExpr
CompNodeName::=StringLiteral | UnreservedName | ("{" Expr "}")
UnreservedName::=EQName
/* xgc: unreserved-name */
EnclosedExpr::="{" Expr? "}"

A computed attribute constructor creates a new attribute node, with its own node identity.

Attributes have no default namespace. The rules that expand attribute names create an implementation-dependent prefix if an attribute name has a namespace URI but no prefix is provided.

The attribute name may be provided in a number of ways:

  1. As a string literal, for example attribute "href" {}. The content of the string literal must take the form of an EQName: examples are "href", "xlink:href", "Q{}href", or "Q{http://www.w3.org/1999/xlink}href" [err:XQST0151]. Namespace prefixes are resolved in the same way as for an EQName written without quotation marks.

  2. As a simple unprefixed NCName, for example attribute href {}. This form is allowed only if the attribute name is not a reserved keyword: see unreserved-name. The expanded attribute name will be in no namespace.

  3. As a prefixed QName (for example attribute xlink:href {}). The prefix is expanded using the statically known namespaces. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

  4. As a BracedURILiteral (for example attribute Q{http://www.w3.org/1999/xlink}href {}).

  5. As an expression in curly brackets. This is processed as follows:

    1. Atomization is applied to the result of the name expression. If the result of atomization is not a single atomic item of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

    2. If the atomized value of the name expression is of type xs:QName:

      1. If the expanded QName returned by the atomized name expression has a namespace URI but has no prefix, it is given an implementation-dependent prefix.

      2. The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node.

    3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QNameas follows:

      1. Leading and trailing whitespace is removed.

      2. If the value is an unprefixed NCName, it is treated as a local name in no namespace.

      3. If the value is a lexical QName with a prefix, that prefix is resolved to a namespace URI using the statically known namespaces.

      4. If the value is a URI-qualified name (Q{uri}local), it is converted to an expanded QName with the supplied namespace URI and local name, and with an implementation dependent prefix.

      5. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

      Note:

      This was under-specified in XQuery 3.1.

The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

If the keyword attribute is followed by a name expression, the name expression is processed as follows:

A dynamic error is raised [err:XQDY0044] if the node-name of the constructed attribute node has any of the following properties:

  • Its namespace prefix is xmlns.

  • It has no namespace prefix and its local name is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

The content expression of a computed attribute constructor is processed as follows:

  1. Atomization is applied to the result of the content expression, converting it to a sequence of atomic items. (If the content expression is absent, the result of this step is an empty sequence.)

  2. If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the string-value property of the new attribute node. The type annotation (type-name property) of the new attribute node is xs:untypedAtomic. The typed-value property of the attribute node is the same as its string-value, as an instance of xs:untypedAtomic.

  4. The parent property of the attribute node is set to empty.

  5. If the attribute name is xml:id, then xml:id processing is performed as defined in [XML ID]. This ensures that the attribute node has the type xs:ID and that its value is properly normalized. If an error is encountered during xml:id processing, an implementation may raise a dynamic error [err:XQDY0091].

  6. If the attribute name is xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.

  7. If the attribute name is xml:space and the attribute value is other than preserve or default, a dynamic error may be raised [err:XQDY0092].

  • Example:

    attribute size { 4 + 3 }

    The string value of the size attribute is "7" and its type is xs:untypedAtomic.

  • Example:

    attribute {
      if ($sex = "M") then "husband" else "wife"
    } {
      <a>Hello</a>, 1 to 3, <b>Goodbye</b>
    }

    The name of the constructed attribute is either husband or wife. Its string value is "Hello 1 2 3 Goodbye".

4.12.3.3 Document Node Constructors
CompDocConstructor::="document" EnclosedExpr
EnclosedExpr::="{" Expr? "}"

All document node constructors are computed constructors. The result of a document node constructor is a new document node, with its own node identity.

A document node constructor is useful when the result of a query is to be a document in its own right. The following example illustrates a query that returns an XML document containing a root element named author-list:

document {
  <author-list>{
    doc("bib.xml")/bib/book/author
  }</author-list>
}

The content expression of a document node constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1e of 4.12.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the document node constructor then proceeds as follows:

  1. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  3. If the content sequence contains an attribute node, a type error is raised [err:XPTY0004].

  4. If the content sequence contains a namespace node, a type error is raised [err:XPTY0004].

  5. The properties of the newly constructed document node are determined as follows:

    1. base-uri is set to the Executable Base URI.

    2. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed document node.

    3. The unparsed-entities and document-uri properties are empty.

    4. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    5. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

No validation is performed on the constructed document node. The [XML 1.0] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.

4.12.3.4 Text Node Constructors
CompTextConstructor::="text" EnclosedExpr
EnclosedExpr::="{" Expr? "}"

All text node constructors are computed constructors. The result of a text node constructor is a new text node, with its own node identity.

The content expression of a text node constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic items.

  2. If the result of atomization is an empty sequence, no text node is constructed. Otherwise, each atomic item in the atomized sequence is cast into a string.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content property of the constructed text node.

The parent property of the constructed text node is set to empty.

Note:

It is possible for a text node constructor to construct a text node containing a zero-length string. However, if used in the content of a constructed element or document node, such a text node will be deleted or merged with another text node.

The following example illustrates a text node constructor:

text { "Hello" }
4.12.3.5 Computed Processing Instruction Constructors

Changes in 4.0  

  1. When the processing instruction name matches a language keyword such as try or validate, it must now be written in quotes as a string literal. This is a backwards incompatible change.   [Issue 1512 PR 1513 18 October 2024]

CompPIConstructor::="processing-instruction" CompNodeNCNameEnclosedExpr
CompNodeNCName::=StringLiteral | UnreservedNCName | ("{" Expr "}")
UnreservedNCName::=NCName
/* xgc: unreserved-name */
EnclosedExpr::="{" Expr? "}"

A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity.

The name of a processing-instruction node is always an NCName, and may be provided in a number of ways:

  1. As a string literal, for example processing-instruction "xref" {}. The content of the string literal must take the form of an NCName.

  2. As a simple NCName, for example processing-instruction xref {}. This form is allowed only if the name is not a reserved keyword: see unreserved-name.

  3. As an expression in curly braces. This is processed as follows:

    1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic item of type xs:NCName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

    2. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is cast to the type xs:NCName. If the value cannot be cast to xs:NCName, a dynamic error is raised [err:XQDY0041].

    3. The resulting NCName is then used as the target property of the newly constructed processing instruction node. However, a dynamic error is raised if the NCName is equal to "XML" (in any combination of upper and lower case) [err:XQDY0064].

The content expression of a computed processing instruction constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic items. (If the content expression is absent, the result of this step is an empty sequence.)

  2. If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string. If any of the resulting strings contains the string "?>", a dynamic error [err:XQDY0026] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. Leading whitespace is removed from the resulting string. The resulting string then becomes the content property of the constructed processing instruction node.

The remaining properties of the new processing instruction node are determined as follows:

  1. The parent property is empty.

  2. The base-uri property is empty.

The following example illustrates a computed processing instruction constructor:

let $target := "audio-output",
return processing-instruction { $target } { "beep" }

The processing instruction node constructed by this example might be serialized as follows:

<?audio-output beep?>
4.12.3.6 Computed Comment Constructors
CompCommentConstructor::="comment" EnclosedExpr
EnclosedExpr::="{" Expr? "}"

A computed comment constructor (CompCommentConstructor) constructs a new comment node with its own node identity. The content expression of a computed comment constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic items.

  2. If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content property of the constructed comment node.

  4. It is a dynamic error [err:XQDY0072] if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.

The parent property of the constructed comment node is set to empty.

The following example illustrates a computed comment constructor:

let $homebase := "Houston"
return comment { concat($homebase, ", we have a problem.") }

The comment node constructed by this example might be serialized as follows:

<!--Houston, we have a problem.-->
4.12.3.7 Computed Namespace Constructors

Changes in 4.0  

  1. When the namespace prefix matches a language keyword such as as or at, it must now be written in quotes as a string literal. This is a backwards incompatible change.   [Issue 1512 PR 1513 18 October 2024]

CompNamespaceConstructor::="namespace" CompNodeNCNameEnclosedExpr
CompNodeNCName::=StringLiteral | UnreservedNCName | ("{" Expr "}")
UnreservedNCName::=NCName
/* xgc: unreserved-name */
EnclosedExpr::="{" Expr? "}"

A computed namespace constructor creates a new namespace node, with its own node identity. The parent of the newly created namespace node is absent.

The name of a namespace node is always an NCName, and represents the namespace prefix.

The string value of a namespace node should be a URI, and represents the namespace URI.

The namespace prefix may be provided in a number of ways:

  1. As a string literal, for example namespace "xlink" { "http://www.w3.org/1999/xlink" }. The content of the string literal must either take the form of an NCName, or must be a zero-length string.

  2. As a simple NCName, for example namespace xlink { "http://www.w3.org/1999/xlink" }. This form is allowed only if the namespace prefix is not a reserved keyword: see unreserved-name.

  3. As an expression in curly braces. This is processed as follows:

    1. Atomization is applied to the result of the enclosed expression.

    2. If the result of atomization is an empty sequence or a single atomic item of type xs:string or xs:untypedAtomic, then the following rules are applied in order:

      1. If the result is castable to xs:NCName, then it is used as the local name of the newly constructed namespace node. (The local name of a namespace node represents the prefix part of the namespace binding.)

      2. If the result is the empty sequence or a zero-length xs:string or xs:untypedAtomic item, the new namespace node has no name (such a namespace node represents a binding for the default namespace).

      3. Otherwise, a dynamic error is raised [err:XQDY0074].

    3. If the result of atomization is not an empty sequence or a single atomic item of type xs:string or xs:untypedAtomic, a type error is raised [err:XPTY0004].

The content expression is evaluated, and the result is cast to xs:anyURI to create the URI property for the newly created node. An implementation may raise a dynamic error [err:XQDY0074] if the URIExpr of a computed namespace constructor is not a valid instance of xs:anyURI.

An error [err:XQDY0101] is raised if a computed namespace constructor attempts to do any of the following:

  • Bind the prefix xml to some namespace URI other than http://www.w3.org/XML/1998/namespace.

  • Bind a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • Bind the prefix xmlns to any namespace URI.

  • Bind a prefix to the namespace URI http://www.w3.org/2000/xmlns/.

  • Bind any prefix (including the empty prefix) to a zero-length namespace URI.

By itself, a computed namespace constructor has no effect on in-scope namespaces, but if an element constructor’s content sequence contains a namespace node, the namespace binding it represents is added to the element’s in-scope namespaces.

A computed namespace constructor has no effect on the statically known namespaces.

Note:

The newly created namespace node has all properties defined for a namespace node in the data model, but its parent is always absent. As defined in the data model, the name of the node is the prefix, the string value of the node is the URI. Since the nodes are parentless, their relative order is implementation dependent.

Examples:

  • A computed namespace constructor with a prefix:

    namespace a { "http://a.example.com" }
  • A computed namespace constructor with a prefix expression:

    namespace { "a" } { "http://a.example.com" }
  • A computed namespace constructor with an empty prefix:

    namespace "" { "http://a.example.com" }

Computed namespace constructors are generally used to add to the in-scope namespaces of elements created with element constructors:

<age xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> {
  namespace xs { "http://www.w3.org/2001/XMLSchema" },
  attribute xsi:type { "xs:integer" },
  23
}</age>

In the above example, note that the xsi namespace binding is created for the element because it is used in an attribute name. The attribute’s content is simply character data, and has no effect on namespace bindings. The computed namespace constructor ensures that the xs binding is created.

Computed namespace constructors have no effect on the statically known namespaces. If the prefix a is not already defined in the statically known namespaces, the following expression results in a static error [err:XPST0081].

<a:form>{
  namespace a { "http://a.example.com" }
}</a:form>

4.12.4 In-scope Namespaces of a Constructed Element

An element node constructed by a direct or computed element constructor has an in-scope namespaces property that consists of a set of namespace bindings. The in-scope namespaces of an element node may affect the way the node is serialized (see 2.3.5 Serialization), and may also affect the behavior of certain functions that operate on nodes, such as fn:name. Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression. Also note that one of the namespace bindings in the in-scope namespaces may have no prefix (denoting the default namespace for the given element). The in-scope namespaces of a constructed element node consist of the following namespace bindings:

  • A namespace binding is created for each namespace declared in the current element constructor by a namespace declaration attribute.

  • A namespace binding is created for each namespace node in the content sequence of the current element constructor.

  • A namespace binding is created for each namespace that is declared in a namespace declaration attribute of an enclosing direct element constructor and not overridden by the current element constructor or an intermediate constructor.

  • A namespace binding is always created to bind the prefix xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • For each prefix used in the name of the constructed element or in the names of its attributes, a namespace binding must exist. If a namespace binding does not already exist for one of these prefixes, a new namespace binding is created for it. If this would result in a conflict, because it would require two different bindings of the same prefix, then the prefix used in the node name is changed to an arbitrary implementation-dependent prefix that does not cause such a conflict, and a namespace binding is created for this new prefix. If there is an in-scope default namespace, then a binding is created between the empty prefix and that URI.

Note:

Copy-namespaces mode does not affect the namespace bindings of a newly constructed element node. It applies only to existing nodes that are copied by a constructor expression.

In an element constructor, if two or more namespace bindings in the in-scope bindings would have the same prefix, then an error is raised if they have different URIs [err:XQDY0102]; if they would have the same prefix and URI, duplicate bindings are ignored. If the name of an element in an element constructor is in no namespace, creating a default namespace for that element using a computed namespace constructor is an error [err:XQDY0102]. For instance, the following computed constructor raises an error because the element’s name is not in a namespace, but a default namespace is defined.

element e { namespace { '' } { 'u' } }

The following query illustrates the in-scope namespaces of a constructed element:

declare namespace p = "http://example.com/ns/p";
declare namespace q = "http://example.com/ns/q";
declare namespace f = "http://example.com/ns/f";

<p:a q:b="{ f:func(2) }" xmlns:r="http://example.com/ns/r"/>

The in-scope namespaces of the resulting p:a element consists of the following namespace bindings:

  • p = "http://example.com/ns/p"

  • q = "http://example.com/ns/q"

  • r = "http://example.com/ns/r"

  • xml = "http://www.w3.org/XML/1998/namespace"

The namespace bindings for p and q are added to the result element because their respective namespaces are used in the names of the element and its attributes. The namespace binding r="http://example.com/ns/r" is added to the in-scope namespaces of the constructed element because it is defined by a namespace declaration attribute, even though it is not used in a name.

No namespace binding corresponding to f="http://example.com/ns/f" is created, because the namespace prefix f appears only in the query prolog and is not used in an element or attribute name of the constructed node. This namespace binding does not appear in the query result, even though it is present in the statically known namespaces and is available for use during processing of the query.

Note that the following constructed element, if nested within a validate expression, cannot be validated:

<p xsi:type="xs:integer">3</p>

The constructed element will have namespace bindings for the prefixes xsi (because it is used in a name) and xml (because it is defined for every constructed element node). During validation of the constructed element, the validator will be unable to interpret the namespace prefix xs because it is has no namespace binding. Validation of this constructed element could be made possible by providing a namespace declaration attribute, as in the following example:

<p xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:integer">3</p>

4.13 FLWOR Expressions

XQuery provides a versatile expression called a FLWOR expression that may contain multiple clauses. The FLWOR expression can be used for many purposes, including iterating over sequences, joining multiple documents, and performing grouping and aggregation. The name FLWOR, pronounced "flower", is suggested by the keywords for, let, where, order by, and return, which introduce some of the clauses used in FLWOR expressions (but this is not a complete list of such clauses.)

The complete syntax of a FLWOR expression is shown here, and relevant parts of the syntax are repeated in subsequent sections of this document.

FLWORExpr::=InitialClauseIntermediateClause* ReturnClause
InitialClause::=ForClause | LetClause | WindowClause
IntermediateClause::=InitialClause | WhereClause | WhileClause | GroupByClause | OrderByClause | CountClause
ForClause::="for" (ForBinding ++ ",")
ForBinding::=ForItemBinding | ForMemberBinding | ForEntryBinding
ForItemBinding::=VarNameAndTypeAllowingEmpty? PositionalVar? "in" ExprSingle
ForMemberBinding::="member" VarNameAndTypePositionalVar? "in" ExprSingle
ForEntryBinding::=((ForEntryKeyBindingForEntryValueBinding?) | ForEntryValueBinding) PositionalVar? "in" ExprSingle
ForEntryKeyBinding::="key" VarNameAndType
ForEntryValueBinding::="value" VarNameAndType
LetClause::="let" (LetBinding ++ ",")
LetBinding::=VarNameAndType ":=" ExprSingle
VarNameAndType::="$" EQNameTypeDeclaration?
TypeDeclaration::="as" SequenceType
AllowingEmpty::="allowing" "empty"
PositionalVar::="at" VarName
WindowClause::="for" (TumblingWindowClause | SlidingWindowClause)
TumblingWindowClause::="tumbling" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition?
SlidingWindowClause::="sliding" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition
WindowStartCondition::="start" WindowVars ("when" ExprSingle)?
WindowEndCondition::="only"? "end" WindowVars ("when" ExprSingle)?
WindowVars::=CurrentVar? PositionalVar? PreviousVar? NextVar?
CurrentVar::=VarName
PreviousVar::="previous" VarName
NextVar::="next" VarName
CountClause::="count" VarName
WhereClause::="where" ExprSingle
WhileClause::="while" ExprSingle
GroupByClause::="group" "by" (GroupingSpec ++ ",")
GroupingSpec::=VarName (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
OrderByClause::="stable"? "order" "by" OrderSpec ("," OrderSpec)*
OrderSpec::=ExprSingleOrderModifier
OrderModifier::=("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?
ReturnClause::="return" ExprSingle

The semantics of FLWOR expressions are based on a concept called a tuple stream. [Definition: A tuple stream is an ordered sequence of zero or more tuples.] [Definition: A tuple is a set of zero or more named variables, each of which is bound to a value that is an XDM instance.] Each tuple stream is homogeneous in the sense that all its tuples contain variables with the same names and the same static types. The following example illustrates a tuple stream consisting of four tuples, each containing three variables named $x, $y, and $z:

($x = 1003, $y = "Fred", $z = <age>21</age>)
($x = 1017, $y = "Mary", $z = <age>35</age>)
($x = 1020, $y = "Bill", $z = <age>18</age>)
($x = 1024, $y = "John", $z = <age>29</age>)

Note:

In this section, tuple streams are represented as shown in the above example. Each tuple is on a separate line and is enclosed in parentheses, and the variable bindings inside each tuple are separated by commas. This notation does not represent XQuery syntax, but is simply a representation of a tuple stream for the purpose of defining the semantics of FLWOR expressions.

Tuples and tuple streams are not part of the data model. They exist only as conceptual intermediate results during the processing of a FLWOR expression.

Conceptually, the first clause generates a tuple stream. Each clause between the first clause and the return clause takes the tuple stream generated by the previous clause as input and generates a (possibly different) tuple stream as output. The return clause takes a tuple stream as input and, for each tuple in this tuple stream, generates an XDM instance; the final result of the FLWOR expression is the ordered concatenation of these XDM instances.

The initial clause in a FLWOR expression may be a for, let, or window clause. Intermediate clauses may be for, let, window, count, where, group by, or order by clauses. These intermediate clauses may be repeated as many times as desired, in any order. The final clause of the FLWOR expression must be a return clause. The semantics of the various clauses are described in the following sections.

4.13.1 Variable Bindings

The following clauses in FLWOR expressions bind values to variables: for, let, window, count, and group by. The binding of variables for for, let, and count is governed by the following rules (the binding of variables in group by is discussed in 4.13.8 Group By Clause, the binding of variables in window clauses is discussed in 4.13.4 Window Clause):

  1. The scope of a bound variable includes all subexpressions of the containing FLWOR that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following code fragment, containing two let clauses, illustrates how variable bindings may reference variables that were bound in earlier clauses, or in earlier bindings in the same clause:

    let $x := 47, $y := f($x)
    let $z := g($x, $y)
  2. A given variable name may be bound more than once in a FLWOR expression, or even within one clause of a FLWOR expression. In such a case, each new binding occludes the previous one, which becomes inaccessible in the remainder of the FLWOR expression.

    For example, it is valid to write:

    let $x := 0, $x := $x*2, $x := $x + 1

    This binds three separate variables, each of which happens to have the same name. It should not be construed as binding a series of different values to the same variable.

  3. [Definition: A variable binding may be accompanied by a type declaration, which consists of the keyword as followed by the static type of the variable, declared using the syntax in 3.1 Sequence Types.] The type declaration defines a required type for the value. At run-time, the supplied value for the variable is converted to the required type by applying the coercion rules. If conversion is not possible, a type error is raised [err:XPTY0004]. For example, the following let clause raises a type error because the variable $salary has a type declaration that is not satisfied by the value that is bound to it:

    let $salary as xs:decimal := "cat"

    The following let clause, however, succeeds, because the coercion rules allow an xs:decimal to be supplied where an xs:double is required:

    let $temperature as xs:double := 32.5

    In applying the coercion rules, XPath 1.0 compatibility mode does not apply.

  4. [Definition: In a for clause, when an expression is preceded by the keyword in, the value of that expression is called a binding collection.] The collection may be either a sequence, an array, or a map. The for clause iterates over its binding collection, producing multiple bindings for one or more variables. Details on how binding collections are used in for clauses are described in the following sections.

  5. [Definition: In a window clause, when an expression is preceded by the keyword in, the value of that expression is called a binding sequence.] The window clause iterates over its binding sequence, producing multiple bindings for one or more variables. Details on how binding sequences are used in for and window clauses are described in the following sections.

4.13.2 For Clause

Changes in 4.0  

  1. A for member clause is added to FLWOR expressions to allow iteration over an array.   [Issue 49 PR 344 10 February 2023]

  2. A for key/value clause is added to FLWOR expressions to allow iteration over a map.   [Issue 31 PR 1249 1 June 2024]

  3. The value bound to a variable in a for clause is now converted to the declared type by applying the coercion rules.   [Issue 189 PR 820 8 November 2023]

ForClause::="for" (ForBinding ++ ",")
ForBinding::=ForItemBinding | ForMemberBinding | ForEntryBinding
ForItemBinding::=VarNameAndTypeAllowingEmpty? PositionalVar? "in" ExprSingle
ForMemberBinding::="member" VarNameAndTypePositionalVar? "in" ExprSingle
ForEntryBinding::=((ForEntryKeyBindingForEntryValueBinding?) | ForEntryValueBinding) PositionalVar? "in" ExprSingle
ForEntryKeyBinding::="key" VarNameAndType
ForEntryValueBinding::="value" VarNameAndType
TypeDeclaration::="as" SequenceType
AllowingEmpty::="allowing" "empty"
PositionalVar::="at" VarName

A for clause is used for iteration. Each variable in a for clause iterates over a sequence, an array, or a map.

The expression following the keyword in is evaluated; we refer to the resulting sequence, array, or map generically as the binding collection, and to its items, members, or entries as the components of the collection.

  • When a ForItemBinding is used (that is, when none of the keywords member, key, or value is used), the range variable is bound in turn to each item in the binding collection, which is treated as a sequence of items.

  • When a ForMemberBinding is used (that is, when the keyword member is used), the range variable is bound in turn to each member of the array.

    In this case the corresponding ExprSingle must evaluate to a single array, otherwise a type error is raised [err:XPTY0141].

  • When a ForEntryBinding is used (that is, when either or both of the keywords key and value are used), the key range variable (if present) is bound in turn to each key in the map (in implementation dependent order), and the value range variable (if present) is bound to the corresponding value.

    In this case the corresponding ExprSingle must evaluate to a single map, otherwise a type error is raised [err:XPTY0141].

    If both the key and value variables are declared, their expanded QNames must be distinct [err:XQST0089].

If a for clause contains multiple bindings separated by commas it is semantically equivalent to multiple for clauses, each containing one of the bindings in the original for clause.

Example:

  • The clause

    for $x in $expr1, $y in $expr2

    is semantically equivalent to:

    for $x in $expr1
    for $y in $expr2
  • The clause

    for member $x in $expr1, member $y in $expr2

    is semantically equivalent to:

    for member $x in $expr1
    for member $y in $expr2

In the remainder of this section, we define the semantics of a for clause containing a single variable and an associated expression (following the keyword in) whose value is the binding collection for that variable.

If a single-variable for clause is the initial clause in a FLWOR expression, it iterates over its binding collection, binding the variable(s) to each component in turn. The resulting sequence of variable bindings becomes the initial tuple stream that serves as input to the next clause of the FLWOR expression. The order of tuples in the tuple stream preserves the order of the binding collection.

If the binding collection is empty, the output tuple stream depends on whether allowing empty is specified. If allowing empty is specified, the output tuple stream consists of one tuple in which the variable is bound to an empty sequence. This option is not available when the keywords member, key, or value are used. If allowing empty is not specified, the output tuple stream consists of zero tuples.

The following examples illustrates tuple streams that are generated by initial for clauses:

  • Initial clause:

    for $x in (100, 200, 300)

    or (equivalently):

    for $x allowing empty in (100, 200, 300)

    Output tuple stream:

    ($x = 100)
    ($x = 200)
    ($x = 300)
  • Initial clause:

    for $x in ()

    Output tuple stream contains no tuples.

  • Initial clause:

    for $x allowing empty in ()

    Output tuple stream:

    ($x = ())
  • Initial clause:

    for member $x in [ 1, 2, (5 to 10) ]

    Output tuple stream:

    ($x = (1))
    ($x = (2))
    ($x = (5, 6, 7, 8, 9, 10)
  • Initial clause:

    for member $x in []

    Output tuple stream contains no tuples.

  • Initial clause:

    for key $k value $v in { 'x': 1, 'y': 2 }

    Output tuple stream:

    ($k = 'x', $v = 1)
    ($k = 'y', $v = 2)

[Definition: A positional variable is a variable that is preceded by the keyword at.] A positional variable may be associated with the range variable(s) that are bound in a for clause. In this case, as the main range variable(s) iterate over the components of its binding collection, the positional variable iterates over the integers that represent the ordinal numbers of these component in the binding collection, starting with one. Each tuple in the output tuple stream contains bindings for both the main variable and the positional variable. If the binding collection is empty and allowing empty is specified, the positional variable in the output tuple is bound to the integer zero. Positional variables have the implied type xs:integer.

The expanded QName of a positional variable must be distinct from the expanded QName of the main variable with which it is associated [err:XQST0089].

The following examples illustrate how a positional variable would have affected the results of the previous examples that generated tuples:

  • Initial clause:

    for $x at $i in (100, 200, 300)

    Output tuple stream:

    ($x = 100, $i = 1)
    ($x = 200, $i = 2)
    ($x = 300, $i = 3)
  • Initial clause:

    for $x at $i in [1 to 3, 11 to 13, 21 to 23

    Output tuple stream:

    ($x = (1, 2, 3), $i = 1)
    ($x = (11, 12, 13), $i = 2)
    ($x = (21, 22, 23), $i = 3)
  • Initial clause:

    for $x allowing empty at $i in ()

    Output tuple stream:

    ($x = (), $i = 0)

If a single-variable for clause is an intermediate clause in a FLWOR expression, its binding collection is evaluated for each input tuple, given the bindings in that input tuple. Each input tuple generates zero or more tuples in the output tuple stream. Each of these output tuples consists of the original variable bindings of the input tuple plus a binding of the new variable to one of the items in its binding collecction.

Note:

Although the binding collection is conceptually evaluated independently for each input tuple, an optimized implementation may sometimes be able to avoid re-evaluating the binding collection if it can show that the variables that the binding collection depends on have the same values as in a previous evaluation.

For a given input tuple, if the binding collection for the new variable in the for clause is empty (that is, it is an empty sequence or an empty array depending on whether member is specified), and if allowing empty is not specified, the input tuple generates zero output tuples (it is not represented in the output tuple stream.)

The allowing empty option is available only when processing sequences, not when processing arrays or maps. The effect is that if the binding collection is an empty sequence, the input tuple generates one output tuple, with the original variable bindings plus a binding of the new variable to an empty sequence.

Note:

If a type declaration is present and allowing empty is specified, the type declaration should include an occurrence indicator of "?" to indicate that the variable may be bound to an empty sequence.

If the new variable introduced by a for clause has an associated positional variable, the output tuples generated by the for clause also contain bindings for the positional variable. In this case, as the new variable is bound to each item in its binding collection, the positional variable is bound to the ordinal position of that item within the binding collection, starting with one. Note that, since the positional variable represents a position within a binding collection, the output tuples corresponding to each input tuple are independently numbered, starting with one. For a given input tuple, if the binding collection is empty and allowing empty is specified, the positional variable in the output tuple is bound to the integer zero.

The tuples in the output tuple stream are ordered primarily by the order of the input tuples from which they are derived, and secondarily by the order of the binding sequence for the new variable; otherwise the order of the output tuple stream is implementation-dependent.

The following examples illustrates the effects of intermediate for clauses:

  • Input tuple stream:

    ($x = 1)
    ($x = 2)
    ($x = 3)
    ($x = 4)

    Intermediate for clause:

    for $y in ($x to 3)

    Output tuple stream:

    ($x = 1, $y = 1)
    ($x = 1, $y = 2)
    ($x = 1, $y = 3)
    ($x = 2, $y = 2)
    ($x = 2, $y = 3)
    ($x = 3, $y = 3)

    Note:

    In this example, there is no output tuple that corresponds to the input tuple ($x = 4) because, when the for clause is evaluated with the bindings in this input tuple, the resulting binding collection for $y is empty.

  • This example shows how the previous example would have been affected by a positional variable (assuming the same input tuple stream):

    for $y at $j in ($x to 3)

    Output tuple stream:

    ($x = 1, $y = 1, $j = 1)
    ($x = 1, $y = 2, $j = 2)
    ($x = 1, $y = 3, $j = 3)
    ($x = 2, $y = 2, $j = 1)
    ($x = 2, $y = 3, $j = 2)
    ($x = 3, $y = 3, $j = 1)
  • This example shows how the previous example would have been affected by allowing empty. Note that allowing empty causes the input tuple ($x = 4) to be represented in the output tuple stream, even though the binding sequence for $y contains no items for this input tuple. This example illustrates that allowing empty in a for clause serves a purpose similar to that of an “outer join” in a relational database query. (Assume the same input tuple stream as in the previous example.)

    for $y allowing empty at $j in ($x to 3)

    Output tuple stream:

    ($x = 1, $y = 1, $j = 1)
    ($x = 1, $y = 2, $j = 2)
    ($x = 1, $y = 3, $j = 3)
    ($x = 2, $y = 2, $j = 1)
    ($x = 2, $y = 3, $j = 2)
    ($x = 3, $y = 3, $j = 1)
    ($x = 4, $y = (), $j = 0)
  • This example illustrates processing of arrays:

    Input tuple stream:

    ($x = 1)
    ($x = 2)
    ($x = 3)

    Intermediate for clause:

    for member $y in [[$x+1, $x+2], [[$x+3, $x+4]]

    Output tuple stream:

    ($x = 1, $y = [ 2, 3 ])
    ($x = 1, $y = [ 4, 5 ])
    ($x = 2, $y = [ 3, 4 ])
    ($x = 2, $y = [ 5, 6 ])
    ($x = 3, $y = [ 4, 5 ])
    ($x = 3, $y = [ 6, 7 ])
  • This example shows how a for clause that binds two variables is semantically equivalent to two for clauses that bind one variable each. We assume that this for clause occurs at the beginning of a FLWOR expression. It is equivalent to an initial single-variable for clause that provides an input tuple stream to an intermediate single-variable for clause.

    for $x in (1, 2, 3, 4), $y in ($x to 3)

    Output tuple stream:

    ($x = 1, $y = 1)
    ($x = 1, $y = 2)
    ($x = 1, $y = 3)
    ($x = 2, $y = 2)
    ($x = 2, $y = 3)
    ($x = 3, $y = 3)

A for clause may contain one or more type declarations, identified by the keyword as. The semantics of type declarations are defined in 4.13.1 Variable Bindings.

4.13.3 Let Clause

Changes in 4.0  

  1. The value bound to a variable in a let clause is now converted to the declared type by applying the coercion rules.   [Issue 189 PR 254 29 November 2022]

LetClause::="let" (LetBinding ++ ",")
LetBinding::=VarNameAndType ":=" ExprSingle
TypeDeclaration::="as" SequenceType

The purpose of a let clause is to bind values to one or more variables. Each variable is bound to the result of evaluating an expression.

If a let clause contains multiple variables, it is semantically equivalent to multiple let clauses, each containing a single variable. For example, the clause

let $x := $expr1, $y := $expr2

is semantically equivalent to the following sequence of clauses:

let $x := $expr1
let $y := $expr2

In the remainder of this section, we define the semantics of a let clause containing a single variable V and an associated expression E.

If a single-variable let clause is the initial clause in a FLWOR expression, it simply binds the variable V to the result of the expression E. The result of the let clause is a tuple stream consisting of one tuple with a single binding that binds V to the result of E. This tuple stream serves as input to the next clause in the FLWOR expression.

If a single-variable let clause is an intermediate clause in a FLWOR expression, it adds a new binding for variable V to each tuple in the input tuple stream. For each input tuple, the value bound to V is the result of evaluating expression E, given the bindings that are already present in that input tuple. The resulting tuples become the output tuple stream of the let clause.

The number of tuples in the output tuple stream of an intermediate let clause is the same as the number of tuples in the input tuple stream. The number of bindings in the output tuples is one more than the number of bindings in the input tuples, unless the input tuples already contain bindings for V; in this case, the new binding for V occludes (replaces) the earlier binding for V, and the number of bindings is unchanged.

A let clause may contain one or more type declarations, identified by the keyword as. The semantics of type declarations are defined in 4.13.1 Variable Bindings.

The following code fragment illustrates how a for clause and a let clause can be used together. The for clause produces an initial tuple stream containing a binding for variable $d to each department number found in a given input document. The let clause adds an additional binding to each tuple, binding variable $e to a sequence of employees whose department number matches the value of $d in that tuple.

for $d in doc("depts.xml")/depts/deptno
let $e := doc("emps.xml")/emps/emp[deptno eq $d]

4.13.4 Window Clause

Changes in 4.0  

  1. The start clause in window expressions has become optional, as well as the when keyword and its associated expression.   [Issue 452 PR 483 18 May 2023]

WindowClause::="for" (TumblingWindowClause | SlidingWindowClause)
TumblingWindowClause::="tumbling" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition?
SlidingWindowClause::="sliding" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition
VarNameAndType::="$" EQNameTypeDeclaration?
WindowStartCondition::="start" WindowVars ("when" ExprSingle)?
WindowEndCondition::="only"? "end" WindowVars ("when" ExprSingle)?
WindowVars::=CurrentVar? PositionalVar? PreviousVar? NextVar?
CurrentVar::=VarName
PositionalVar::="at" VarName
PreviousVar::="previous" VarName
NextVar::="next" VarName
VarName::="$" EQName

Like a for clause, a window clause iterates over its binding sequence and generates a sequence of tuples. In the case of a window clause, each tuple represents a window. [Definition: A window is a sequence of consecutive items drawn from the binding sequence.] Each window is represented by at least one and at most nine bound variables. The variables have user-specified names, but their roles are as follows:

  • Window-variable: Bound to the sequence of items from the binding sequence that comprise the window.

  • Start-item: (Optional) Bound to the first item in the window.

  • Start-item-position: (Optional) Bound to the ordinal position of the first window item in the binding sequence. Start-item-position is a positional variable; hence, its type is xs:integer.

  • Start-previous-item: (Optional) Bound to the item in the binding sequence that precedes the first item in the window (empty sequence if none).

  • Start-next-item: (Optional) Bound to the item in the binding sequence that follows the first item in the window (empty sequence if none).

  • End-item: (Optional) Bound to the last item in the window.

  • End-item-position: (Optional) Bound to the ordinal position of the last window item in the binding sequence. End-item-position is a positional variable; hence, its type is xs:integer.

  • End-previous-item: (Optional) Bound to the item in the binding sequence that precedes the last item in the window (empty sequence if none).

  • End-next-item: (Optional) Bound to the item in the binding sequence that follows the last item in the window (empty sequence if none).

All variables in a window clause must have distinct names; otherwise a static error is raised [err:XQST0103].

The following is an example of a window clause that binds nine variables to the roles listed above. In this example, the variables are named $w, $s, $spos, $sprev, $snext, $e, $epos, $eprev, and $enext respectively. A window clause always binds the window variable, but typically binds only a subset of the other variables.

for tumbling window $w in (2, 4, 6, 8, 10)
  start $s at $spos previous $sprev next $snext when true() 
  end   $e at $epos previous $eprev next $enext when true()

Windows are created by iterating over the items in the binding sequence, in order, identifying the start item and the end item of each window by evaluating the WindowStartCondition and the WindowEndCondition. Each of these conditions is satisfied if the effective boolean value of the expression following the when keyword is true. The start item of the window is an item that satisfies the WindowStartCondition (see 4.13.4.1 Tumbling Windows and 4.13.4.2 Sliding Windows for a more complete explanation.) The end item of the window is the first item in the binding sequence, beginning with the start item, that satisfies the WindowEndCondition (again, see 4.13.4.1 Tumbling Windows and 4.13.4.2 Sliding Windows for more details.) Each window contains its start item, its end item, and all items that occur between them in the binding sequence. If the end item is the start item, then the window contains only one item. If a start item is identified, but no following item in the binding sequence satisfies the WindowEndCondition, then the only keyword determines whether a window is generated: if only end is specified, then no window is generated; otherwise, the end item is set to the last item in the binding sequence and a window is generated.

In the above example, the WindowStartCondition and WindowEndCondition are both true, which causes each item in the binding sequence to be in a separate window. Typically, the WindowStartCondition and WindowEndCondition are expressed in terms of bound variables. For example, the following WindowStartCondition might be used to start a new window for every item in the binding sequence that is larger than both the previous item and the following item:

start $s previous $sprev next $snext
when  $s > $sprev and $s > $snext

The scoping rules for the variables bound by a window clause are as follows:

  • In the when-expression of the WindowStartCondition, the following variables (identified here by their roles) are in scope (if bound): start-item, start-item-position, start-previous-item, start-next-item.

  • In the when-expression of the WindowEndCondition, the following variables (identified here by their roles) are in scope (if bound): start-item, start-item-position, start-previous-item, start-next-item, end-item, end-item-position, end-previous-item, end-next-item.

  • In the clauses of the FLWOR expression that follow the window clause, all nine of the variables bound by the window clause (including window-variable) are in scope (if bound).

The when keyword of a condition and the associated expression is optional. If omitted, the expression defaults to true(). If the complete start clause is omitted, no variables are bound and the expression also defaults to true(). The end clause can be omitted only within a TumblingWindowClause.

In a window clause, the keyword tumbling or sliding determines the way in which the starting item of each window is identified, as explained in the following sections.

4.13.4.1 Tumbling Windows

If the window type is tumbling, then windows never overlap. The search for the start of the first window begins at the beginning of the binding sequence. After each window is generated, the search for the start of the next window begins with the item in the binding sequence that occurs after the ending item of the last generated window. Thus, no item that occurs in one window can occur in another window drawn from the same binding sequence (unless the sequence contains the same item more than once). In a tumbling window clause, the end clause is optional; if it is omitted, the start clause is applied to identify all potential starting items in the binding sequence, and a window is constructed for each starting item, including all items from that starting item up to the item before the next window’s starting item, or the end of the binding sequence, whichever comes first.

The following examples illustrate the use of tumbling windows.

  • Show non-overlapping windows of three items.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      only end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>8 10 12</window>
  • Show averages of non-overlapping three-item windows.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      only end at $e when $e - $s eq 2
    return avg($w)

    Result:

    4 10
  • Show first and last items in each window of three items.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start $first at $s
      only end $last at $e when $e - $s eq 2
    return <window>{ $first, $last }</window>

    Result:

    <window>2 6</window>
    <window>8 12</window>
  • Show non-overlapping windows of up to three items (illustrates end clause without the only keyword).

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
  • Show non-overlapping windows of up to three items (illustrates use of start without explicit end).

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s when $s mod 3 = 1
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
  • Show non-overlapping sequences starting with a number divisible by 3.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      start $first when $first mod 3 = 2
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
  • Show non-overlapping sequences ending with a number divisible by 3.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
      end $last when $last mod 3 = 0
    return <window>{ $w }</window>

    Result (identical to the result of the previous query):

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
4.13.4.2 Sliding Windows

If the window type is sliding window, then windows may overlap. Every item in the binding sequence that satisfies the WindowStartCondition is the starting item of a new window. Thus, a given item may be found in multiple windows drawn from the same binding sequence.

The following examples illustrate the use of sliding windows.

  • Show windows of three items.

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      only end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>4 6 8</window>
    <window>6 8 10</window>
    <window>8 10 12</window>
    <window>10 12 14</window>
  • Show moving averages of three items.

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      only end at $e when $e - $s eq 2
    return avg($w)

    Result:

    4 6 8 10 12
  • Show overlapping windows of up to three items (illustrates end clause without the only keyword).

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
      start at $s
      end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result:

    <window>2 4 6</window>
    <window>4 6 8</window>
    <window>6 8 10</window>
    <window>8 10 12</window>
    <window>10 12 14</window>
    <window>12 14</window>
    <window>14</window>
4.13.4.3 Effects of Window Clauses on the Tuple Stream

The effects of a window clause on the tuple stream are similar to the effects of a for clause. As described in 4.13.4 Window Clause, a window clause generates zero or more windows, each of which is represented by at least one and at most nine bound variables.

If the window clause is the initial clause in a FLWOR expression, the bound variables that describe each window become an output tuple. These tuples form the initial tuple stream that serves as input to the next clause of the FLWOR expression. The order of tuples in the tuple stream is the order in which their start items appear in the binding sequence. The cardinality of the tuple stream is equal to the number of windows.

If a window clause is an intermediate clause in a FLWOR expression, each input tuple generates zero or more output tuples, each consisting of the original bound variables of the input tuple plus the new bound variables that represent one of the generated windows. For each tuple T in the input tuple stream, the output tuple stream will contain NT tuples, where NT is the number of windows generated by the window clause, given the bindings in the input tuple T. Input tuples for which no windows are generated are not represented in the output tuple stream. The order of tuples in the output stream is determined primarily by the order of the input tuples from which they were derived, and secondarily by the order in which their start items appear in the binding sequence.

The following example illustrates a window clause that is the initial clause in a FLWOR expression. The example is based on input data that consists of a sequence of closing stock prices for a specific company. For this example we assume the following input data (assume that the price elements have a validated type of xs:decimal):

<stock>
  <closing> <date>2008-01-01</date> <price>105</price> </closing>
  <closing> <date>2008-01-02</date> <price>101</price> </closing>
  <closing> <date>2008-01-03</date> <price>102</price> </closing>
  <closing> <date>2008-01-04</date> <price>103</price> </closing>
  <closing> <date>2008-01-05</date> <price>102</price> </closing>
  <closing> <date>2008-01-06</date> <price>104</price> </closing>
</stock>

A user wishes to find “run-ups,” which are defined as sequences of dates that begin with a “low” and end with a “high” price (that is, the stock price begins to rise on the first day of the run-up, and continues to rise or remain even through the last day of the run-up.) The following query uses a tumbling window to find run-ups in the input data:

for tumbling window $w in //closing
   start $first next $second when $first/price < $second/price
   end $last next $beyond when $last/price > $beyond/price
return
  <run-up>
    <start-date>{ data($first/date) }</start-date>
    <start-price>{ data($first/price) }</start-price>
    <end-date>{ data($last/date) }</end-date>
    <end-price>{ data($last/price) }</end-price>
  </run-up>

For our sample input data, this tumbling window clause generates a tuple stream consisting of two tuples, each representing a window and containing five bound variables named $w, $first, $second, $last, and $beyond. The return clause is evaluated for each of these tuples, generating the following query result:

<run-up>
  <start-date>2008-01-02</start-date>
  <start-price>101</start-price>
  <end-date>2008-01-04</end-date>
  <end-price>103</end-price>
</run-up>
<run-up>
  <start-date>2008-01-05</start-date>
  <start-price>102</start-price>
  <end-date>2008-01-06</end-date>
  <end-price>104</end-price>
</run-up>

The following example illustrates a window clause that is an intermediate clause in a FLWOR expression. In this example, the input data contains closing stock prices for several different companies, each identified by a three-letter symbol. We assume the following input data (again assuming that the type of the price element is xs:decimal):

<stocks>
  <closing> <symbol>ABC</symbol> <date>2008-01-01</date> <price>105</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-01</date> <price>057</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-02</date> <price>101</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-02</date> <price>054</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-03</date> <price>102</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-03</date> <price>056</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-04</date> <price>103</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-04</date> <price>052</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-05</date> <price>101</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-05</date> <price>055</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-06</date> <price>104</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-06</date> <price>059</price> </closing>
</stocks>

As in the previous example, we want to find "run-ups," which are defined as sequences of dates that begin with a "low" and end with a "high" price for a specific company. In this example, however, the input data consists of stock prices for multiple companies. Therefore it is necessary to isolate the stock prices of each company before forming windows. This can be accomplished by an initial for and let clause, followed by a window clause, as follows:

for $symbol in distinct-values(//symbol)
let $closings := //closing[symbol = $symbol]
for tumbling window $w in $closings
  start $first next $second when $first/price < $second/price
  end $last next $beyond when $last/price > $beyond/price
return
  <run-up symbol="{ $symbol }">
    <start-date>{ data($first/date) }</start-date>
    <start-price>{ data($first/price) }</start-price>
    <end-date>{ data($last/date) }</end-date>
    <end-price>{ data($last/price) }</end-price>
  </run-up>

Note:

In the above example, the for and let clauses could be rewritten as follows:

for $closings in //closing
let $symbol := $closings/symbol
group by $symbol

The group by clause is described in 4.13.8 Group By Clause.

The for and let clauses in this query generate an initial tuple stream consisting of two tuples. In the first tuple, $symbol is bound to "ABC" and $closings is bound to the sequence of closing elements for company ABC. In the second tuple, $symbol is bound to "DEF" and $closings is bound to the sequence of closing elements for company DEF.

The window clause operates on this initial tuple stream, generating two windows for the first tuple and two windows for the second tuple. The result is a tuple stream consisting of four tuples, each with the following bound variables: $symbol, $closings, $w, $first, $second, $last, and $beyond. The return clause is then evaluated for each of these tuples, generating the following query result:

<run-up symbol="ABC">
   <start-date>2008-01-02</start-date>
   <start-price>101</start-price>
   <end-date>2008-01-04</end-date>
   <end-price>103</end-price>
</run-up>
<run-up symbol="ABC">
   <start-date>2008-01-05</start-date>
   <start-price>101</start-price>
   <end-date>2008-01-06</end-date>
   <end-price>104</end-price>
</run-up>
<run-up symbol="DEF">
   <start-date>2008-01-02</start-date>
   <start-price>054</start-price>
   <end-date>2008-01-03</end-date>
   <end-price>056</end-price>
</run-up>
<run-up symbol="DEF">
   <start-date>2008-01-04</start-date>
   <start-price>052</start-price>
   <end-date>2008-01-06</end-date>
   <end-price>059</end-price>
</run-up>

4.13.5 Where Clause

WhereClause::="where" ExprSingle

A where clause serves as a filter for the tuples in its input tuple stream. The expression in the where clause, called the where-expression, is evaluated once for each of these tuples. If the effective boolean value of the where-expression is true, the tuple is retained in the output tuple stream; otherwise the tuple is discarded.

Examples:

  • This example illustrates the effect of a where clause on a tuple stream:

    Input tuple stream:

    ($a = 5, $b = 11)
    ($a = 91, $b = 42)
    ($a = 17, $b = 30)
    ($a = 85, $b = 63)

    where clause:

    where $a > $b

    Output tuple stream:

    ($a = 91, $b = 42)
    ($a = 85, $b = 63)
  • The following query illustrates how a where clause might be used with a positional variable to perform sampling on an input sequence. The query returns one value out of each one hundred input values.

                         for $x at $i in $input
    where $i mod 100 = 0
    return $x

4.13.6 While Clause

Changes in 4.0  

  1. A FLWOR expression may now include a while clause, which causes early exit from the iteration when a condition is encountered.   [Issue 187 PR 943 6 February 2024]

WhileClause::="while" ExprSingle

A while clause serves as a filter for the tuples in its input tuple stream. The expression in the while clause, called the while-expression, is evaluated once for each of these tuples. If the effective boolean value of the while-expression is true, the tuple is retained in the output tuple stream; otherwise the tuple and all subsequent tuples in the stream are discarded.

Examples:

  • This example illustrates the effect of a while clause on a tuple stream.

    Input tuple stream:

    ($a = 13, $b = 11)
    ($a = 91, $b = 42)
    ($a = 17, $b = 30)
    ($a = 85, $b = 63)

    while clause:

    while $a > $b

    Output tuple stream:

    ($a = 13, $b = 11)
    ($a = 91, $b = 42)
  • The following query illustrates how a while clause might be used to extract all items in an input sequence before the first one that fails to satisfy some condition. In this case it selects the leading para elements in the input sequence, stopping before the first element that is not a para element.

    for $x in $section/*
    while $x[self::para]
    return $x
  • The following query illustrates how a while clause might be used to limit the number of items returned in the query result.

    for $x in $section/para
    where contains($x, 'the')
    count $total
    while $total le 10
    return $x

    In this example a where clause would have exactly the same effect, but might require a smarter optimizer to deliver the same performance.

Note:

Although the semantics are described in terms of discarding all the tuples following the first one that fails to match the condition, a practical implementation is likely to avoid evaluating those tuples, thus giving an "early exit" from the iteration performed by the FLWOR expression.

Note:

The expression for $i in $input while $i le 3 differs from the expression subsequence-where($input, to := fn {. gt 3 }) in that the while expression drops the first item that is greater than 3, while the subsequence-where expression retains it.

Note:

The effect of the while clause is unpredictable in cases where the ordering of the tuple stream is unpredictable. This can happen, for example, when iterating over the entries in a map.

4.13.7 Count Clause

CountClause::="count" VarName

The purpose of a count clause is to enhance the tuple stream with a new variable that is bound, in each tuple, to the ordinal position of that tuple in the tuple stream. The name of the new variable is specified in the count clause. Its type is implicitly xs:integer.

The output tuple stream of a count clause is the same as its input tuple stream, with each tuple enhanced by one additional variable that is bound to the ordinal position of that tuple in the tuple stream. However, if the name of the new variable is the same as the name of an existing variable in the input tuple stream, the new variable occludes (replaces) the existing variable of the same name, and the number of bound variables in each tuple is unchanged.

The following examples illustrate uses of the count clause:

  • This example illustrates the effect of a count clause on an input tuple stream:

    Input tuple stream:

    ($name = "Bob", $age = 21)
    ($name = "Carol", $age = 19)
    ($name = "Ted", $age = 20)
    ($name = "Alice", $age = 22)

    count clause:

    count $counter

    Output tuple stream:

    ($name = "Bob", $age = 21, $counter = 1)
    ($name = "Carol", $age = 19, $counter = 2)
    ($name = "Ted", $age = 20, $counter = 3)
    ($name = "Alice", $age = 22, $counter = 4)
  • This example illustrates how a counter might be used to filter the result of a query. The query ranks products in order by decreasing sales, and returns the three products with the highest sales. Assume that the variable $products is bound to a sequence of product elements, each of which has name and sales child-elements.

    for $p in $products
    order by $p/sales descending
    count $rank
    while $rank <= 3
    return <product rank="{ $rank }">{ $p/name, $p/sales }</product>

    The result of this query has the following structure:

    <product rank="1">
      <name>Toaster</name>
      <sales>968</sales>
    </product>
    <product rank="2">
      <name>Blender</name>
      <sales>520</sales>
    </product>
    <product rank="3">
      <name>Can Opener</name>
      <sales>475</sales>
    </product>

4.13.8 Group By Clause

GroupByClause::="group" "by" (GroupingSpec ++ ",")
GroupingSpec::=VarName (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
VarNameAndType::="$" EQNameTypeDeclaration?

A group by clause generates an output tuple stream in which each tuple represents a group of tuples from the input tuple stream that have equivalent grouping keys. We will refer to the tuples in the input tuple stream as pre-grouping tuples, and the tuples in the output tuple stream as post-grouping tuples.

The group by clause assigns each pre-grouping tuple to a group, and generates one post-grouping tuple for each group. In the post-grouping tuple for a group, each grouping key is represented by a variable that was specified in a GroupingSpec, and every variable that appears in the pre-grouping tuples that were assigned to that group is represented by a variable of the same name, bound to a sequence of all values bound to the variable in any of these pre-grouping tuples. Subsequent clauses in the FLWOR expression see only the variable bindings in the post-grouping tuples; they no longer have access to the variable bindings in the pre-grouping tuples. The number of post-grouping tuples is less than or equal to the number of pre-grouping tuples.

A group by clause contains one or more grouping specifications, as shown in the grammar. [Definition: Each grouping specification specifies one grouping variable, which refers to variable bindings in the pre-grouping tuples. The values of the grouping variables are used to assign pre-grouping tuples to groups.] Each grouping specification may optionally provide an expression to which its grouping variable is bound. If no expression is provided, the grouping variable name must be equal (by the eq operator on expanded QNames) to the name of a variable in the input tuple stream, and it refers to that variable; otherwise a static error is raised [err:XQST0094]. For each grouping specification that contains a binding expression, a let binding is created in the pre-grouping tuples, and the grouping variable refers to that let binding. For example, the clause:

group by $g1, $g2 := $expr1, $g3 := $expr2 collation "Spanish"

is semantically equivalent to the following sequence of clauses:

let $g2 := $expr1
let $g3 := $expr2
group by $g1, $g2, $g3 collation "Spanish"

The process of group formation proceeds as follows:

  1. [Definition: The atomized value of a grouping variable is called a grouping key.] For each pre-grouping tuple, the grouping keys are created by atomizing the values of the grouping variables (in the post-grouping tuples, each grouping variable is set to the value of the corresponding grouping key, as discussed below). If the value of any grouping variable consists of more than one item, a type error is raised [err:XPTY0004]. If a type declaration is present and the resulting atomized value is not an instance of the specified type, a type error is raised [err:XPTY0004].

  2. The input tuple stream is partitioned into groups of tuples whose grouping keys are equivalent. [Definition: Two tuples T1 and T2 have equivalent grouping keys if and only if, for each grouping variable GV, the atomized value of GV in T1 is deep-equal to the atomized value of GV in T2, as defined by applying the function fn:deep-equal using the appropriate collation.]

    Note:

    The fn:deep-equal has been changed in XQuery 4.0 so that it is now transitive; the problem that existed in earlier versions when comparing numeric values of different types has thereby been resolved.

    Note:

    The atomized grouping key will always be either an empty sequence or a single atomic item. Defining equivalence by reference to the fn:deep-equal function ensures that the empty sequence is equivalent only to the empty sequence, that NaN is equivalent to NaN, that untypedAtomic items are compared as strings, and that values for which the eq operator is not defined are considered non-equivalent.

  3. The appropriate collation for comparing two grouping keys is the collation specified in the pertinent GroupingSpec if present, or the default collation from the dynamic context otherwise. If the collation is specified by a relative URI, that relative URI is resolved to an absolute URI using the Static Base URI. If the specified collation is not found in statically known collations, a static error is raised [err:XQST0076].

Each group of tuples produced by the above process results in one post-grouping tuple. The pre-grouping tuples from which the group is derived have equivalentgrouping keys, but these keys are not necessarily identical (for example, the strings "Frog" and "frog" might be equivalent according to the collation in use.) In the post-grouping tuple, each grouping variable is bound to the value of the corresponding grouping key.

In the post-grouping tuple generated for a given group, each non-grouping variable is bound to a sequence containing the concatenated values of that variable in all the pre-grouping tuples that were assigned to that group. The values derived from individual tuples are concatenated in a way that preserves the order of the pre-grouping tuple stream.

Note:

This behavior may be surprising to SQL programmers, since SQL reduces the equivalent of a non-grouping variable to one representative value. Consider the following query:

let $x := 64000
for $c in //customer
where $c/salary > $x
group by $d := $c/department
return <department name="{ $d }">
  Number of employees earning more than ${ $x } is { count($c) }
</department>

If there are three qualifying customers in the sales department this evaluates to:

<department name="sales">
  Number of employees earning more than $64000 64000 64000 is 3
</department>

In XQuery, each group is a sequence of items that match the group by criteria—in a tree-structured language like XQuery, this is convenient, because further structures can be built based on the items in this sequence. Because there are three items in the group, $x evaluates to a sequence of three items. To reduce this to one item, use fn:distinct-values():

let $x := 64000
for $c in //customer
let $d := $c/department
where $c/salary > $x
group by $d
return <department name="{ $d }">
  Number of employees earning more than ${ distinct-values($x) } is { count($c) }
</department>

Note:

In general, the static type of a variable in a post-grouping tuple is different from the static type of the variable with the same name in the pre-grouping tuples.

The order in which tuples appear in the post-grouping tuple stream is implementation-dependent.

Note:

An order by clause can be used to impose a value-based ordering on the post-grouping tuple stream. Similarly, if it is desired to impose a value-based ordering within a group (i.e., on the sequence of items bound to a non-grouping variable), this can be accomplished by a nested FLWOR expression that iterates over these items and applies an order by clause. In some cases, a value-based ordering within groups can be accomplished by applying an order by clause on a non-grouping variable before applying the group by clause.

A group by clause rebinds all the variables in the input tuple stream. The scopes of these variables are not affected by the group by clause, but in post-grouping tuples the values of the variables represent group properties rather than properties of individual pre-grouping tuples.

Examples:

  • This example illustrates the effect of a group by clause on a tuple stream.

    Input tuple stream:

    ($storeno = <storeno>S101</storeno>, $itemno = <itemno>P78395</itemno>)
    ($storeno = <storeno>S102</storeno>, $itemno = <itemno>P94738</itemno>)
    ($storeno = <storeno>S101</storeno>, $itemno = <itemno>P41653</itemno>)
    ($storeno = <storeno>S102</storeno>, $itemno = <itemno>P70421</itemno>)

    group by clause:

    group by $storeno

    Output tuple stream:

    ($storeno = S101, $itemno = (<itemno>P78395</itemno>, <itemno>P41653</itemno>))
    ($storeno = S102, $itemno = (<itemno>P94738</itemno>, <itemno>P70421</itemno>))
  • This example and the ones that follow are based on two separate sequences of elements, named $sales and $products. We assume that the variable $sales is bound to a sequence of elements with the following structure:

    <sales>
      <storeno>S101</storeno>
      <itemno>P78395</itemno>
      <qty>125</qty>
    </sales>

    We also assume that the variable $products is bound to a sequence of elements with the following structure:

    <product>
      <itemno>P78395</itemno>
      <price>25.00</price>
      <category>Men's Wear</category>
    </product>

    The simplest kind of grouping query has a single grouping variable. The query in this example finds the total quantity of items sold by each store:

    for $s in $sales
    let $storeno := $s/storeno
    group by $storeno
    return <store number="{ $storeno }" total-qty="{ sum($s/qty) }"/>

    The result of this query is a sequence of elements with the following structure:

    <store number="S101" total-qty="1550" />
    <store number="S102" total-qty="2125" />
  • In a more realistic example, a user might be interested in the total revenue generated by each store for each product category. Revenue depends on both the quantity sold of various items and the price of each item. The following query joins the two input sequences and groups the resulting tuples by two grouping variables:

    for $s in $sales
    for $p in $products[itemno = $s/itemno]
    let $revenue := $s/qty * $p/price
    group by $storeno := $s/storeno, 
             $category := $p/category
    return <summary storeno="{ $storeno }"
                    category="{ $category }"
                    revenue="{ sum($revenue) }"/>

    The result of this query is a sequence of elements with the following structure:

    <summary storeno="S101" category="Men's Wear" revenue="10185"/>
    <summary storeno="S101" category="Stationery" revenue="4520"/>
    <summary storeno="S102" category="Men's Wear" revenue="9750"/>
    <summary storeno="S102" category="Appliances" revenue="22650"/>
    <summary storeno="S102" category="Jewelry" revenue="30750"/>
  • The result of the previous example was a “flat” list of elements. A user might prefer the query result to be presented in the form of a hierarchical report, grouped primarily by store (in order by store number) and secondarily by product category. Within each store, the user might want to see only those product categories whose total revenue exceeds $10,000, presented in descending order by their total revenue. This report is generated by the following query:

    for $s1 in $sales
    let $storeno := $s1/storeno
    group by $storeno
    order by $storeno
    return <store storeno="{ $storeno }">{
      for $s2 in $s1
      for $p in $products[itemno = $s2/itemno]
      let $category := $p/category
      let $revenue := $s2/qty * $p/price
      group by $category
      let $group-revenue := sum($revenue)
      where $group-revenue > 10000
      order by $group-revenue descending
      return <category name="{ $category }" revenue="{ $group-revenue }"/>
    }</store>

    The result of this example query has the following structure:

    <store storeno="S101">
      <category name="Men's Wear" revenue="10185"/>
    </store>
    <store storeno="S102">
      <category name="Jewelry" revenue="30750"/>
      <category name="Appliances" revenue="22650"/>
    </store>
  • The following example illustrates how to avoid a possible pitfall in writing grouping queries.

    In each post-grouping tuple, all variables except for the grouping variable are bound to sequences of items derived from all the pre-grouping tuples from which the group was formed. For instance, in the following query, $high-price is bound to a sequence of items in the post-grouping tuple.

    let $high-price := 1000
    for $p in $products[price > $high-price]
    let $category := $p/category
    group by $category
    return <category name="{ $category }">{
      count($p) || ' products have price greater than ' || $high-price || '.'
    }</category>

    If three products in the “Men’s Wear” category have prices greater than 1000, the result of this query might look (in part) like this:

    <category name="Men’s Wear">
      3 products have price greater than 1000 1000 1000.
    </category>

    The repetition of "1000" in this query result is due to the fact that $high-price is not a grouping variable. One way to avoid this repetition is to move the binding of $high-price to an outer-level FLWOR expression, as follows:

    let $high-price := 1000
    return (
      for $p in $products[price > $high-price]
      let $category := $p/category
      group by $category
      return <category name="{ $category }">{
        count($p) || ' products have price greater than ' || $high-price || '.'
      }</category>  
    )

    The result of the revised query might contain the following element:

    <category name="Men's Wear">
      3 products have price greater than 1000.
    </category>

Note:

If a collation name is specified, it must be supplied as a literal string; it cannot be computed dynamically. A workaround in such cases is to use the fn:collation-key function. For example:

for $p in $products
group by collation-key($p/description, $collation)
return $product/@code

Note however that the fn:collation-key function might not work for all collations.

Note:

Grouping can also be achieved by constructing a map. For example, the function call map:build(//employee, fn{department}) constructs a map in which employees are grouped by department.

4.13.9 Order By Clause

OrderByClause::="stable"? "order" "by" OrderSpec ("," OrderSpec)*
OrderSpec::=ExprSingleOrderModifier
OrderModifier::=("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?

The purpose of an order by clause is to impose a value-based ordering on the tuples in the tuple stream. The output tuple stream of the order by clause contains the same tuples as its input tuple stream, but the tuples may be in a different order.

An order by clause contains one or more ordering specifications, called orderspecs, as shown in the grammar. For each tuple in the input tuple stream, the orderspecs are evaluated, using the variable bindings in that tuple. The relative order of two tuples is determined by comparing the values of their orderspecs, working from left to right until a pair of unequal values is encountered. If an orderspec specifies a collation, that collation is used in comparing values of type xs:string, xs:anyURI, or types derived from them (otherwise, the default collation is used in comparing values of these types). If an orderspec specifies a collation by a relative URI, that relative URI is resolved to an absolute URI using the Static Base URI. If an orderspec specifies a collation that is not found in statically known collations, an error is raised [err:XQST0076].

The process of evaluating and comparing the orderspecs is based on the following rules:

  • Atomization is applied to the result of the expression in each orderspec. If the result of atomization is neither a single atomic item nor an empty sequence, a type error is raised [err:XPTY0004].

For the purpose of determining their relative position in the ordering sequence, the greater-than relationship between two orderspec values W and V is defined as follows:

  • When the orderspec specifies empty least, the following rules are applied in order:

    1. If V is an empty sequence and W is not an empty sequence, then Wgreater-thanV is true.

    2. If V is NaN and W is neither NaN nor an empty sequence, then Wgreater-thanV is true.

    3. If V and W are both instances of xs:string, xs:anyURI, or xs:untypedAtomic, they are compared using the function fn:compare(V, W, C) where C is the requested collation, defaulting to the default collation from the static context.

      If fn:compare(V, W, C) is less than zero, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

    4. If V and W are both instances of xs:numeric, they are compared using the function fn:compare(V, W).

      If fn:compare(V, W) is less than zero, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

    5. If none of the above rules apply, then:

      If W gt V is true, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

  • When the orderspec specifies empty greatest, the following rules are applied in order:

    1. If W is an empty sequence and V is not an empty sequence, then Wgreater-thanV is true.

    2. If W is NaN and V is neither NaN nor an empty sequence, then Wgreater-thanV is true.

    3. If V and W are both instances of xs:string, xs:anyURI, or xs:untypedAtomic, they are compared using the function fn:compare(V, W, C) where C is the requested collation, defaulting to the default collation from the static context.

      If fn:compare(V, W, C) is less than zero, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

    4. If V and W are both instances of xs:numeric, they are compared using the function fn:compare(V, W).

      If fn:compare(V, W) is less than zero, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

    5. If none of the above rules apply, then:

      If W gt V is true, then Wgreater-thanV is true; otherwise Wgreater-thanV is false.

  • When the orderspec specifies neither empty least nor empty greatest, the default order for empty sequences in the static context determines whether the rules for empty least or empty greatest are used.

If T1 and T2 are two tuples in the input tuple stream, and V1 and V2 are the first pair of values encountered when evaluating their orderspecs from left to right for which one value is greater-than the other (as defined above), then:

  1. If V1 is greater-thanV2: If the orderspec specifies descending, then T1 precedes T2 in the output tuple stream; otherwise, T2 precedes T1 in the output tuple stream.

  2. If V2 is greater-thanV1: If the orderspec specifies descending, then T2 precedes T1 in the output tuple stream; otherwise, T1 precedes T2 in the output tuple stream.

If neither V1 nor V2 is greater-than the other for any pair of orderspecs for tuples T1 and T2, the following rules apply.

  1. If stable is specified, the original order of T1 and T2 is preserved in the output tuple stream.

  2. If stable is not specified, the order of T1 and T2 in the output tuple stream is implementation-dependent.

Note:

If two orderspecs return the special floating-point values positive and negative zero, neither of these values is greater-than the other, since +0.0 gt -0.0 and -0.0 gt +0.0 are both false.

Examples:

  • This example illustrates the effect of an order by clause on a tuple stream. The keyword stable indicates that, when two tuples have equal sort keys, their order in the input tuple stream is preserved.

    Input tuple stream:

    ($license = "PFQ519", $make = "Ford",  $value = 16500)
    ($license = "HAJ865", $make = "Honda", $value = 22750)
    ($license = "NKV473", $make = "Ford",  $value = 21650)
    ($license = "RCM922", $make = "Dodge", $value = 11400)
    ($license = "ZBX240", $make = "Ford",  $value = 16500)
    ($license = "KLM030", $make = "Dodge", $value = () )

    order by clause:

    stable order by $make,
      $value descending empty least

    Output tuple stream:

    ($license = "RCM922", $make = "Dodge", $value = 11400)
    ($license = "KLM030", $make = "Dodge", $value = () )
    ($license = "NKV473", $make = "Ford",  $value = 21650)
    ($license = "PFQ519", $make = "Ford",  $value = 16500)
    ($license = "ZBX240", $make = "Ford",  $value = 16500)
    ($license = "HAJ865", $make = "Honda", $value = 22750)
  • The following example shows how an order by clause can be used to sort the result of a query, even if the sort key is not included in the query result. This query returns employee names in descending order by salary, without returning the actual salaries:

    for $e in $employees
    order by $e/salary descending
    return $e/name

Note:

If a collation name is specified, it must be supplied as a literal string; it cannot be computed dynamically. Two possible workarounds are to use the fn:sort function or the fn:collation-key function.

Using fn:sort the expression

for $b in $books/book[price < 100]
order by $b/title
return $b

can be replaced with the following, which uses a dynamically-chosen collation:

sort(
  $books/book[price < 100],
  $collation,
  function($book) { $book/title }
)

Alternatively, it is possible to compute collation keys using a dynamically-chosen collation, and sort on the values of the collation keys:

for $b in $books/book[price < 100]
order by collation-key($b/title, $collation)
return $b

Note however that the fn:collation-key function might not work for all collations.

4.13.10 Return Clause

ReturnClause::="return" ExprSingle

The return clause is the final clause of a FLWOR expression. The return clause is evaluated once for each tuple in its input tuple stream, using the variable bindings in the respective tuples, in the order in which these tuples appear in the input tuple stream. The results of these evaluations are concatenated, as if by the comma operator, to form the result of the FLWOR expression.

The following example illustrates a FLWOR expression containing several clauses. The for clause iterates over all the departments in an input document named depts.xml, binding the variable $d to each department in turn. For each binding of $d, the let clause binds variable $e to all the employees in the given department, selected from another input document named emps.xml (the relationship between employees and departments is represented by matching their deptno values). Each tuple in the resulting tuple stream contains a pair of bindings for $d and $e ($d is bound to a department and $e is bound to a set of employees in that department). The where clause filters the tuple stream, retaining only those tuples that represent departments having at least ten employees. The order by clause orders the surviving tuples in descending order by the average salary of the employees in the department. The return clause constructs a new big-dept element for each surviving tuple, containing the department number, headcount, and average salary.

for $d in doc("depts.xml")//dept
let $e := doc("emps.xml")//emp[deptno eq $d/deptno]
where count($e) >= 10
order by avg($e/salary) descending
return <big-dept>{
  $d/deptno,
  <headcount>{ count($e) }</headcount>,
  <avgsal>{ avg($e/salary) }</avgsal>
}</big-dept>

Notes:

  • The order in which items appear in the result of a FLWOR expression depends on the ordering of the input tuple stream to the return clause, which in turn is influenced by order by clauses. For example, consider the following query, which is based on the same two input documents as the previous example:

    for $d in doc("depts.xml")//dept
    order by $d/deptno
    for $e in doc("emps.xml")//emp[deptno eq $d/deptno]
    return <assignment>{
      $d/deptno, $e/name
    }</assignment>

    The result of this query is a sequence of assignment elements, each containing a deptno element and a name element. The sequence will be ordered primarily by the deptno values because of the order by clause. Subsequences of assignment elements with equal deptno values will be ordered by the document order of their name elements within the emps.xml document.

  • Parentheses are helpful in return clauses that contain comma operators, since FLWOR expressions have a higher precedence than the comma operator. For example, the following query raises an error because after the comma, $j is no longer within the FLWOR expression, and is an undefined variable:

    let $i := 5
    let $j := 20 * $i
    return $i, $j

    Parentheses can be used to bring $j into the return clause of the FLWOR expression, as the programmer probably intended:

    let $i := 5
    let $j := 20 * $i
    return ($i, $j)

4.14 Maps and Arrays

Most modern programming languages have support for collections of key/value pairs, which may be called maps, dictionaries, associative arrays, hash tables, keyed lists, or objects (these are not the same thing as objects in object-oriented systems). In XQuery 4.0, we call these maps. Most modern programming languages also support ordered lists of values, which may be called arrays, vectors, or sequences. In XQuery 4.0, we have both sequences and arrays. Unlike sequences, an array is an item, and can appear as an item in a sequence.

Note:

The XQuery 4.0 specification focuses on syntax provided for maps and arrays, especially constructors and lookup.

Some of the functionality typically needed for maps and arrays is provided by functions defined in Section 17 MapsFO and Section 18 ArraysFO, including functions used to read JSON to create maps and arrays, serialize maps and arrays to JSON, combine maps to create a new map, remove map entries to create a new map, iterate over the keys of a map, convert an array to create a sequence, combine arrays to form a new array, and iterate over arrays in various ways.

4.14.1 Maps

[Definition: A map is a function that associates a set of keys with values, resulting in a collection of key / value pairs.] [Definition: Each key / value pair in a map is called an entry.] [Definition: The value associated with a given key is called the associated value of the key.]

4.14.1.1 Map Constructors

Changes in 4.0  

  1. In map constructors, the keyword map is now optional, so map { 0: false(), 1: true() } can now be written { 0: false(), 1: true() }, provided it is used in a context where this creates no ambiguity.   [Issue 1070 PR 1071 26 March 2024]

A map can be created using a MapConstructor.

MapConstructor::="map"? "{" (MapConstructorEntry ** ",") "}"
MapConstructorEntry::=MapKeyExpr ":" MapValueExpr
MapKeyExpr::=ExprSingle
MapValueExpr::=ExprSingle

Note:

The keyword map was required in earlier versions of the language; in XQuery 4.0 it becomes optional. There may be cases where using the keyword improves readability.

In order to allow the map keyword to be omitted, an incompatible change has been made to XQuery computed element and attribute constructors: if the name of the constructed element or attribute is a language keyword, it must now be written in quotes, for example element "div" {}.

Although the grammar allows a MapConstructor to appear within an EnclosedExpr (that is, between curly brackets), this may be confusing to readers, and using the map keyword in such cases may improve clarity. In any event, if the EnclosedExpr appears in a context such as a StringTemplate, the two adjacent left opening braces must at least be separated by whitespace.

Note:

In some circumstances, it is necessary to include whitespace before or after the colon of a MapConstructorEntry to ensure that it is parsed as intended.

For instance, consider the expression {a:b}. Although it matches the EBNF for MapConstructor (with a matching MapKeyExpr and b matching MapValueExpr), the "longest possible match" rule requires that a:b be parsed as a QName, which results in a syntax error. Changing the expression to {a :b} or {a: b} will prevent this, resulting in the intended parse.

Similarly, consider these three expressions:

{a:b:c}
{a:*:c}
{*:b:c}

In each case, the expression matches the EBNF in two different ways, but the “longest possible match” rule forces the parse in which the MapKeyExpr is a:b, a:*, or *:b (respectively) and the MapValueExpr is c. To achieve the alternative parse (in which the MapKeyExpr is merely a or *), insert whitespace before and/or after the first colon.

See A.3 Lexical structure.

The value of the expression (whether or not the map keyword is present) is a map whose entries correspond to the key-value pairs obtained by evaluating the successive MapKeyExpr and MapValueExpr expressions.

Each MapKeyExpr expression is evaluated and atomized; a type error [err:XPTY0004] occurs if the result is not a single atomic item. The associated value is the result of evaluating the corresponding MapValueExpr. If the MapValueExpr evaluates to a node, the associated value is the node itself, not a new node with the same values. [Definition: Two atomic items K1 and K2 have the same key value if fn:atomic-equal(K1, K2) returns true, as specified in Section 13.2.1 fn:atomic-equalFO ] If two or more entries have the same key value then a dynamic error is raised [err:XQDY0137]. The error may be raised statically if two or more entries can be determined statically to have the same key value.

Example: Constructing a fixed map

The following expression constructs a map with seven entries:

{
  "Su" : "Sunday",
  "Mo" : "Monday",
  "Tu" : "Tuesday",
  "We" : "Wednesday",
  "Th" : "Thursday",
  "Fr" : "Friday",
  "Sa" : "Saturday"
}

 

Example: Constructing nested maps

Maps can nest, and can contain any XDM value. Here is an example of a nested map with values that can be string values, numeric values, or arrays:

{
  "book": {
    "title": "Data on the Web",
    "year": 2000,
    "author": [
      {
        "last": "Abiteboul",
        "first": "Serge"
      },
      {
        "last": "Buneman",
        "first": "Peter"
      },
      {
        "last": "Suciu",
        "first": "Dan"
      }
    ],
    "publisher": "Morgan Kaufmann Publishers",
    "price": 39.95
  }
}

Note:

The syntax deliberately mimics JSON, but there are a few differences. JSON constructs that are not accepted in XQuery 4.0 map constructors include the keywords true, false, and null, and backslash-escaped characters such as "\n" in string literals. In an XQuery 4.0 map constructor, of course, any literal value can be replaced with an expression.

Both the keys and the values in a map constructor can be supplied as expressions rather than as constants; the number of entries in the map, however, is fixed. There are several functions that can be used to construct maps with a variable number of entries:

  • map:build takes any sequence as input, and for each item in the sequence, it computes a key and a value, by calling user-supplied functions.

  • map:merge takes a sequence of maps (often but not necessarily single-entry maps) and merges them into a single map.

  • map:of-pairs takes a sequence of key-value pair mapsFO and merges them into a single map.

Any of these functions can be used to build an index of employee elements using the value of the @id attribute as a key:

  • map:build(//employee, fn{@id})

  • map:merge(//employee ! {@id, .})

  • map:of-pairs(//employee ! {'key':@id, 'value':.})

All three functions also provide control over how duplicate keys are handled, allowing them to be used to create a map in which items are grouped according to the value of a grouping key.

4.14.1.2 Maps as Functions

Maps are function items, and a dynamic function call can be used to look up the value associated with a key in a map. If $map is a map and $key is a key, then $map($key) is equivalent to map:get($map, $key). The semantics of such a function call are formally defined in Section 17.3.9 map:getFO.

Examples:

Note:

XQuery 4.0 also provides an alternate syntax for map and array lookup that is more terse, supports wildcards, and allows lookup to iterate over a sequence of maps or arrays. See 4.14.3 Lookup Expressions for details.

Map lookups can be chained.

Examples: (These examples assume that $b is bound to the books map from the previous section)

  • The expression $b("book")("title") returns the string Data on the Web.

  • The expression $b("book")("author") returns the array of authors.

  • The expression $b("book")("author")(1)("last") returns the string Abiteboul.

    (This example combines 4.14.2.2 Arrays as Functions with map lookups.)

4.14.2 Arrays

4.14.2.1 Array Constructors

[Definition: An array is a function item that associates a set of positions, represented as positive integer keys, with values.] The first position in an array is associated with the integer 1. [Definition: The values of an array are called its members.] In the type hierarchy, array has a distinct type, which is derived from function. Atomization converts arrays to sequences (see Atomization).

An array is created using an ArrayConstructor.

ArrayConstructor::=SquareArrayConstructor | CurlyArrayConstructor
SquareArrayConstructor::="[" (ExprSingle ** ",") "]"
CurlyArrayConstructor::="array" EnclosedExpr

If a member of an array is a node, its node identity is preserved. In both forms of an ArrayConstructor, if a member expression evaluates to a node, the associated value is the node itself, not a new node with the same values. If the member expression evaluates to a map or array, the associated value is a new map or array with the same values.

A SquareArrayConstructor consists of a comma-delimited set of argument expressions. It returns an array in which each member contains the value of the corresponding argument expression.

Examples:

  • [ 1, 2, 5, 7 ] creates an array with four members: 1, 2, 5, and 7.

  • [ (), (27, 17, 0) ] creates an array with two members: () and the sequence (27, 17, 0).

  • [ $x, local:items(), <tautology>It is what it is.</tautology> ] creates an array with three members: the value of $x, the result of evaluating the function call, and a tautology element.

A CurlyArrayConstructor can use any expression to create its members. It evaluates its operand expression to obtain a sequence of items and creates an array with these items as members. Unlike a SquareArrayConstructor, a comma in a CurlyArrayConstructor is the comma operator, not a delimiter.

Examples:

  • array { $x } creates an array with one member for each item in the sequence to which $x is bound.

  • array { local:items() } creates an array with one member for each item in the sequence to which local:items() evaluates.

  • array { 1, 2, 5, 7 } creates an array with four members: 1, 2, 5, and 7.

  • array { (), (27, 17, 0) } creates an array with three members: 27, 17, and 0.

  • array { $x, local:items(), <tautology>It is what it is.</tautology> } creates an array with the following members: the items to which $x is bound, followed by the items to which local:items() evaluates, followed by a tautology element.

Note:

XQuery 4.0 does not provide explicit support for sparse arrays. Use integer-valued maps to represent sparse arrays, for example: { 27 : -1, 153 : 17 }.

4.14.2.2 Arrays as Functions

Arrays are function items, and a dynamic function call can be used to look up the value associated with position in an array. If $array is an array and $index is an integer corresponding to a position in the array, then $array($key) is equivalent to array:get($array, $key). The semantics of such a function call are formally defined in Section 18.2.11 array:getFO.

Examples:

  • [ 1, 2, 5, 7 ](4) evaluates to 7.

  • [ [ 1, 2, 3 ], [ 4, 5, 6 ] ](2) evaluates to [ 4, 5, 6 ].

  • [ [ 1, 2, 3 ], [ 4, 5, 6 ] ](2)(2) evaluates to 5.

  • [ 'a', 123, <name>Robert Johnson</name> ](3) evaluates to <name>Robert Johnson</name>.

  • array { (), (27, 17, 0) }(1) evaluates to 27.

  • array { (), (27, 17, 0) }(2) evaluates to 17.

  • array { "licorice", "ginger" }(20) raises a dynamic error [err:FOAY0001]FO40.

Note:

XQuery 4.0 also provides an alternate syntax for map and array lookup that is more terse, supports wildcards, and allows lookup to iterate over a sequence of maps or arrays. See 4.14.3 Lookup Expressions for details.

4.14.3 Lookup Expressions

Changes in 4.0  

  1. The lookup operator ? can now be followed by a string literal, for cases where map keys are strings other than NCNames. It can also be followed by a variable reference.

  2. A deep lookup operator ?? is provided for searching trees of maps and arrays.   [Issue 297 PR 837 23 November 2023]

  3. Lookup expressions can now take a modifier (such as keys, values, or pairs) enabling them to return structured results rather than a flattened sequence.   [Issues 960 1094 PR 1125 23 April 2024]

XQuery 4.0 provides two lookup operators ? and ?? for maps and arrays. These provide a terse syntax for accessing the entries in a map or the members of an array.

The operator "?", known as the shallow lookup operator, returns values found immediately in the operand map or array. The operator "??", known as the deep lookup operator, also searches nested maps and arrays. The effect of the deep lookup operator "??" is explained in 4.14.3.3 Deep Lookup.

4.14.3.1 Postfix Lookup Expressions
LookupExpr::=PostfixExprLookup
Lookup::=("?" | "??") (Modifier "::")? KeySpecifier
Modifier::="pairs" | "keys" | "values" | "items"
KeySpecifier::=NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | LookupWildcard
LookupWildcard::="*"

A Lookup has two parts: the KeySpecifier determines which entries (in a map) or members (in an array) are selected, and the Modifier determines how they are delivered in the result. The default modifier is items, which delivers the result as a flattened sequence of items.

To take a simple example, given $A as an array [ ("a", "b"), ("c", "d"), ("e", "f") ], some example Lookup expressions are:

Example Lookup Expressions on an Array
ExpressionResult
$A?* (or $A?items::*)
("a", "b", "c", "d", "e", "f")
$A?pairs::*
({ "key": 1, "value": ("a", "b") }, 
 { "key": 2, "value": ("c", "d") }, 
 { "key": 3, "value": ("e", "f") })
$A?values::*
([ "a", "b" ], [ "c", "d" ], [ "e", "f" ])
$A?keys::*
(1, 2, 3)
$A?2 (or $A?items::2)
("c", "d")
$A?pairs::2
({ "key": 2, "value":("c", "d") })
$A?values::2
([ "c", "d" ])
$A?keys::2
(2)
$A?(3, 1) (or $A?items::(3, 1))
("e", "f", "a", "b")
$A?pairs::(3, 1)
({ "key": 3, "value": ("e", "f") }, 
 { "key": 1, "value": ("a", "b") })
$A?values::(3, 1)
([ "e", "f" ][ "a", "b" ])
$A?keys::(3, 1)
(3, 1)

Similarly, given $M as a map { "X": ("a", "b"), "Y": ("c", "d"), "Z": ("e", "f") }, some example lookup expressions are as follows. Note that because maps are unordered, the results are not necessarily in the order shown.

Example Lookup Expressions on a Map
ExpressionResult
$M?* (or $M?items::*)
("a", "b", "c", "d", "e", "f")
$M?pairs::*
({ "key": "X", "value": ("a", "b") }, 
 { "key": "Y", "value": ("c", "d") }, 
 { "key": "Z", "value": ("e", "f") })
$M?values::*
([ "a", "b" ], [ "c", "d" ], [ "e", "f" ])
$M?keys::*
("X", "Y", "Z")
$M?Y (or $M?items::Y)
("c", "d")
$M?pairs::Y
({ "key": "Y", "value":("c", "d") })
$M?values::Y
([ "c", "d" ])
$M?keys::Y
("Y")
$M?("Z", "X") (or $A?items::("Z", "X"))
("e", "f", "a", "b")
$M?pairs::("Z", "X")
({ "key": "Z", "value": ("e", "f") }, 
 { "key": "X", "value": ("a", "b") })
$M?values::("Z", "X")
([ "e", "f" ][ "a", "b" ])
$M?keys::("Z", "X")
("Z", "X")

The semantics of a postfix lookup expression E?pairs::KS are defined as follows. The results with other modifiers can be derived from this result, as explained below.

  1. E is evaluated to produce a value $V.

  2. If $V is not a singleton (that is if count($V) ne 1), then the result (by recursive application of these rules) is the value of for $v in $V return $v?pairs::KS.

  3. If $V is a singleton array (that is, if $V instance of array(*)) then:

    1. If KS is a ParenthesizedExpr, then it is evaluated to produce a value $K and the result is:

      data($K) ! { "key": ., "value": array:get($V, .) }

      Note:

      The focus for evaluating the key specifier expression is the same as the focus for the Lookup expression itself.

    2. If the KeySpecifier is an IntegerLiteral with value $i, the result is the same as $V?pairs::($i).

    3. If the KeySpecifier is an NCNameor StringLiteral, the expression raises a type error [err:XPTY0004].

    4. If KS is a wildcard (*), the result is the same as $V?pairs::(1 to array:size($V)):

      Note:

      Note that array items are returned in order.

  4. If $V is a singleton map (that is, if $V instance of map(*)) then:

    1. If KS is a ParenthesizedExpr, then it is evaluated to produce a value $K and the result is:

      data($K) ! { "key": ., "value": map:get($V, .) }

      Note:

      The focus for evaluating the key specifier expression is the same as the focus for the Lookup expression itself.

    2. If KS is an NCName or a StringLiteral, with value $S, the result is the same as $V?pairs::($S)

    3. If KS is an IntegerLiteral with value $N, the result is the same as $V?pairs::($N).

    4. If KS is a wildcard (*), the result is the same as $V?pairs::(map:keys($V)).

      Note:

      The order of entries in the result sequence in this case is implementation-dependent.

  5. Otherwise (that is, if $V is neither a map nor an array) a type error is raised [err:XPTY0004].

If the modifier is items (explicitly or by default), the result of $V?items::KS is the same as the result of $V?pairs::KS ! map:get(., "value"); that is, it is the sequence concatenation of the value parts.

If the modifier is values, the result of $V?values::KS is the same as the result of $V?pairs::KS ! array { map:get(., "value") }.

If the modifier is keys, the result of $V?keys::KS is the same as the result of $V?pairs::KS ! map:get(., "key").

Examples:

  • { "first" : "Jenna", "last" : "Scott" }?first evaluates to "Jenna"

  • { "first name" : "Jenna", "last name" : "Scott" }?"first name" evaluates to "Jenna"

  • [ 4, 5, 6 ]?2 evaluates to 5.

  • ({ "first": "Tom" }, { "first": "Dick" }, { "first": "Harry" })?first evaluates to the sequence ("Tom", "Dick", "Harry").

  • ([ 1, 2, 3 ], [ 4, 5, 6 ])?2 evaluates to the sequence (2, 5).

  • ([ 1, [ "a", "b" ], [ 4, 5, [ "c", "d"] ])?value::*[. instance of array(xs:string)] evaluates to the sequence ([ "a", "b" ], [ "c", "d" ]).

  • [ "a", "b" ]?3 raises a dynamic error [err:FOAY0001]FO40

4.14.3.2 Unary Lookup
UnaryLookup::=("?" | "??") (Modifier "::")? KeySpecifier
Modifier::="pairs" | "keys" | "values" | "items"
KeySpecifier::=NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | LookupWildcard
LookupWildcard::="*"

Unary lookup is most commonly used in predicates (for example, $map[?name = 'Mike']) or with the simple map operator (for example, avg($maps ! (?price - ?discount))).

The unary lookup expression ?modifier::KS is defined to be equivalent to the postfix lookup expression .?modifier::KS which has the context value (.) as the implicit first operand. See 4.14.3.1 Postfix Lookup Expressions for the postfix lookup operator.

Examples:

  • ?name is equivalent to .("name"), an appropriate lookup for a map.

  • ?2 is equivalent to .(2), an appropriate lookup for an array or an integer-valued map.

  • If the context item is the result of parsing the JSON input:

    {
      "name": "John Smith",
      "address": { "street": "18 Acacia Avenue", "postcode": "MK12 2EX" },
      "previous-address": { "street": "12 Seaview Road", "postcode": "EX8 9AA" }
    }

    then ?*[. instance of record(street, postcode)]?postcode returns ("MK12 2EX", "EX8 9AA") (or some permutation thereof).

    Note:

    Writing ?*?postcode would raise a type error, because the result of the initial step ?* includes an item (the string "John Smith") that is neither a map nor an array.

  • ?"first name" is equivalent to .("first name")

  • ?("$funky / <looking @string") is equivalent to .("$funky / <looking @string"), an appropriate lookup for a map with rather odd conventions for keys.

  • ?($a)and ?$a are equivalent to for $k in $a return .($k), allowing keys for an array or map to be passed using a variable.

  • ?(2 to 4) is equivalent to for $k in (2, 3, 4) return .($k), a convenient way to return a range of values from an array.

  • ?(3.5) raises a type error if the context value is an array because the parameter must be an integer.

  • If the context value is an array, let $x:= <node i="3"/> return ?($x/@i) does not raise a type error because the attribute is untyped.

    But let $x:= <node i="3"/> return ?($x/@i+1) does raise a type error because the + operator with an untyped operand returns a double.

  • ([ 1, 2, 3 ], [ 1, 2, 5 ], [ 1, 2 ])[?3 = 5] raises an error because ?3 on one of the items in the sequence fails.

  • If $m is bound to the weekdays map described in 4.14.1 Maps, then $m?* returns the values ("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"), in implementation-dependent order.

  • [ 1, 2, 5, 7 ]?* evaluates to (1, 2, 5, 7).

  • [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]?* evaluates to ([ 1, 2, 3 ], [ 4, 5, 6 ])

  • [ [1, 2, 3], 4, 5 ]?*[. instance of array(xs:integer)] evaluates to ([1, 2, 3])

  • [ [ 1, 2, 3 ], [ 4, 5, 6 ], 7 ]?*[. instance of array(*)]?2 evaluates to (2, 5)

  • [ [ 1, 2, 3 ], 4, 5 ]?*[. instance of xs:integer] evaluates to (4, 5).

4.14.3.3 Deep Lookup

The deep lookup operator ?? has both unary and postfix forms. The unary form ??modifier::KS (where KS is any KeySpecifier) has the same effect as the binary form .??modifier::KS.

The semantics are defined as follows.

First we define the recursive content of an item as follows:

declare function immediate-content($item as item()) as record(key, value)* {
  if ($item instance of map(*)) {
    map:pairs($item)
  } else if ($item instance of array(*)) {
    for member $m at $p in $item
    return { "key": $p, "value": $m }
  }
};    

declare function recursive-content($item as item()) as record(key, value)* {
  immediate-content($item) ! (., ?items::value =!> recursive-content())
};

Note:

Explanation: the immediate content of a map is obtained by splitting it into a sequence of key-value pairs, each representing one entry. The immediate content of an array is obtained by constructing a sequence of key-value pairs, one for each array member, where the key is the array index and the value is the corresponding member. Each key-value pair is of type record(key as xs:anyAtomicType, value as item()*). The recursive content of an item contains the key-value pairs in its immediate content, each followed by the recursive content obtained by expanding any maps or arrays in the immediate content.

It is then useful to represent the recursive content as a sequence of singleton maps: so each pair { "key": $K, "value": $V } is converted to the form { $K: $V }. This can be achieved using the expression recursive-content($V) ! { ?key: ?value }.

In addition we define the function array-or-map as follows:

declare function array-or-map($item as item()) {
  typeswitch ($item) {
    case array(*) | map(*) return $item
    default return error(xs:QName("err:XPTY0004"))
  }
}

The result of the expression E??pairs::KS, where E is any expression and KS is any KeySpecifier, is then:

(
  (E =!> array-or-map() => recursive-content()) 
  ! { ?key: ?value }
) ? pairs::KS.

Note:

This is best explained by considering examples.

Consider the expression let $V := [ { "first": "John", "last": "Smith" }, { "first": "Mary", "last": "Evans" } ].

The recursive content of this array is the sequence of six maps:

  1. { "key": 1, "value": { "first": "John", "last": "Smith" } }

  2. { "key": 2, "value": { "first": "Mary", "last": "Evans" } }

  3. { "key": "first", "value": "John" }

  4. { "key": "last", "value": "Smith" }

  5. { "key": "first", "value": "Mary" }

  6. { "key": "last", "value": "Evans" }

The expression $V??pairs::* returns this sequence.

With some other KeySpecifierKS, $V??pairs::KS returns selected items from this sequence that match KS. Formally this is achieved by converting the key-value pairs to singleton maps, applying the KeySpecifier to the sequence of singleton maps, and then converting the result back into a sequence of key-value pairs.

For example, given the expression $V??pairs::first, the selection from the converted sequence will include the two singleton maps { "first" : "John" } and { "first" : "Mary" }, which will be delivered in key-value pair form as { "key": "first", "value": "John" }, { "key": "first", "value": "Mary" }.

The effect of using modifiers other than pairs is the same as with shallow lookup expressions:

  • If the modifier is items (explicitly or by default), the result of $V??items::KS is the same as the result of $V??pairs::KS ! map:get(., "value"); that is, it is the sequence concatenation of the value parts.

  • If the modifier is values, the result of $V??values::KS is the same as the result of $V??pairs::KS ! array { map:get(., "value") }.

  • If the modifier is keys, the result of $V??keys::KS is the same as the result of $V??pairs::KS ! map:get(., "key").

Note:

This means that with the example given earlier:

  • The expression $V ?? first returns the sequence "John", "Mary".

  • The expression $V ?? last returns the sequence "Smith", "Evans".

  • The expression $V ?? 1 returns the sequence { "first": "John", "last": "Smith" }.

  • The expression $V ?? *[. instance of record(first, last)] ! `{ ?first } { ?last }` returns the sequence "John Smith", "Mary Evans".

Note:

The effect of evaluating all shallow lookups on maps rather than arrays is that no error arises if an array subscript is out of bounds. In the above example, $value??3 would return an empty sequence, it would not raise an error.

This also affects the way an xs:untypedAtomic key value is handled. Given the shallow lookup expression $A?$x, if $A is an array and $x (after atomization) is xs:untypedAtomic then the value of $x is converted to an integer (by virtue of the coercion rules applying to a call on array:get). With a deep lookup expression $A??$x, by contrast, the semantics are defined in terms of a map lookup, in which xs:untypedAtomic items are always treated as strings.

Note:

The definition of the recursive-content function is such that items in the top-level value that are not maps or arrays are ignored, whereas items that are not themselves maps or arrays, but which appear in the content of a map or array at the top level, are included. This means that E??X mirrors the behavior of E//X, in that it includes all items that are one-or-more levels deep in the tree.

Note:

The result of the deep lookup operator retains order when processing sequences and arrays, but not when processing maps.

Note:

An expression involving multiple deep lookup operators may return duplicates. For example, the result of the expression [ [ [ "a" ], [ "b" ] ], [ [ "c" ], [ "d" ] ] ] ?? 1 ?? 1 is ([ "a" ], "a", "b", "a", "c"). This is because the first ?? operator selects members in position 1 at all three levels, that is it selects the arrays [ [ "a" ], [ "b" ] ], [ "a" ], and [ "c" ] as well as each of the four string values. The second ?? operator selects members in position 1 within each of these values, which results in the string "a" being selected twice.

Note:

A type error is raised if the value of the left-hand expression includes an item that is neither a map nor an array.

Example: Examples of Deep Lookup Expressions

Consider the tree $tree of maps and arrays that results from applying the fn:parse-json function to the following input:

{
  "desc"    : "Distances between several cities, in kilometers.",
  "updated" : "2014-02-04T18:50:45",
  "uptodate": true,
  "author"  : null,
  "cities"  : {
    "Brussels": [
      { "to": "London",    "distance": 322 },
      { "to": "Paris",     "distance": 265 },
      { "to": "Amsterdam", "distance": 173 }
    ],
    "London": [
      { "to": "Brussels",  "distance": 322 },
      { "to": "Paris",     "distance": 344 },
      { "to": "Amsterdam", "distance": 358 }
    ],
    "Paris": [
      { "to": "Brussels",  "distance": 265 },
      { "to": "London",    "distance": 344 },
      { "to": "Amsterdam", "distance": 431 }
     ],
    "Amsterdam": [
      { "to": "Brussels",  "distance": 173 },
      { "to": "London",    "distance": 358 },
      { "to": "Paris",     "distance": 431 }
    ]
  }
}

Given two variables $from and $to containing the names of two cities that are present in this table, the distance between the two cities can be obtained with the expression:

$tree ?? $from ?? *[. instance of record(to, distance)][?to = $to] ? distance

The names of all pairs of cities whose distance is represented in the data can be obtained with the expression:

$tree ?? $cities
=> map:for-each(fn($key, $val) { $val ?? to ! ($key || "-" || .) })

 

Example: Comparison with JSONPath

This example provides XPath equivalents to some examples given in the JSONPath specification. [TODO: add a reference].

The examples query the result of parsing the following JSON value, representing a store whose stock consists of four books and a bicycle:

{
  "store": {
    "book": [
      {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      {
        "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      {
        "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 399
    }
  }
}

The following table illustrates some queries on this data, expressed both in JSONPath and in XQuery 4.0.

JSONPath vs XQuery 4.0 Comparison
QueryJSONPathXQuery 4.0
The authors of all books in the store$.store.book[*].author$m?store?book??author
All authors$..author$m??author
All things in store (four books and a red bicycle)$.store.* $m?store?*
The prices of everything in the store$.store..price$m?store??price
The third book$..book[2] $m??book?3
The third book's author$..book[2].author$m??book?3?author
The third book's publisher (empty result)$..book[2].publisher$m??book?3?publisher
The last book (in order)$..book[-1]$m??book => array:foot()
The first two books$..book[0,1]$m??book?(1, 2)
All books with an ISBN$..book[?@.isbn]$m??book[?isbn]
All books cheaper than 10$..book[?@.price<10]$m??book[?price lt 10]
All member values and array elements contained in the input value$..*$m??*
4.14.3.4 Implausible Lookup Expressions

Under certain conditions a lookup expression that will never select anything is classified as implausible. During the static analysis phase, a processor may (subject to the rules in 2.4.6 Implausible Expressions) report a static error when such lookup expressions are encountered: [err:XPTY0145].

More specifically, a shallow unary or postfix lookup is classified as implausible if any of the following conditions applies:

  1. The inferred type of the left-hand operand (or the context value, in the case of a unary expression) is a record type (see 3.2.8.3 Record Type), and the KeySpecifier is an IntegerLiteral.

  2. The inferred type of the left-hand operand (or the context value, in the case of a unary expression) is a record type (see 3.2.8.3 Record Type), and the KeySpecifier is an NCName or StringLiteral that cannot validly appear as a field name in the record.

  3. The inferred type of the left-hand operand (or the context value, in the case of a unary expression) is a map type, and the inferred type of the KeySpecifier, after coercion, is a type that is disjoint with the key type of the map.

  4. The inferred type of the left-hand operand (or the context value, in the case of a unary expression) is an array type, and the KeySpecifier is the IntegerLiteral0 (zero).

Note:

Other errors, such as using an NCNameKeySpecifier for an array lookup, are handled under the general provisions for type errors.

Examples of implausible lookup expressions include the following:

  • parse-uri($uri)?3: the declared result type of parse-uri is a record test, so the selector 3 will never select anything.

  • in-scope-namespaces($node)(current-date()): the result type of in-scope-namespaces is a map with xs:string keys, so the selector current-date() will never select anything.

  • array:subarray($a, 2, 5)?0: the integer zero cannot select any member of an array, because numbering starts at 1.

4.14.4 Filter Expressions for Maps and Arrays

Changes in 4.0  

  1. Filter expressions for maps and arrays are introduced.   [Issue 1159 PR 1163 20 April 2024]

  2. Predicates in filter expressions for maps and arrays can now be numeric.   [Issue 1207 PR tba 15 May 2024]

FilterExprAM::=PostfixExpr "?[" Expr "]"

Maps and arrays can be filtered using the construct INPUT?[FILTER]. For example, $array?[count(.)=1] filters an array to retain only those members that are single items.

Note:

The character-pair ?[ forms a single token; no intervening whitespace or comment is allowed.

The required type of the left-hand operand INPUT is (map(*)|array(*))?: that is, it must be either an empty sequence, a single map, or a single array [err:XPTY0004]. If it is an empty sequence, the result of the expression is an empty sequence.

If the value of INPUT is an array, then the FILTER expression is evaluated for each member of the array, with that member as the context value, with its position in the array as the context position, and with the size of the array as the context size. The result of the expression is an array containing those members of the input array for which the predicate truth value of the FILTER expression is true. The order of retained members is preserved.

For example, the following expression:

let $array := [ (), 1, (2, 3), (4, 5, 6) ]
return $array?[count(.) ge 2]

returns:

[ (2, 3), (4, 5, 6) ]

Note:

Numeric predicates are handled in the same way as with filter expressions for sequences. However, the result is always an array, even if only one member is selected. For example, given the $array shown above, the result of $array?[3] is the singleton array [ (2, 3) ]. Contrast this with $array?3 which delivers the sequence 2, 3.

If the value of INPUT is a map, then the FILTER expression is evaluated for each entry in the map, with the context value set to an item of type record(key as xs:anyAtomicType, value as item()*), in which the key and value fields represent the key and value of the map entry. The context position is the position of the entry in the map (in an arbitrary ordering), and the context size is the number of entries in the map. The result of the expression is a map containing those entries of the input map for which the predicate truth value of the FILTER expression is true.

For example, the following expression:

let map := { 1: "alpha", 2: "beta", 3: "gamma" }
return $map?[?key ge 2]

returns:

{ 2: "beta", 3: "gamma" }

Note:

Filtering of maps based on numeric positions is not generally useful, because the order of entries in a map is unpredictable; but it is available in the interests of orthogonality.

4.14.5 Pinned Maps and Arrays

Unlike navigation within node trees derived from XML, navigation within a tree of maps and arrays derived from JSON is normally “downwards only”: there is no equivalent of the parent or ancestor axis. This means, for example, that having selected leav nodes in the tree with an expression such as ??name, there is no way of navigating from the items in the result to any related items. Pinned maps and arrays provide a solution to this problem; if a map or array is pinned (by calling the fn:pin function), then values found by navigating within the map or array are labeled, which provides supplementary information about their location within the containing tree structure.

For further information about pinned and labeled values see Section 2.10 Labeled ItemsDM.

More specifically, if a map $M or an array $A is pinned, then any value returned by map:get($M, $key) or array:get($A, $index) will be a sequence of labeled items. The label can be obtained by calling the function fn:label, and the result will be a map having the following properties:

  • pinned: set to true. This means that any further selections from this value (if it is itself a map or array) will also deliver labeled items.

  • parent: the containing map ($M) or array ($A).

  • key: the key ($key) or index ($index) that was used to select the item.

  • position: in the general case the value returned by map:get or array:get is a sequence, and each item in the sequence is labeled with its 1-based position in that sequence.

  • ancestors: a zero-arity function that delivers the item's parent (its containing map or array), that item's parent, and so on, recursively, up to the map or array that was the root of the selection. The sequence is in upwards navigation order (the immediate parent comes first).

  • path: a zero-arity function that delivers the sequence of keys (in the case of maps) or integer indexes (in the case of arrays) by which the item was reached. The sequence is in downwards navigation order (the immediate key or index of the item comes last).

The formal model for the fn:pin is that it returns a deep copy of the supplied map or array in which all items in the recursive content have been labeled. This is a useful model because it avoids the need to specify the effect of each individual function and operator on the structure. For example, the rule has the consequence that the result of pin([ 11, 12, 13, 14 ]) => array:remove(3) => array:for-each(fn { label(.)?key }) is [ 1, 2, 4 ]. In a practical implementation, however, it is likely that labels will be attached to items lazily, at the time they are retrieved. Such an implementation will need to recognize pinned maps and arrays and treat them specially when operations such as array:get, array:remove, array:for-each, array:subarray, and their map counterparts, are evaluated.

Because maps and arrays selected from a pinned map or array are themselves pinned, deep lookup operations (whether conducted using the deep lookup operator ??, or the map:find function, or by user-written recursive code) will deliver a labeled value whose parent or ancestor properties can be used to navigate back up through the tree.

For example, given the example map shown in 4.14.1.1 Map Constructors, the expression $map??last[. = "Suciu"] selects the map entry with key "last" and value "Suciu", but by itself gives no information about where this entry was found. By first pinning the map, this extra information can be made available through the label on the result. For example you can select all co-authors of "Suciu" by writing:

pin($map)??last[. = "Suciu"] => label()?ancestors()?author??last

Note:

When an entry in a map, or a member of an array, has the empty sequence as its value, the value contains no items and is therefore unchanged in the pinned version of the containing structure. In addition, the lookup operators ? and ?? flatten their result to a single sequence, so any empty values are effectively discarded from the result. For this reason, pinned arrays and maps work best when all values in arrays and maps are singleton items. An option is therefore provided on the fn:parse-json and fn:json-doc functions to change the representation of JSON null values (whose default is an empty sequence, ()) to a user-supplied value.

Editorial note 
That note is anticipating a proposal in a separate PR.

4.15 Ordered and Unordered Expressions

Changes in 4.0  

  1. The ordered { E } and unordered { E } expressions are retained for backwards compatibility reasons, but in XQuery 4.0 they are deprecated and have no useful effect.   [Issue 1339 ]

OrderedExpr::="ordered" EnclosedExpr
UnorderedExpr::="unordered" EnclosedExpr
EnclosedExpr::="{" Expr? "}"

This syntax is retained from earlier versions of XQuery; in XQuery 4.0 it is deprecated and has no effect.

The constructs ordered { E } and unordered { E } both return the result of evaluating the expression E.

Note:

In addition to ordered and unordered expressions, XQuery provides a function named fn:unordered that operates on any sequence of items and returns the same sequence in an implementation-defined order. A call to the fn:unordered function may be thought of as giving permission for the argument expression to be materialized in whatever order the system finds most efficient. The fn:unordered function relaxes ordering only for the sequence that is its immediate operand, whereas the unordered expression in earlier XQuery versions sets the ordering mode for its operand expression and all nested expressions.

4.16 Conditional Expressions

Changes in 4.0  

  1. Alternative syntax for conditional expressions is available: if (condition) { X } else { Y }, with the else part being optional.   [Issue 234 PR 284 23 January 2023]

XQuery 4.0 allows conditional expressions to be written in several different ways.

IfExpr::="if" "(" Expr ")" (UnbracedActions | BracedActions)
UnbracedActions::="then" ExprSingle "else" ExprSingle
BracedActions::=ThenActionElseIfAction* ElseAction?
ThenAction::=EnclosedExpr
ElseIfAction::="else" "if" "(" Expr ")" EnclosedExpr
ElseAction::="else" EnclosedExpr
EnclosedExpr::="{" Expr? "}"

There are two formats with essentially the same semantics.

Conditional expressions have a special rule for propagating dynamic errors: expressions whose value is not needed for computing the result are guarded, as described in 2.4.5 Guarded Expressions, to prevent spurious dynamic errors.

Here are some examples of conditional expressions:

  • In this example, the test expression is a comparison expression:

    if ($widget1/unit-cost < $widget2/unit-cost)
    then $widget1
    else $widget2
  • In this example, the test expression tests for the existence of an attribute named discounted, independently of its value:

    if ($part/@discounted)
    then $part/wholesale
    else $part/retail
  • The above expression can equivalently be written:

    if ($part/@discounted) {
      $part/wholesale
    } else {
      $part/retail
    }
  • The following example returns the attribute node @discount provided the value of @price is greater than 100; otherwise it returns the empty sequence:

    if (@price gt 100) { @discount }
  • The following example tests a number of conditions:

    if (@code = 1) {
      "food"
    } else if (@code = 2) {
      "fashion"
    } else if (@code = 3) {
      "household"
    } else {
      "general"
    }

Note:

The “dangling else ambiguity” found in many other languages cannot arise:

  • In the unbraced format, both the then and else clauses are mandatory.

  • In the braced format, an else clause is always unambiguously associated with the immediately containing IfExpr.

4.17 Otherwise Expressions

Changes in 4.0  

  1. An otherwise operator is introduced: A otherwise B returns the value of A, unless it is an empty sequence, in which case it returns the value of B.   [Issue 1024 PR 1031 27 February 2024]

OtherwiseExpr::=StringConcatExpr ( "otherwise" StringConcatExpr )*

The otherwise expression returns the value of its first operand, unless this is an empty sequence, in which case it returns the value of its second operand.

For example, @price - (@discount otherwise 0) returns the value of @price - @discount, if the attribute @discount exists, or the value of @price if the @discount attribute is absent.

To prevent spurious errors, the right hand operand is guarded: it cannot throw any dynamic error unless the left-hand operand returns an empty sequence.

Note:

The operator is associative (even under error conditions): A otherwise (B otherwise C) returns the same result as (A otherwise B) otherwise C.

The otherwise operator binds more tightly than comparison operators such as =, but less tightly than string concatenation (||) or arithemetic operators. The expression $a = @x otherwise @y + 1 parses as $a = (@x otherwise (@y + 1)).

4.18 Switch Expressions

Changes in 4.0  

  1. Switch expressions now allow a case clause to match multiple atomic items.   [Issue 328 PR 364 7 March 2023]

  2. Switch and typeswitch expressions can now be written with curly brackets, to improve readability.   [Issue 365 PR 587 7 November 2023]

  3. The comparand expression in a switch expression can be omitted, allowing the switch cases to be provided as arbitrary boolean expressions.   [Issue 671 PR 678 12 September 2023]

SwitchExpr::="switch" SwitchComparand? (SwitchCases | BracedSwitchCases)
SwitchComparand::="(" Expr ")"
SwitchCases::=SwitchCaseClause+ "default" "return" ExprSingle
BracedSwitchCases::="{" SwitchCases "}"
SwitchCaseClause::=("case" SwitchCaseOperand)+ "return" ExprSingle
SwitchCaseOperand::=Expr

The switch expression chooses one of several expressions to evaluate based on the input value.

In a switch expression, the switch keyword is followed by an expression enclosed in parentheses, called the switch comparand. This is the expression whose value is being compared. This expression is optional, and defaults to true(). The remainder of the switch expression consists of one or more case clauses, with one or more case operand expressions each, and a default clause.

The first step in evaluating a switch expression is to apply atomization to the value of the switch comparand. Call the result the switch value. If the switch value is a sequence of length greater than one, a type error is raised [err:XPTY0004]. In the absence of a switch comparand, the switch value is the xs:boolean value true.

The switch value is compared to each SwitchCaseOperand in turn until a match is found or the list is exhausted. The matching is performed as follows:

  1. The SwitchCaseOperand is evaluated.

  2. The resulting value is atomized: call this the case value.

  3. If the case value is an empty sequence, then a match occurs if and only if the switch value is an empty sequence.

  4. Otherwise, the singleton switch value is compared individually with each item in the case value in turn, and a match occurs if and only if these two atomic items compare equal under the rules of the fn:deep-equal function with default options, using the default collation in the static context.

[Definition: The effective case of a switch expression is the first case clause that matches, using the rules given above, or the default clause if no such case clause exists.] The value of the switch expression is the value of the return expression in the effective case.

Switch expressions have rules regarding the propagation of dynamic errors: see 2.4.5 Guarded Expressions. These rules mean that the return clauses of a switch expression must not raise any dynamic errors except in the effective case. Dynamic errors raised in the operand expressions of the switch or the case clauses are propagated; however, an implementation must not raise dynamic errors in the operand expressions of case clauses that occur after the effective case. An implementation is permitted to raise dynamic errors in the operand expressions of case clauses that occur before the effective case, but not required to do so.

The following example shows how a switch expression might be used:

switch ($animal) {
  case "Cow" return "Moo"
  case "Cat" return "Meow"
  case "Duck", "Goose" return "Quack"
  default return "What's that odd noise?"
}

The curly brackets in a switch expression are optional. The above example can equally be written:

switch ($animal) 
  case "Cow" return "Moo"
  case "Cat" return "Meow"
  case "Duck", "Goose" return "Quack"
  default return "What's that odd noise?"

The following example illustrates a switch expression where the comparand is defaulted to true:

switch {
  case ($a le $b) return "lesser"
  case ($a ge $b) return "greater"
  case ($a eq $b) return "equal"
  default return "not comparable"
}

Note:

The comparisons are performed using the fn:deep-equal function, after atomization. This means that a case expression such as @married tests fn:data(@married) rather than fn:boolean(@married). If the effective boolean value of the expression is wanted, this can be achieved with an explicit call of fn:boolean.

4.19 Quantified Expressions

Changes in 4.0  

  1. If a type declaration is present, the supplied values in the input sequence are now coerced to the required type. Type declarations are now permitted in XPath as well as XQuery.   [Issue 1316 PR 1384 13 August 2024]

Quantified expressions support existential and universal quantification. The value of a quantified expression is always true or false.

QuantifiedExpr::=("some" | "every") QuantifierBinding ("," QuantifierBinding)* "satisfies" ExprSingle
QuantifierBinding::=VarNameAndType "in" ExprSingle
TypeDeclaration::="as" SequenceType

A quantified expression begins with a quantifier, which is the keyword some or every, followed by one or more in-clauses that are used to bind variables, followed by the keyword satisfies and a test expression. Each in-clause associates a variable with an expression that returns a sequence of items, called the binding sequence for that variable. The value of the quantified expression is defined by the following rules:

  1. If the QuantifiedExpr contains more than one QuantifierBinding, then it is equivalent to the expression obtained by replacing each comma with satisfies some or satisfies every respectively. For example, the expression some $x in X, $y in Y satisfies $x = $y is equivalent to some $x in X satisfies some $y in Y satisfies $x = $y, while the expression every $x in X, $y in Y satisfies $x lt $y is equivalent to every $x in X satisfies every $y in Y satisfies $x lt $y

  2. If the quantifier is some, the QuantifiedExpr returns true if at least one evaluation of the test expression has the effective boolean valuetrue; otherwise it returns false. In consequence, if the binding sequence is empty, the result of the QuantifiedExpr is false.

  3. If the quantifier is every, the QuantifiedExpr returns true if every evaluation of the test expression has the effective boolean valuetrue; otherwise it returns false. In consequence, if the binding sequence is empty, the result of the QuantifiedExpr is true.

The scope of a variable bound in a quantified expression comprises all subexpressions of the quantified expression that appear after the variable binding. The scope does not include the expression to which the variable is bound.

Each variable binding may be accompanied by a type declaration, which consists of the keyword as followed by the static type of the variable, declared using the syntax in 3.1 Sequence Types. The type declaration defines a required type for the value. At run-time, the supplied value for the variable is converted to the required type by applying the coercion rules. If conversion is not possible, a type error is raised [err:XPTY0004].

The order in which test expressions are evaluated for the various items in the binding sequence is implementation-dependent. If the quantifier is some, an implementation may return true as soon as it finds one item for which the test expression has an effective boolean value of true, and it may raise a dynamic error as soon as it finds one item for which the test expression raises an error. Similarly, if the quantifier is every, an implementation may return false as soon as it finds one item for which the test expression has an effective boolean value of false, and it may raise a dynamic error as soon as it finds one item for which the test expression raises an error. As a result of these rules, the value of a quantified expression is not deterministic in the presence of errors, as illustrated in the examples below.

Here are some examples of quantified expressions:

  • This expression is true if every part element has a discounted attribute (regardless of the values of these attributes):

    every $part in /parts/part satisfies $part/@discounted
  • This expression is true if at least one employee element satisfies the given comparison expression:

    some $emp in /emps/employee satisfies
      $emp/bonus > 0.25 * $emp/salary
  • This expression is true if every employee element has at least one salary child with the attribute current="true":

    every $emp in /emps/employee satisfies
      some $sal in $emp/salary satisfies $sal/@current = 'true'

    Note:

    Like many quantified expressions, this can be simplified. This example can be written every $emp in /emps/employee satisfies $emp/salary[@current = 'true'], or even more concisely as empty(/emps/employee[not(salary/@current = 'true')].

    Another alternative in XQuery 4.0 is to use the higher-order functions fn:some and fn:every. This example can be written fn:every(/emps/employee, fn { salary/@current = 'true' })

  • In the following examples, each quantified expression evaluates its test expression over nine pairs of items, formed from the Cartesian product of the sequences (1, 2, 3) and (2, 3, 4). The expression beginning with some evaluates to true, and the expression beginning with every evaluates to false.

    some $x in (1, 2, 3), $y in (2, 3, 4) satisfies $x + $y = 4
    every $x in (1, 2, 3), $y in (2, 3, 4) satisfies $x + $y = 4
  • This quantified expression may either return true or raise a type error, since its test expression returns true for one item and raises a type error for another:

    some $x in (1, 2, "cat") satisfies $x * 2 = 4
  • This quantified expression may either return false or raise a type error, since its test expression returns false for one item and raises a type error for another:

    every $x in (1, 2, "cat") satisfies $x * 2 = 4
  • This quantified expression returns true, because the binding sequence is empty, despite the fact that the condition can never be satisfied:

    every $x in () satisfies ($x lt 0 and $x gt 0)
  • This quantified expression is implausible because it will always fail with a type error except in the case where $input is an empty sequence. If $input contains one or more xs:date values, a processor must raise a type error on the grounds that an xs:date cannot be compared to an xs:integer. If $input is empty, the processor may (or may not) report this error:

    every $x as xs:date in $input satisfies ($x lt 0)
  • This quantified expression contains a type declaration that is not satisfied by every item in the test expression. The expression may either return true or raise a type error.

    some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4

4.20 Try/Catch Expressions

Changes in 4.0  

  1. $err:map contains entries for all values that are bound to the single variables.   [Issue 32  23 May 2023]

  2. A new variable err:map is available, capturing all error information in one place.   [Issue 32 PR 493 16 May 2023]

  3. $err:stack-trace provides information about the current state of execution.   [Issue 689  1 October 2024]

The try/catch expression provides error handling for dynamic errors and type errors raised during dynamic evaluation, including errors raised by the XQuery implementation and errors explicitly raised in a query using the fn:error() function.

TryCatchExpr::=TryClauseCatchClause+
TryClause::="try" EnclosedExpr
CatchClause::="catch" NameTestUnionEnclosedExpr
NameTestUnion::=(NameTest ++ "|")
NameTest::=EQName | Wildcard
EnclosedExpr::="{" Expr? "}"

A try/catch expression catches dynamic errors and type errors raised by the evaluation of the target expression of the try clause. If the the content expression of the try clause does not raise a dynamic error or a type error, the result of the try/catch expression is the result of the content expression.

If the target expression raises a dynamic error or a type error, the result of the try/catch expression is obtained by evaluating the first catch clause that “matches” the error value, as described below. If no catch clause “matches” the error value, then the try/catch expression raises the error that was raised by the target expression. A catch clause with one or more NameTests matches any error whose error code matches one of these NameTests. For instance, if the error code is err:FOER0000, then it matches a catch clause whose ErrorList is err:FOER0000 | err:FOER0001. Wildcards may be used in NameTests; thus, the error code err:FOER0000 also matches a catch clause whose ErrorList is err:* or *:FOER0000 or *.

Within the scope of the catch clause, a number of variables are implicitly declared, giving information about the error that occurred. These variables are initialized as described in the following table:

VariableTypeValue
$err:codexs:QNameThe error code
$err:descriptionxs:string?A description of the error condition; an empty sequence if no description is available (for example, if the error function was called with one argument).
$err:valueitem()*Value associated with the error. For an error raised by calling the error function, this is the value of the third argument (if supplied).
$err:modulexs:string?The URI (or system ID) of the module containing the expression where the error occurred, or an empty sequence if the information is not available.
$err:line-numberxs:integer?The line number within the module where the error occurred, or an empty sequence if the information is not available. The value may be approximate.
$err:column-numberxs:integer?The column number within the module where the error occurred, or an empty sequence if the information is not available. The value may be approximate.
$err:stack-tracexs:string?Implementation-dependent information about the current state of execution, or an empty sequence if no stack trace is available. The variable must be bound so that a query can reference it without raising an error.
$err:additionalitem()*Implementation-defined. Allows implementations to provide any additional information that might be useful. The variable must be bound so that a query can reference it without raising an error.
$err:mapmap(*)A map with entries for all values that are bound to the variables above. The local names of the variables are assigned as keys. No map entries are created for those values that are empty sequences. The variable can be used to pass on all error information to another function.

Try/catch expressions have a special rule for propagating dynamic errors. The try/catch expression ignores any dynamic errors encountered in catch clauses other than the first catch clause that matches an error raised by the try clause, and these catch clause expressions need not be evaluated.

Static errors are not caught by the try/catch expression.

If a function call occurs within a try clause, errors raised by evaluating the corresponding function are caught by the try/catch expression. If a variable reference is used in a try clause, errors raised by binding a value to the variable are not caught unless the binding expression occurs within the try clause.

Note:

The presence of a try/catch expression does not prevent an implementation from using a lazy evaluation strategy, nor does it prevent an optimizer performing expression rewrites. However, if the evaluation of an expression inside a try/catch is rewritten or deferred in this way, it must take its try/catch context with it. Similarly, expressions that were written outside the try/catch expression may be evaluated inside the try/catch, but only if they retain their original try/catch behavior. The presence of a try/catch does not change the rules that allow the processor to evaluate expressions in such a way that may avoid the detection of some errors.

Here are some examples of try/catch expressions.

  • A try/catch expression without name tests catches any error:

    try {
      $x cast as xs:integer
    } catch * {
      0
    }
  • With the following catch clause, only err:FORG0001 is caught:

    try {
      $x cast as xs:integer
    } catch err:FORG0001 {
      0
    }
  • This try/catch expression specifies that errors err:FORG0001 and err:XPTY0004 are caught:

    try {
      $x cast as xs:integer
    } catch err:FORG0001 | err:XPTY0004 {
      0
    }

    Note:

    In some implementations, err:XPTY0004 is detected during static evaluation; it can only be caught if it is raised during dynamic evaluation.

  • This try/catch expression shows how to return information about the error using implicitly defined error variables:

    try {
      error(QName('http://www.w3.org/2005/xqt-errors', 'err:FOER0000'))
    } catch * {
      $err:code, $err:value, " module: ",
      $err:module, "(", $err:line-number, ",", $err:column-number, ")"
    }
  • Errors raised by using the result of a try/catch expression are not caught, since they are outside the scope of the try expression.

    declare function local:thrice($x as xs:integer) as xs:integer {
      3 * $x
    };
    
    local:thrice(try { "oops" } catch * { 3 } )

    In this example, the try block succeeds, returning the string "oops", which is not a valid argument to the function.

  • All available information about the error is serialized:

    try {
      1 + <empty/>
    } catch * {
      serialize($err:map, {'method':'adaptive'})
    }

4.21 Expressions on SequenceTypes

The instance of, cast, castable, and treat expressions are used to test whether a value conforms to a given type or to convert it to an instance of a given type.

4.21.1 Instance Of

InstanceofExpr::=TreatExpr ( "instance" "of" SequenceType )?

The boolean operator instance of returns true if the value of its first operand matches the SequenceType in its second operand, according to the rules for SequenceType matching; otherwise it returns false. For example:

  • 5 instance of xs:integer

    This example returns true because the given value is an instance of the given type.

  • 5 instance of xs:decimal

    This example returns true because the given value is an integer literal, and xs:integer is derived by restriction from xs:decimal.

  • <a>{ 5 }</a> instance of xs:integer

    This example returns false because the given value is an element rather than an integer.

  • (5, 6) instance of xs:integer+

    This example returns true because the given sequence contains two integers, and is a valid instance of the specified type.

  • . instance of element()

    This example returns true if the context value is a single element node or false if the context value is defined but is not a single element node. If the context value is absentDM, a type error is raised [err:XPDY0002].

Note:

An instance of test does not allow any kind of casting or coercion. The results may therefore be counterintuitive. For example, the expression 3 instance of xs:positiveInteger returns false, because the expression 3 evaluates to an instance of xs:integer, not xs:positiveInteger. For similar reasons, "red" instance of enum("red", "green", "blue") returns false.

On such occasions, a castable as test may be more appropriate: see 4.21.4 Castable

4.21.2 Typeswitch

Changes in 4.0  

  1. Switch and typeswitch expressions can now be written with curly brackets, to improve readability.   [Issue 365 PR 587 7 November 2023]

TypeswitchExpr::="typeswitch" "(" Expr ")" (TypeswitchCases | BracedTypeswitchCases)
TypeswitchCases::=CaseClause+ "default" VarName? "return" ExprSingle
BracedTypeswitchCases::="{" TypeswitchCases "}"
CaseClause::="case" (VarName "as")? SequenceTypeUnion "return" ExprSingle
SequenceTypeUnion::=SequenceType ("|" SequenceType)*

The typeswitch expression chooses one of several expressions to evaluate based on the dynamic type of an input value.

In a typeswitch expression, the typeswitch keyword is followed by an expression enclosed in parentheses, called the operand expression. This is the expression whose type is being tested. The remainder of the typeswitch expression consists of one or more case clauses and a default clause.

Each case clause specifies one or more SequenceTypes followed by a return expression. [Definition: The effective case in a typeswitch expression is the first case clause in which the value of the operand expression matches a SequenceType in the SequenceTypeUnion of the case clause, using the rules of SequenceType matching. ] The value of the typeswitch expression is the value of the return expression in the effective case. If the value of the operand expression does not match any SequenceType named in a case clause, the value of the typeswitch expression is the value of the return expression in the default clause.

In a case or default clause, if the value to be returned depends on the value of the operand expression, the clause must specify a variable name. Within the return expression of the case or default clause, this variable name is bound to the value of the operand expression. Inside a case clause, the static type of the variable is the union of the SequenceTypes named in the SequenceTypeUnion. Inside a default clause, the static type of the variable is the same as the static type of the operand expression. If the value to be returned by a case or default clause does not depend on the value of the operand expression, the clause need not specify a variable.

The scope of a variable binding in a case or default clause comprises that clause. It is not an error for more than one case or default clause in the same typeswitch expression to bind variables with the same name.

Typeswitch expressions have rules regarding the propagation of dynamic errors: see 2.4.5 Guarded Expressions. These rules mean that a typeswitch expression ignores (does not raise) any dynamic errors encountered in case clauses other than the effective case. Dynamic errors encountered in the default clause are raised only if there is no effective case. An implementation is permitted to raise dynamic errors in the operand expressions of case clauses that occur before the effective case, but not required to do so.

The following example shows how a typeswitch expression might be used to process an expression in a way that depends on its dynamic type.

typeswitch($customer/billing-address) {
  case $a as element(*, USAddress)     return $a/state
  case $a as element(*, CanadaAddress) return $a/province
  case $a as element(*, JapanAddress)  return $a/prefecture
  default return "unknown"
}

The curly brackets in a typeswitch expression are optional. The above example can equally be written:

typeswitch($customer/billing-address)
  case $a as element(*, USAddress)     return $a/state
  case $a as element(*, CanadaAddress) return $a/province
  case $a as element(*, JapanAddress)  return $a/prefecture
  default return "unknown"

The following example shows a union of sequence types in a single case:

typeswitch($customer/billing-address) {
  case $a as element(*, USAddress) | element(*, MexicoAddress)
    return $a/state
  case $a as element(*, CanadaAddress)
    return $a/province
  case $a as element(*, JapanAddress)
    return $a/prefecture
  default
    return "unknown"
}

4.21.3 Cast

CastExpr::=ArrowExpr ( "cast" "as" CastTarget "?"? )?
CastTarget::=TypeName | ChoiceItemType | EnumerationType
ChoiceItemType::="(" (ItemType ++ "|") ")"
EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"

Sometimes it is necessary to convert a value to a specific datatype. For this purpose, XQuery 4.0 provides a cast expression that creates a new value of a specific type based on an existing value. A cast expression takes two operands: an input expression and a target type. The type of the atomized value of the input expression is called the input type. The target type must be a generalized atomic type. In practice this means it may be any of:

  • The name of an named item type defined in the static context, which in turn must refer to an item type in one of the following categories.

  • The name of a type defined in the in-scope schema types, which must be a simple type (of variety atomic, list or union) [err:XQST0052] . In addition, the target type cannot be xs:NOTATION, xs:anySimpleType, or xs:anyAtomicType

  • A ChoiceItemType representing a generalized atomic type (such as (xs:date | xs:dateTime)).

  • An EnumerationType such as enum("red", "green", "blue").

Otherwise, a static error is raised [err:XPST0080].

The optional occurrence indicator ? denotes that an empty sequence is permitted.

Casting a node to xs:QName can cause surprises because it uses the static context of the cast expression to provide the namespace bindings for this operation. Instead of casting to xs:QName, it is generally preferable to use the fn:QName function, which allows the namespace context to be taken from the document containing the QName.

The semantics of the cast expression are as follows:

  1. The input expression is evaluated.

  2. The result of the first step is atomized.

  3. If the result of atomization is a sequence of more than one atomic item, a type error is raised [err:XPTY0004].

  4. If the result of atomization is an empty sequence:

    1. If ? is specified after the target type, the result of the cast expression is an empty sequence.

    2. If ? is not specified after the target type, a type error is raised [err:XPTY0004].

  5. If the result of atomization is a single atomic item, the result of the cast expression is determined by casting to the target type as described in Section 21 CastingFO. When casting, an implementation may need to determine whether one type is derived by restriction from another. An implementation can determine this either by examining the in-scope schema definitions or by using an alternative, implementation-dependent mechanism such as a data dictionary. The result of a cast expression is one of the following:

    1. A value of the target type (or, in the case of list types, a sequence of values that are instances of the item type of the list type).

    2. A type error, if casting from the source type to the target type is not supported (for example attempting to convert an integer to a date).

    3. A dynamic error, if the particular input value cannot be converted to the target type (for example, attempting to convert the string "three" to an integer).

    Note:

    Casting to an enumeration type relies on the fact that an enumeration type is a generalized atomic type. So cast $x as enum("red") is equivalent to casting to an anonymous atomic type derived from xs:string whose enumeration facet restricts the value space to the single string "red", while cast $x as enum("red", "green") is equivalent to casting to (enum("red") | enum("green")).

4.21.4 Castable

CastableExpr::=CastExpr ( "castable" "as" CastTarget "?"? )?
CastTarget::=TypeName | ChoiceItemType | EnumerationType
ChoiceItemType::="(" (ItemType ++ "|") ")"
EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"

XQuery 4.0 provides an expression that tests whether a given value is castable into a given target type. The target type is subject to the same rules as the target type of a cast expression.

The expression E castable as T returns true if the result of evaluating E can be successfully cast into the target type T by using a cast expression; otherwise it returns false. If evaluation of E fails with a dynamic error or if the value of E cannot be atomized, the castable expression as a whole fails.

The castable expression can be used as a predicate to avoid errors at evaluation time. It can also be used to select an appropriate type for processing of a given value, as illustrated in the following example:

if ($x castable as hatsize)
then $x cast as hatsize
else if ($x castable as IQ)
then $x cast as IQ
else $x cast as xs:string

Note:

The expression $x castable as enum("red", "green", "blue") is for most practical purposes equivalent to $x = ("red", "green", "blue"); the main difference is that it uses the Unicode codepoint collation for comparing strings, not the default collation from the static context.

4.21.5 Constructor Functions

For every simple type in the in-scope schema types (except xs:NOTATION and xs:anyAtomicType, and xs:anySimpleType, which are not instantiable), a constructor function is implicitly defined. In each case, the name of the constructor function is the same as the name of its target type (including namespace). The signature of the constructor function for a given type depends on the type that is being constructed, and can be found in Section 20 Constructor functionsFO.

There is also a constructor function for every named item type in the static context that expands either to a generalized atomic typeor to a RecordType.

All such constructor functions are classified as system functions.

Note:

The constructor function is present in the static context if and only if the corresponding type is present in the static context.

For XSLT, this means that a constructor function corresponding to an imported schema type is private to the stylesheet package, and a constructor function corresponding to an xsl:item-type declaration has the same visibility as the xsl:item-type declaration.

For XQuery, this means that a constructor function corresponding to an imported schema type is private to the query module, and a constructor function corresponding to a named item type declaration is %public or %private according to the annotations on the item type declaration.

[Definition: The constructor function for a given simple type is used to convert instances of other simple types into the given type. The semantics of the constructor function call T($arg) are defined to be equivalent to the expression $arg cast as T?.]

The following examples illustrate the use of constructor functions:

  • This example is equivalent to "2000-01-01" cast as xs:date?.

    xs:date("2000-01-01")
  • This example is equivalent to ($floatvalue * 0.2E-5) cast as xs:decimal?.

    xs:decimal($floatvalue * 0.2E-5)
  • This example returns an xs:dayTimeDuration value equal to 21 days. It is equivalent to "P21D" cast as xs:dayTimeDuration?.

    xs:dayTimeDuration("P21D")
  • If usa:zipcode is a user-defined atomic type in the in-scope schema types, then the following expression is equivalent to the expression ("12345" cast as usa:zipcode?).

    usa:zipcode("12345")
  • If my:chrono is a named item type that expands to (xs:date | xs:time | xs:dateTime), then the result of my:chrono("12:00:00Z") is the xs:time value 12:00:00Z.

  • If my:location is a named item type that expands to record(latitude as xs:double, longitude as xs:double), then the result of my:location(50.52, -3.02) is the map { 'latitude': 50.52e0, 'longitude': -3.02e0 }.

Note:

An instance of an atomic type whose name is in no namespace can be constructed by using a URIQualifiedName in either a cast expression or a constructor function call. Examples:

17 cast as Q{}apple
Q{}apple(17)

In either context, using an unqualified NCName might not work: in a cast expression, an unqualified name is it is interpreted according to the default namespace for elements and types, while an unqualified name in a constructor function call is resolved using the default function namespace which will often be inappropriate.

4.21.6 Treat

TreatExpr::=CastableExpr ( "treat" "as" SequenceType )?

XQuery 4.0 provides an expression called treat that can be used to modify the static type of its operand.

Like cast, the treat expression takes two operands: an expression and a SequenceType. Unlike cast, however, treat does not change the dynamic type or value of its operand. Instead, the purpose of treat is to ensure that an expression has an expected dynamic type at evaluation time.

The semantics of expr1 treat as type1 are as follows:

  • During static analysis:

    The static type of the treat expression is type1. This enables the expression to be used as an argument of a function that requires a parameter of type1.

  • During expression evaluation:

    If expr1 matches type1, using the rules for SequenceType matching, the treat expression returns the value of expr1; otherwise, it raises a dynamic error [err:XPDY0050]. If the value of expr1 is returned, the identity of any nodes in the value is preserved. The treat expression ensures that the value of its expression operand conforms to the expected type at run-time.

  • Example:

    $myaddress treat as element(*, USAddress)

    The static type of $myaddress may be element(*, Address), a less specific type than element(*, USAddress). However, at run-time, the value of $myaddress must match the type element(*, USAddress) using rules for SequenceType matching; otherwise a dynamic error is raised [err:XPDY0050].

Note:

Earlier releases of XPath and XQuery defined a mode of operation, sometimes called strict static typing, in which it was required that the static type of every expression should conform to the required type of the context in which it appeared. In this situation it was often necessary to define a more precise static type for an expression by the use of treat as. In the absence of this feature, the treat as expression is rarely necessary, though it can be useful for documentation, and might in some cases (depending on the processor) have performance benefits.

4.22 Simple map operator (!)

SimpleMapExpr::=PathExpr ("!" PathExpr)*

A mapping expression S!E evaluates the expression E once for every item in the sequence obtained by evaluating S. The simple mapping operator ! can be applied to any sequence, regardless of the types of its items, and it can deliver a mixed sequence of nodes, atomic items, and functions. Unlike the similar / operator, it does not sort nodes into document order or eliminate duplicates.

Each operation E1!E2 is evaluated as follows: Expression E1 is evaluated to a sequence S. Each item in S then serves in turn to provide an inner focus (the item as the context value, its position in S as the context position, the length of S as the context size) for an evaluation of E2 in the dynamic context. The sequences resulting from all the evaluations of E2 are combined as follows: Every evaluation of E2 returns a (possibly empty) sequence of items. The final result is the sequence concatenation of these sequences. The returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2.

Simple map operators have functionality similar to 4.6.3 Path operator (/). The following table summarizes the differences between these two operators

OperatorPath operator (E1 / E2)Simple map operator (E1 ! E2)
E1Any sequence of nodesAny sequence of items
E2Either a sequence of nodes or a sequence of non-node itemsA sequence of items
Additional processingDuplicate elimination and document orderingSimple sequence concatenation

The following examples illustrate the use of simple map operators combined with path expressions.

  • child::div1 / child::para / string() ! concat("id-", .)

    Selects the para element children of the div1 element children of the context node; that is, the para element grandchildren of the context node that have div1 parents. It then outputs the strings obtained by prepending "id-" to each of the string values of these grandchildren.

  • $emp ! (@first, @middle, @last)

    Returns the values of the attributes first, middle, and last for each element in $emp, in the order given. (The / operator, if used here, would return the attributes in an unpredictable order.)

  • $docs ! ( //employee)

    Returns all the employee elements within all the documents identified by the variable $docs, in document order within each document, but retaining the order of documents.

  • avg( //employee / salary ! translate(., '$', '') ! number(.))

    Returns the average salary of the employees, having converted the salary to a number by removing any $ sign and then converting to a number. (The second occurrence of ! could not be written as / because the left-hand operand of / cannot be an atomic item.)

  • string-join((1 to $n) ! "*")

    Returns a string containing $n asterisks.

  • $values ! (.*.) => sum()

    Returns the sum of the squares of a sequence of numbers.

  • string-join(ancestor::* ! name(), '/')

    Returns the names of ancestor elements, joined by / characters, i.e., the path to the parent of the context.

4.23 Arrow Expressions

Arrow expressions apply a function to a value, using the value of the left-hand expression as the first argument to the function.

ArrowExpr::=UnaryExpr ( (SequenceArrowTarget | MappingArrowTarget | LookupArrowTarget) )*
SequenceArrowTarget::="=>" ArrowTarget
MappingArrowTarget::="=!>" ArrowTarget
LookupArrowTarget::="=?>" NCNamePositionalArgumentList
ArrowTarget::=(ArrowStaticFunctionArgumentList) | (ArrowDynamicFunctionPositionalArgumentList)
ArrowStaticFunction::=EQName
ArrowDynamicFunction::=VarRef | InlineFunctionExpr | ParenthesizedExpr
InlineFunctionExpr::=Annotation* ("function" | "fn") FunctionSignature? FunctionBody
ArgumentList::="(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
PositionalArgumentList::="(" PositionalArguments? ")"

The arrow syntax is particularly helpful when applying multiple functions to a value in turn. For example, the following expression invites syntax errors due to misplaced parentheses:

tokenize((normalize-unicode(upper-case($string))),"\s+")

In the following reformulation, it is easier to see that the parentheses are balanced:

$string => upper-case() => normalize-unicode() => tokenize("\s+")

When the operator is written as =!>, the function is applied to each item in the sequence in turn. Assuming that $string is a single string, the above example could equally be written:

$string =!> upper-case() =!> normalize-unicode() =!> tokenize("\s+")

The difference between the two operators is seen when the left-hand operand evaluates to a sequence:

(1, 2, 3) => avg()

returns a value of only one item, 2, the average of all three items, whereas

(1, 2, 3) =!> avg()

returns the original sequence of three items, (1, 2, 3), each item being the average of itself. The following example:

"The cat sat on the mat"
=> tokenize()
=!> concat(".")
=!> upper-case()
=> string-join(" ")

returns "THE. CAT. SAT. ON. THE. MAT.". The first arrow could be written either as => or =!> because the operand is a singleton; the next two arrows have to be =!> because the function is applied to each item in the tokenized sequence individually; the final arrow must be => because the string-join function applies to the sequence as a whole.

Note:

It may be useful to think of this as a map/reduce pipeline. The functions introduced by =!> are mapping operations; the function introduced by => is a reduce operation.

The following example introduces an inline function to the pipeline:

(1 to 5) =!> xs:double() =!> math:sqrt() =!> fn($a) { $a + 1 }() => sum()

This is equivalent to sum((1 to 5) ! (math:sqrt(xs:double(.)) + 1)).

The same effect can be achieved using a focus function:

(1 to 5) =!> xs:double() =!> math:sqrt() =!> fn { . + 1 }() => sum()

Where the value of an expression is a map containing functions, simulating the behavior of objects in object-oriented languages, then the lookup arrow operator=?> can be used to retrive a function from the map and to invoke the function with the map as its first argument. For example, if my:rectangle returns a map with entries width, height, expand, and area, then it becomes possible to write:

my:rectangle(3, 5) =?> expand(2) =?> area()

Note:

The ArgumentList may include PlaceHolders, though this is not especially useful. For example, the expression "$" => concat(?) is equivalent to concat("$", ?): its value is a function that prepends a supplied string with a $ symbol.

Note:

The ArgumentList may include keyword arguments if the function is identified statically (that is, by name). For example, the following is valid: $xml => xml-to-json(indent := true()) => parse-json(escape := false()).

The sequence arrow operator thus applies the supplied function to the left-hand operand as a whole, while the mapping arrow operator applies the function to each item in the value of the left-hand operand individually. In the case where the result of the left-hand operand is a single item, the two operators have the same effect.

Note:

The mapping arrow symbol =!> is intended to suggest a combination of function application (=>) and sequence mapping (!) combined in a single operation.

Similarly, the lookup arrow symbol =?> is intended to suggest a combination of function application (=>) and map lookup (?) in a single operation.

4.23.1 Sequence Arrow Expressions

[Definition: The sequence arrow operator=> applies a function to a supplied sequence.] It is defined as follows:

4.23.2 Mapping Arrow Expressions

Changes in 4.0  

  1. The arrow operator => is now complemented by a “mapping arrow” operator =!> which applies the supplied function to each item in the input sequence independently.

[Definition: The mapping arrow operator=!> applies a function to each item in a sequence.] It is defined as follows:

4.23.3 Lookup Arrow Expressions

Changes in 4.0  

  1. With the lookup arrow expression and the =?> operator, a function in a map can be looked up and called with the map as first argument.   [ PR 985 13 February 2024]

The lookup arrow expression simulates the behavior of method invocations in object-oriented languages. It is useful for invoking functions that are contained as entries in maps.

For example, the expression

let $rectangle := {
  "width": 20,
  "height": 12,
  "area": fn($this) { $this?width * $this?height }
} 
return $rectangle =?> area()

returns the value 240.

An expression such as M =?> N(A, B, C) is evaluated as follows:

  1. The left-hand expression M is evaluated. If the value is an empty sequence, then the result of the expression is an empty sequence. If it is non-empty then it must be a single map: call it $m.

  2. The lookup expression $m?N is evaluated. The result must be a single function item: call it $f.

  3. The dynamic function call $f($m, A, B, C) is evaluated, and the result is returned.

Any of the above steps can lead to errors:

  1. A type error [err:XPTY0004] is raised if the value of the left hand expression does not match the type map(*)?.

  2. A type error [err:XPTY0004] is raised if the value of the lookup expression $m?N does not match the type function(*), or if the arity of the function is not equal to the number of arguments in the argument list plus one.

  3. An error may occur in evaluating the dynamic function call, for example if the function does not expect a map to be supplied as the first argument.

4.24 Validate Expressions

Changes in 4.0  

  1. The rules concerning the interpretation of xsi:schemaLocation and xsi:noNamespaceSchemaLocation attributes have been tightened up.   [Issue 729 PR 1254 8 June 2024]

ValidateExpr::="validate" (ValidationMode | ("type" TypeName))? "{" Expr "}"
ValidationMode::="lax" | "strict"
EnclosedExpr::="{" Expr? "}"

A validate expression can be used to validate a document node or an element node with respect to the in-scope schema definitions, using the schema validation process defined in [XML Schema 1.0] or [XML Schema 1.1]. If the operand of a validate expression does not evaluate to exactly one document or element node, a type error is raised [err:XQTY0030]. In this specification, the node that is the operand of a validate expression is called the operand node.

A validate expression returns a new node with its own identity and with no parent. The new node and its descendants are given type annotation that are generated by applying a validation process to the operand node. In some cases, default values may also be generated by the validation process.

A validate expression may optionally specify a validation mode. The default validation mode (applicable when no type name is provided) is strict.

A validate expression may optionally specify a TypeName. This type name must be found in the in-scope schema definitions; if it is not, a static error is raised [err:XQST0104]. If the type name is unprefixed, it is interpreted according to the default namespace for elements and types.

The result of a validate expression is defined by the following rules.

  1. If the operand node is a document node, its children must consist of exactly one element node and zero or more comment and processing instruction nodes, in any order; otherwise, a dynamic error [err:XQDY0061] is raised.

  2. The operand node is converted to an XML Information Set ([XML Infoset]) according to the “Infoset Mapping” rules defined in [XQuery and XPath Data Model (XDM) 4.0]. Note that this process discards any existing type annotations. Validity assessment is carried out on the root element information item of the resulting Infoset, using the in-scope schema definitions as the effective schema. The process of validation applies recursively to contained elements and attributes to the extent required by the effective schema.

  3. If a type name is provided, and the type name is xs:untyped, all elements receive the type annotation xs:untyped, and all attributes receive the type annotation xs:untypedAtomic. If the type name is xs:untypedAtomic, the node receives the type annotation xs:untypedAtomic; a type error [err:XPTY0004] is raised if the node has element children. Otherwise, schema-validity assessment is carried out according to the rules defined in [XML Schema 1.0] or [XML Schema 1.1] Part 1, section 3.3.4 "Element Declaration Validation Rules", “Validation Rule: Schema-Validity Assessment (Element)”, clauses 1.2 and 2, using this type definition as the “processor-stipulated type definition” for validation.

    If the instance being validated contains an xml:id attribute, both lax and strict validation cause this attribute to be subjected to [xml:id] processing: that is, the attribute is checked for uniqueness, and is typed as xs:ID, and the containing element is therefore eligible as a target for the id() function.

  4. It is implementation defined whether the validity assessment process takes account of any xsi:schemaLocation or xsi:noNamespaceSchemaLocation attributes in the tree being validated. If it does so, then it should adhere to the following rules:

    1. Any schema loaded using these attributes must be compatibleDM with the schema in the static context from which validation is invoked.

    2. Any schema loaded using these attributes must not override or redefine any schema components in the static context.

    3. Any schema components loaded using this mechanism must be used for this validity assessment only, and must not affect the outcome of any subsequent validity assessments of other documents.

      Note:

      A processor may choose to cache such schema components but the existence of such a cache should only affect performance, not the validation outcome.

    A consequence of validating a document using schema components that are not in the static context is that nodes may be annotated with types that are not in the static context. But the rules for schema compatibilityDM mean that this is not a problem.

  5. When no type name is provided:

    1. If validation mode is strict, then there must be a top-level element declaration in the in-scope element declarations that matches the root element information item in the Infoset, and schema-validity assessment is carried out using that declaration in accordance with [XML Schema 1.0] Part 1, section 5.2, “Assessing Schema-Validity”, item 2, or [XML Schema 1.1] Part 1, section 5.2, “Assessing Schema-Validity”, “element-driven validation”. If there is no such element declaration, a dynamic error is raised [err:XQDY0084].

    2. If validation mode is lax, then schema-validity assessment is carried out in accordance with [XML Schema 1.0] Part 1, section 5.2, “Assessing Schema-Validity”, item 3, or [XML Schema 1.1] Part 1, section 5.2, “Assessing Schema-Validity”, “lax wildcard validation”.

      If validation mode is lax and the root element information item has neither a top-level element declaration nor an xsi:type attribute, [XML Schema 1.0] defines the recursive checking of children and attributes as optional. During processing of an XQuery validate expression, this recursive checking is required.

    3. If the operand node is an element node, the validation rules named “Validation Root Valid (ID/IDREF)” are not applied. This means that document-level constraints relating to uniqueness and referential integrity are not enforced.

    4. There is no check that the document contains unparsed entities whose names match the values of nodes of type xs:ENTITY or xs:ENTITIES.

    Note:

    Validity assessment is affected by the presence or absence of xsi:type attributes on the elements being validated, and may generate new information items such as default attributes.

  6. The outcome of the validation expression depends on the validity property of the root element information item in the PSVI that results from the validation process.

    1. If the validity property of the root element information item is valid, or if validation mode is lax and the validity property of the root element information item is notKnown, the PSVI is converted back into an XDM instance as described in [XQuery and XPath Data Model (XDM) 4.0] Section 3.3, “Construction from a PSVI”. The resulting node (a new node of the same kind as the operand node) is returned as the result of the validate expression.

    2. Otherwise, a dynamic error is raised [err:XQDY0027].

Note:

The effect of these rules is as follows, where the validated element means either the operand node or (if the operand node is a document node) its element child.:

  • If validation mode is strict, the validated element must have a top-level element declaration in the effective schema, and must conform to this declaration.

  • If validation mode is lax, the validated element must conform to its top-level element declaration if such a declaration exists in the effective schema. If validation mode is lax and there is no top-level element declaration for the element, and the element has an xsi:type attribute, then the xsi:type attribute must name a top-level type definition in the effective schema, and the element must conform to that type.

  • If a type name is specified in the validate expression, no attempt is made to locate an element declaration matching the name of the validated element; the element can have any name, and its content is validated against the named type.

Note:

During conversion of the PSVI into an XDM instance after validation, any element information items whose validity property is notKnown are converted into element nodes with type annotationxs:anyType, and any attribute information items whose validity property is notKnown are converted into attribute nodes with type annotationxs:untypedAtomic, as described in Section 3.3.1.1 Element and Attribute Node TypesDM.

Note:

A query might take as its primary input a document conforming to schema X, and produce as its primary output a document conforming to schema Y. To be sure that the output is indeed valid against schema Y, the safest course of action is to evaluate a validate expression within a query module that imports schema Y and nothing else. Otherwise, if the validation occurs within a module that imports both X and Y, the outcome of validation might differ because of the differences between the two schemas.

4.25 Extension Expressions

[Definition: An extension expression is an expression whose semantics are implementation-defined.] Typically a particular extension will be recognized by some implementations and not by others. The syntax is designed so that extension expressions can be successfully parsed by all implementations, and so that fallback behavior can be defined for implementations that do not recognize a particular extension.

ExtensionExpr::=Pragma+ "{" Expr? "}"
Pragma::="(#" S? EQName (SPragmaContents)? "#)"
/* ws: explicit */
PragmaContents::=(Char* - (Char* '#)' Char*))

An extension expression consists of one or more pragmas, followed by an optional expression (the associated expression). [Definition: A pragma is denoted by the delimiters (# and #), and consists of an identifying EQName followed by implementation-defined content.] The content of a pragma may consist of any string of characters that does not contain the ending delimiter #). If the EQName of a pragma is a lexical QName, it must resolve to a namespace URI and local name, using the statically known namespaces [err:XPST0081]. If the EQName is an unprefixed NCName, it is interpreted as a name in no namespace (and the pragma is therefore ignored).

Each implementation recognizes an implementation-defined set of namespace URIs used to denote pragmas.

If the namespace URI of a pragma’s expanded QName is not recognized by the implementation as a pragma namespace, or if the name is in no namespace, then the pragma is ignored. If all the pragmas in an ExtensionExpr are ignored, then the value of the ExtensionExpr is the value of the associated expression; if no associated expression is provided, a static error is raised [err:XQST0079].

If an implementation recognizes the namespace of one or more pragmas in an ExtensionExpr, then the value of the ExtensionExpr, including its error behavior, is implementation-defined. For example, an implementation that recognizes the namespace of a pragma’s expanded QName, but does not recognize the local part of the name, might choose either to raise an error or to ignore the pragma.

It is a static error [err:XQST0013] if an implementation recognizes a pragma but determines that its content is invalid.

If an implementation recognizes a pragma, it must report any static errors in the following expression even if it will not evaluate that expression.

Note:

The following examples illustrate three ways in which extension expressions might be used.

  • A pragma can be used to furnish a hint for how to evaluate the following expression, without actually changing the result. For example:

    declare namespace exq = "http://example.org/XQueryImplementation";
    (# exq:use-index #) {
      $bib/book/author[name = 'Berners-Lee']
    }

    An implementation that recognizes the exq:use-index pragma might use an index to evaluate the expression that follows. An implementation that does not recognize this pragma would evaluate the expression in its normal way.

  • A pragma might be used to modify the semantics of the following expression in ways that would not (in the absence of the pragma) be conformant with this specification. For example, a pragma might be used to permit comparison of xs:duration values using implementation-defined semantics (this would normally be an error). Such changes to the language semantics must be scoped to the enclosed expression following the pragma.

  • A pragma might contain syntactic constructs that are evaluated in place of the following expression. In this case, the following expression itself (if it is present) provides a fallback for use by implementations that do not recognize the pragma. For example:

    declare namespace exq = "http://example.org/XQueryImplementation";
    
    for $x in (# exq:distinct //city by @country #) {
      //city[not(@country = preceding::city/@country)]
    }
    return f:show-city($x)

    Here an implementation that recognizes the pragma will return the result of evaluating the proprietary syntax exq:distinct //city by @country, while an implementation that does not recognize the pragma will instead return the result of the expression //city[not(@country = preceding::city/@country)]. If no fallback expression is required, or if none is feasible, then the expression between the curly brackets may be omitted, in which case implementations that do not recognize the pragma will raise a static error.

5 Modules and Prologs

Module::=VersionDecl? (LibraryModule | MainModule)
MainModule::=PrologQueryBody
LibraryModule::=ModuleDeclProlog
Prolog::=((DefaultNamespaceDecl | Setter | NamespaceDecl | Import) Separator)* ((ContextValueDecl | AnnotatedDecl | OptionDecl) Separator)*
Setter::=BoundarySpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl | DecimalFormatDecl
Import::=SchemaImport | ModuleImport
Separator::=";"
QueryBody::=Expr

A query can be assembled from one or more fragments called modules. [Definition: A module is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.3.3 Expression Processing. Each module is either a main module or a library module.]

[Definition: A main module consists of a Prolog followed by a Query Body.] A query has exactly one main module. In a main module, the Query Body is evaluated with respect to the static and dynamic contexts of the main module in which it is found, and its value is the result of the query.

[Definition: A module that does not contain a Query Body is called a library module. A library module consists of a module declaration followed by a Prolog.] A library module cannot be evaluated directly; instead, it provides function and variable declarations that can be imported into other modules.

The XQuery syntax does not allow a module to contain both a module declaration and a Query Body.

[Definition: A Prolog is a series of declarations and imports that define the processing environment for the module that contains the Prolog.] Each declaration or import is followed by a semicolon. A Prolog is organized into two parts.

The first part of the Prolog consists of setters, imports, namespace declarations, and default namespace declarations. [Definition: Setters are declarations that set the value of some property that affects query processing, such as construction mode or default collation.] Namespace declarations and default namespace declarations affect the interpretation of lexical QNames within the query. Imports are used to import definitions from schemas and modules. [Definition: The target namespace of a module is the namespace of the objects (such as elements or functions) that it defines. ]

The second part of the Prolog consists of declarations of variables, functions, and options. These declarations appear at the end of the Prolog because they may be affected by declarations and imports in the first part of the Prolog.

[Definition: The Query Body, if present, consists of an expression that defines the result of the query.] Evaluation of expressions is described in 4 Expressions. A module can be evaluated only if it has a Query Body.

5.1 Version Declaration

VersionDecl::="xquery" (("encoding" StringLiteral) | ("version" StringLiteral ("encoding" StringLiteral)?)) Separator

[Definition: A version declaration can identify the applicable XQuery syntax and semantics for a module, as well as its encoding.]

[Definition: An XQuery version number consists of two integers, referred to as the major version number and the minor version number.]

The version number is written as a StringLiteral following the version keyword, and in a conformant XQuery 4.0 query it must match the regular expression [1-9][0-9]*\.[0-9]: for example "4.0". The major version is the integer preceding the dot (which must be written without any leading zero); the minor version is the integer after the dot (which must be a single digit).

Note:

XQuery 1.0 and 3.0 allowed the version number to be any string; XQuery 3.1 constrained it to consist of two integers separated by a dot. This left it unclear, for example, whether "3.01" was the same version number as "3.1", or whether "3.10" represented a higher version than "3.2". In 4.0 the rules have therefore been made stricter, to avoid any ambiguity.

If the version declaration is not present or the version is not included in the declaration, an XQuery 4.0 processor assumes a version of "4.0", unless configured otherwise using some external mechanism.

The version number "4.0" indicates the intent that the module be processed by an XQuery 4.0 processor.

An XQuery 4.0 processor must accept a module in which the version number is given as "1.0", "3.0", or "3.1". It is then implementation defined whether the module is processed using the syntax and semantics of the XQuery 4.0 specification, or the rules of the relevant earlier version. For example, if a query module specifies version "3.0" but contains a call to the parse-html function, the processor at its option can either raise an error, or process the function call according to the XQuery 4.0 specification.

The XQuery 4.0 specification does not attempt to define the semantics of a query in which different modules use different version numbers. One approach is to process all modules as if they specified version "4.0". Another approach (which may be appropriate if modules are separately compiled) is to process each module using its own version number; but it is then implementation defined what happens if (say) a 3.1 module imports a 4.0 library module that declares a function with a signature that 3.1 does not recognize.

A conformant XQuery 4.0 processor may raise an error if the version number is anything other than "1.0", "3.0", "3.1", or "4.0". If the processor does not raise an error, the effect of such a query is implementation defined.

Note:

The effect of this rule is to permit the use of non-standard version numbers to label non-standard extensions of the XQuery language. It also leaves flexibility as to how an XQuery 4.0 processor should handle future version numbers such as "4.1", or version numbers such as "1" or "3.00" that were permitted by earlier XQuery specifications.

If a query is rejected because of a version mismatch with the processor, a static error [err:XQST0031] must be raised.

[Definition: If present, a version declaration may optionally include an encoding declaration. The value of the string literal following the keyword encoding is an encoding name, and must conform to the definition of EncName specified in [XML 1.0] [err:XQST0087]. The purpose of an encoding declaration is to allow the writer of a query to provide a string that indicates how the query is encoded, such as "UTF-8", "UTF-16", or "US-ASCII".] Since the encoding of a query may change as the query moves from one environment to another, there can be no guarantee that the encoding declaration is correct.

The handling of an encoding declaration is implementation-dependent. If an implementation has a priori knowledge of the encoding of a query, it may use this knowledge and disregard the encoding declaration. The semantics of a query are not affected by the presence or absence of an encoding declaration.

If a version declaration is present, no Comment may occur before the end of the version declaration. If such a Comment is present, the result is implementation-dependent; an implementation may raise an implementation-dependent static error, or ignore the comment.

Note:

The effect of a Comment before the end of a version declaration is implementation-dependent because it may suppress query processing by interfering with detection of the encoding declaration.

The following examples illustrate version declarations:

xquery version "3.1";
xquery version "4.0" encoding "utf-8";

5.2 Module Declaration

ModuleDecl::="module" "namespace" NCName "=" URILiteralSeparator

[Definition: A module declaration serves to identify a module as a library module. A module declaration begins with the keyword module and contains a namespace prefix and a URILiteral.] The URILiteral must be of nonzero length [err:XQST0088]. The URILiteral identifies the target namespace of the library module, which is the namespace for all variables and functions exported by the library module. The name of every variable and function declared in a library module must have a namespace URI that is the same as the target namespace of the module; otherwise a static error is raised [err:XQST0048]. The (prefix,URI) pair is added to the set of statically known namespaces.

The namespace prefix specified in a module declaration must not be xml or xmlns [err:XQST0070], and must not be the same as any namespace prefix bound in the same module by a schema import, by a namespace declaration, or by a module import with a different target namespace [err:XQST0033].

Any module may import one or more library modules by means of a module import that specifies the target namespace of the library modules to be imported. When a module imports one or more library modules, the variables and functions declared in the imported modules are added to the static context and (where applicable) to the dynamic context of the importing module.

The following is an example of a module declaration:

module namespace gis = "http://example.org/gis-functions";

5.3 Boundary-space Declaration

BoundarySpaceDecl::="declare" "boundary-space" ("preserve" | "strip")

[Definition: A boundary-space declaration sets the boundary-space policy in the static context, overriding any implementation-defined default. Boundary-space policy controls whether boundary whitespace is preserved by element constructors during processing of the query.] If boundary-space policy is preserve, boundary whitespace is preserved. If boundary-space policy is strip, boundary whitespace is stripped (deleted). A further discussion of whitespace in constructed elements can be found in 4.12.1.4 Boundary Whitespace.

The following example illustrates a boundary-space declaration:

declare boundary-space preserve;

If a Prolog contains more than one boundary-space declaration, a static error is raised [err:XQST0068].

5.4 Default Collation Declaration

DefaultCollationDecl::="declare" "default" "collation" URILiteral

[Definition: A default collation declaration sets the value of the default collation in the static context, overriding any implementation-defined default.] The default collation is the collation that is used by functions and operators that require a collation if no other collation is specified. For example, the gt operator on strings is defined by a call to the fn:compare function, which takes an optional collation parameter. Since the gt operator does not specify a collation, the fn:compare function implements gt by using the default collation.

If neither the implementation nor the Prolog specifies a default collation, the Unicode codepoint collation (http://www.w3.org/2005/xpath-functions/collation/codepoint) is used.

The following example illustrates a default collation declaration:

declare default collation "http://example.org/languages/Icelandic";

If a default collation declaration specifies a collation by a relative URI, that relative URI is resolved to an absolute URI using the Static Base URI. If a Prolog contains more than one default collation declaration, or the value specified by a default collation declaration (after resolution of a relative URI, if necessary) is not present in statically known collations, a static error is raised [err:XQST0038].

5.5 Base URI Declaration

BaseURIDecl::="declare" "base-uri" URILiteral

[Definition: A base URI declaration specifies the Static Base URI property. The Static Base URI property is used when resolving relative URI references.] For example, the Static Base URI property is used when resolving relative references for module import and for the fn:doc function.

Note:

As discussed in the definition of Static Base URI, if there is no base URI declaration, or if the value of the declaration is a relative URI reference, then the value of the Static Base URI may depend on the location of the query, and it is permissible for this to vary between the static analysis phase and the dynamic evaluation phase.

The following is an example of a base URI declaration:

declare base-uri "http://example.org";

If a Prolog contains more than one base URI declaration, a static error is raised [err:XQST0032].

In the terminology of [RFC3986] Section 5.1, the URILiteral of the base URI declaration is considered to be a “base URI embedded in content”. If no base URI declaration is present, Static Base URI property is established according to the principles outlined in [RFC3986] Section 5.1—that is, it defaults first to the base URI of the encapsulating entity, then to the URI used to retrieve the entity, and finally to an implementation-defined default. If the URILiteral in the base URI declaration is a relative URI, then it is made absolute by resolving it with respect to this same hierarchy. For example, if the URILiteral in the base URI declaration is ../data/, and the query is contained in a file whose URI is file:///C:/temp/queries/query.xq, then the Static Base URI property is file:///C:/temp/data/.

It is not intrinsically an error if this process fails to establish an absolute base URI; however, the Static Base URI property is then absentDM [err:XPST0001]. When the Static Base URI property is absentDM, any attempt to use its value to resolve a relative URI reference will result in an error [err:XPST0001].

5.6 Construction Declaration

ConstructionDecl::="declare" "construction" ("strip" | "preserve")

[Definition: A construction declaration sets the construction mode in the static context, overriding any implementation-defined default.] The construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xs:untyped; all element nodes copied during node construction receive the type xs:untyped, and all attribute nodes copied during node construction receive the type xs:untypedAtomic.

The following example illustrates a construction declaration:

declare construction strip;

If a Prolog specifies more than one construction declaration, a static error is raised [err:XQST0067].

5.7 Ordering Mode Declaration

Changes in 4.0  

  1. The ordering mode declaration is retained for backwards compatibility reasons, but in XQuery 4.0 it is deprecated and has no useful effect.   [Issue 1339 ]

OrderingModeDecl::="declare" "ordering" ("ordered" | "unordered")

The ordering mode declaration is retained from earlier XQuery versions, but in XQuery 4.0 it is deprecated and has no effect.

Note:

That is to say, XQuery 4.0 always operates as if ordering mode were set to ordered in earlier versions.

If a Prolog contains more than one ordering mode declaration, a static error is raised [err:XQST0065].

5.8 Empty Order Declaration

EmptyOrderDecl::="declare" "default" "order" "empty" ("greatest" | "least")

[Definition: An empty order declaration sets the default order for empty sequences in the static context, overriding any implementation-defined default. This declaration controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression.] An individual order by clause may override the default order for empty sequences by specifying empty greatest or empty least.

The following example illustrates an empty order declaration:

declare default order empty least;

If a Prolog contains more than one empty order declaration, a static error is raised [err:XQST0069].

5.9 Copy-Namespaces Declaration

CopyNamespacesDecl::="declare" "copy-namespaces" PreserveMode "," InheritMode
PreserveMode::="preserve" | "no-preserve"
InheritMode::="inherit" | "no-inherit"

[Definition: A copy-namespaces declaration sets the value of copy-namespaces mode in the static context, overriding any implementation-defined default. Copy-namespaces mode controls the namespace bindings that are assigned when an existing element node is copied by an element constructor or document constructor.] Handling of namespace bindings by element constructors is described in 4.12.1 Direct Element Constructors.

The following example illustrates a copy-namespaces declaration:

declare copy-namespaces preserve, no-inherit;

If a Prolog contains more than one copy-namespaces declaration, a static error is raised [err:XQST0055].

5.10 Decimal Format Declaration

Changes in 4.0  

  1. Several decimal format properties, including minus sign, exponent separator, percent, and per-mille, can now be rendered as arbitrary strings rather than being confined to a single character.   [Issue 1048 PR 1250 3 June 2024]

DecimalFormatDecl::="declare" (("decimal-format" EQName) | ("default" "decimal-format")) (DFPropertyName "=" StringLiteral)*
DFPropertyName::="decimal-separator" | "grouping-separator" | "infinity" | "minus-sign" | "NaN" | "percent" | "per-mille" | "zero-digit" | "digit" | "pattern-separator" | "exponent-separator"

[Definition: A decimal format declaration adds a decimal format to the statically known decimal formats, which define the properties used to format numbers using the fn:format-number() function], as described in [XQuery and XPath Functions and Operators 4.0]. If the form decimal-format EQName is used, then the declaration defines the properties of the decimal format whose name is EQName, while the form default decimal-format defines the properties of the unnamed decimal format. The declaration contains a set of (DFPropertyName, StringLiteral) pairs, where the DFPropertyName is the name of the property and the StringLiteral is its value. The valid values and default values for each property are defined in statically known decimal formats.

If a format declares no properties, default values are used for all properties.

Error conditions are defined as follows:

The following query formats numbers using two different decimal format declarations:

declare decimal-format local:de decimal-separator = "," grouping-separator = "."; 
declare decimal-format local:en decimal-separator = "." grouping-separator = ","; 
       
let $numbers := (1234.567, 789, 1234567.765) 
for $i in $numbers
return ( 
  format-number($i, "#.###,##", "local:de"), 
  format-number($i, "#,###.##", "local:en") 
)

The output of this query is:

1.234,57 1,234.57 789 789 1.234.567,76 1,234,567.76

5.11 Schema Import

Changes in 4.0  

  1. In previous versions the interpretation of location hints in import schema declarations was entirely at the discretion of the processor. To improve interoperability, XQuery 4.0 recommends (but does not mandate) a specific strategy for interpreting these hints.  [Issue 647 PR 659 24 October 2023]

  2. The rules for the consistency of schemas imported by different query modules, and for consistency between imported schemas and those used for validating input documents, have been defined with greater precision. It is now recognized that these schemas will not always be identical, and that validation with respect to different schemas may produce different outcomes, even if the components of one are a subset of the components of the other.  [Issue 451 PR 635]

SchemaImport::="import" "schema" SchemaPrefix? URILiteral ("at" (URILiteral ++ ","))?
SchemaPrefix::=("namespace" NCName "=") | ("fixed"? "default" "element" "namespace")

[Definition: A schema import imports the element declarations, attribute declarations, and type definitions from a schema into the in-scope schema definitions. For each named user-defined simple type in the schema, schema import also adds a corresponding constructor function. ] The schema to be imported is identified by its target namespace. The schema import may bind a namespace prefix to the target namespace of the imported schema, adding the (prefix, URI) pair to the statically known namespaces, or it may declare that target namespace to be the default namespace for elements and types. The schema import may also provide optional hints for locating the schema.

The namespace prefix specified in a schema import must not be xml or xmlns [err:XQST0070], and must not be the same as any namespace prefix bound in the same module by another schema import, a module import, a namespace declaration, or a module declaration [err:XQST0033].

Note:

If schema definitions from the xml namespace are to be used (for example, schema-attribute(xml:space), then the prolog should include a declaration in the form import schema "http://www.w3.org/XML/1998/namespace". No prefix should be supplied (the xml prefix is predeclared), and no location hint should be provided (the schema definitions for the namespace are built in, and cannot be varied).

If the schema import declaration specifies default element namespace then the prolog must not contain a namespace declaration that specifies default element namespace or default type namespace.

If the keyword "fixed", is present, the default namespace for elements and types is fixed throughout the module, and is not affected by default namespace declarations (xmlns="") appearing on direct element constructors.

The first URILiteral in a schema import specifies the target namespace of the schema to be imported.

If the target namespace is http://www.w3.org/2005/xpath-functions then the schema described in Section C SchemasFO is imported; any location hints are ignored.

A schema import that specifies a zero-length string as target namespace is considered to import a schema that has no target namespace. Such a schema import must not bind a namespace prefix [err:XQST0057], but it may set the default element and/or type namespace to a zero-length string (representing “no namespace”), thus enabling the definitions in the imported namespace to be referenced. If the default namespace for elements and types is not set to "no namespace", the only way to reference the definitions in an imported schema that has no target namespace is using the EQName syntax Q{}local-name.

The URILiterals that follow the at keyword are optional location hints, intended to allow a processor to locate schema documents containing definitions of the required schema components in the target namespace. Processors may interpret or disregard these hints in an implementation-defined way. The preferred strategy, which should be used by default unless the user indicates otherwise, is as follows:

  1. If the target namespace is one for which the processor has built-in knowledge, for example the schema for a reserved namespace, the location hints should be ignored, and the built-in schema used in preference.

  2. In other cases, the location hints are taken in order, treating them as URI references relative to the static base URI of the query module.

  3. If the first location hint cannot be successfully dereferenced, then that location hint is disregarded (optionally with a warning), and the process continues with the next location hint, until one is found that can be successfully dereferenced; if none of the location hints can be dereferenced, then a static error is reported.

  4. The dereferencing of a location hint may make use of implementation-defined indirection mechanisms such as resolver callbacks and catalog files.

  5. If a location hint is successfully dereferenced, but yields a resource that cannot be parsed as a valid XSD schema document with the correct target namespace, then a static error is reported.

  6. If a valid schema document is located, then it is combined with the schema documents obtained from other import schema declarations, in the same way as a schema is assembled from multiple schema documents referenced using xs:import declarations. This implies that the several schema documents must together comprise a valid schema, for example there cannot be two different type definitions with the same name.

  7. Once one location hint has been successfully processed, subsequent location hints are ignored.

Note:

Processors that adopted a different strategy in earlier releases may continue to use that strategy by default, in order to retain compatibility; however such processors should offer the above strategy as an option.

The process described above is not intended to be totally prescriptive, or to guarantee complete interoperability. Processors are likely to exhibit variations, depending both on design decisions made by the product vendor, and on decisions made when configuring the platform and network infrastructure on which it runs. For example, when retrieving HTTP resources, the details of the HTTP request are likely to vary, and the criteria used to decide whether a request was successful may also vary. In addition, the XSD specification itself describes some aspects of the process incompletely, including for example the criteria used to decide whether two components (such as type definitions) should be considered identical.

Different query modules may import different schemas, but there is a requirement that all the schemas used by a query must be compatible. The rules for compatibility are defined in Section 2.8.1 Schema ConsistencyDM. This means, for example:

  • If any schema component (such as an element declaration or complex type definition) is imported into more than one query module, the definitions of these components must effectively be the same.

  • This leaves room, however, for some differences between modules. For example, the substitution group membership of an element declaration may vary between one module and another, depending on what other element declarations are present in the schema. This means that an element can be validated in one module and passed as a function parameter to another module in which the element would be considered invalid. Any static type inferencing that is performed must take such possibilities into account; this is particularly important if query modules are compiled independently from one another.

If the target namespace is http://www.w3.org/2005/xpath-functions then the schema described in Section C Schemas FO31 is imported; any location hints are ignored.

It is a static error [err:XQST0058] if more than one schema import in the same Prolog specifies the same target namespace. It is a static error [err:XQST0059] if the implementation is not able to process a schema import by finding a valid schema with the specified target namespace.

It is a static error [err:XQST0012] if the set of definitions contained in all schemas imported by a Prolog do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema 1.0] or [XML Schema 1.1] Part 1: in particular, each definition must be valid, complete, and unique.

It is a static error [err:XQST0149] if the schemas imported by different modules of a query are not compatible as defined in Section 2.8.1 Schema ConsistencyDM.

The following example imports a schema, specifying both its target namespace and its location, and binding the prefix soap to the target namespace:

import schema namespace soap="http://www.w3.org/2003/05/soap-envelope" 
  at "http://www.w3.org/2003/05/soap-envelope/";

The following example imports a schema by specifying only its target namespace, and makes it the default namespace for elements and types:

import schema default element namespace "http://example.org/abc";

The following example imports a schema that has no target namespace, providing a location hint, and sets the default namespace for elements and types to “no namespace” so that the definitions in the imported schema can be referenced:

import schema default element namespace "" at "http://example.org/xyz.xsd";

The following example imports a schema that has no target namespace and sets the default namespace for elements and types to “no namespace”. Since no location hint is provided, it is up to the implementation to find the schema to be imported.

import schema default element namespace "";

5.12 Module Import

ModuleImport::="import" "module" ("namespace" NCName "=")? URILiteral ("at" (URILiteral ++ ","))?

[Definition: A module import imports the public variable declarations, public function declarations, and public item type declarations from one or more library modules into the statically known function definitions, in-scope variables, or in-scope named item types of the importing module.] Each module import names a target namespace and imports an implementation-defined set of modules that share this target namespace. The module import may bind a namespace prefix to the target namespace, adding the (prefix, URI) pair to the statically known namespaces, and it may provide optional hints for locating the modules to be imported.

If a module A imports module B, the static context of module A will contain the statically known function definitions, in-scope variables, or in-scope named item types of module B, and the dynamic context of module A will contain the public variable values and dynamically known function definitions of module B. It will not contain:

The following example illustrates a module import:

import module namespace gis="http://example.org/gis-functions";

If a query imports the same module via multiple paths, only one instance of the module is imported. Because only one instance of a module is imported, there is only one instance of each variable declared in a module's prolog.

A module may import its own target namespace (this is interpreted as importing an implementation-defined set of other modules that share its target namespace.)

The namespace prefix specified in a module import must not be xml or xmlns [err:XQST0070], and must not be the same as any namespace prefix bound in the same module by another module import, a schema import, a namespace declaration, or a module declaration with a different target namespace [err:XQST0033].

The first URILiteral in a module import must be of nonzero length [err:XQST0088], and specifies the target namespace of the modules to be imported. The URILiterals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an implementation-defined way.

It is a static error [err:XQST0047] if more than one module import in a Prolog specifies the same target namespace. It is a static error [err:XQST0059] if the implementation is not able to process a module import by finding a valid module definition with the specified target namespace. It is a static error if two or more variables declared or imported by a module have equal expanded QNames (as defined by the eq operator) [err:XQST0049].

Module imports are not transitive. Importing a module provides access only to declarations contained directly in the imported module. For example, if module A imports module B, and module B imports module C, module A does not have access to the functions and variables declared in module C.

Example: Schema Information and Module Import

A module import does not import schema definitions from the imported module. In the following query, the type geometry:triangle is not defined, even if it is known in the imported module, so the variable declaration raises an error [err:XPST0051]:

(: Error - geometry:triangle is not defined :) 
import module namespace geo = "http://example.org/geo-functions"; 
declare variable $triangle as geometry:triangle := geo:make-triangle(); 
$triangle

Without the type declaration for the variable, the variable declaration succeeds:

import module namespace geo = "http://example.org/geo-functions";
declare variable $triangle := geo:make-triangle();
$triangle

Importing the schema that defines the type of the variable, the variable declaration succeeds:

import schema namespace geometry = "http://example.org/geo-schema-declarations"; 
import module namespace geo = "http://example.org/geo-functions"; 
declare variable $triangle as geometry:triangle := geo:make-triangle();
$triangle

5.12.1 The Target Namespace of a Module

The target namespace of a module should be treated in the same way as other namespace URIs.

To maximize interoperability, query authors should use a string that is a valid absolute IRI.

Implementions must accept any string of Unicode characters. Target namespace URIs are compared using the Unicode codepoint collation rather than any concept of semantic equivalence.

Implementations may provide mechanisms allowing the target namespace URI to be used as input to a process that delivers the module as a resource, for example a catalog, module repository, or URI resolver. For interoperability, such mechanisms should not prevent the user from choosing an arbitrary URI for naming a module.

Similarly, implementations may perform syntactic transformations on the target namespace URI to obtain the names of related resources, for example to implement a convention relating the name or location of compiled code to the target namespace URI; but again, such mechanisms should not prevent the user from choosing an arbitrary target namespace URI.

As with other namespace URIs, it is common practice to use target namespace URIs whose scheme is http and whose authority part uses a DNS domain name under the control of the user.

The specifications allow, and some users might consider it good practice, for the target namespace URI of a function library to be the same as the namespace URI of the XML vocabulary manipulated by the functions in that library.

5.12.2 Multiple Modules with the same Namespace

Several different modules with the same target namespace can be used in the same query. The names of public variables and public functions must be unique within the static context of a query: this means that if two modules with the same target namespace URI are used in the same query, the names of the public variables and functions in their module contexts must not overlap.

If one module contains an import module declaration with the target namespace M, then all public variables and public functions in the contexts of modules whose target namespace is M must be accessible in the importing module, regardless whether the participation of the imported module was directly due to this "import module" declaration.

5.12.3 Location URIs

The term “location URIs” refers to the URIs in the at clause of an import module declaration.

Products should (by default or at user option) take account of all the location URIs in an import module declaration, treating each location URI as a reference to a module with the specified target namespace URI. Location URIs should be made absolute with respect to the static base URI of the module containing the import module declaration where they appear. The mapping from location URIs to module source code or compiled code MAY be done in any way convenient to the implementation. If possible given the product’s architecture, security requirements, etc, the product should allow this to fetch the source code of the module to use the standard web mechanisms for dereferencing URIs in standard schemes such as the http URI scheme.

When the same absolutized location URI is used more than once, either in the same import module declaration or in different import module declarations within the same query, a single copy of the resource containing the module is loaded. When different absolutized location URIs are used, each results in a single module being loaded, unless the implementation is able to determine that the different URIs are references to the same resource. No error due to duplicate variable or functions names should arise from the same module being imported more than once, so long as the absolute location URI is the same in each case.

Implementations must report a static error if a location URI cannot be resolved after all available recovery strategies have been exhausted.

5.12.4 Cycles

Implementations must resolve cycles in the import graph, either at the level of target namespace URIs or at the level of location URIs, and ensure that each module is imported only once.

5.13 Namespace Declaration

Changes in 4.0  

  1. All implementations must now predeclare the namespace prefixes math, map, array, and err. In XQuery 3.1 it was permitted but not required to predeclare these namespaces.

NamespaceDecl::="declare" "namespace" NCName "=" URILiteral

[Definition: A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.] The namespace declaration is in scope throughout the query in which it is declared, unless it is overridden by a namespace declaration attribute in a direct element constructor.

If the URILiteral part of a namespace declaration is a zero-length string, any existing namespace binding for the given prefix is removed from the statically known namespaces. This feature provides a way to remove predeclared namespace prefixes such as local.

The following query illustrates a namespace declaration:

declare namespace foo = "http://example.org";
<foo:bar> Lentils </foo:bar>

In the query result, the newly created node is in the namespace associated with the namespace URI http://example.org.

The namespace prefix specified in a namespace declaration must not be xml or xmlns [err:XQST0070]. The namespace URI specified in a namespace declaration must not be http://www.w3.org/XML/1998/namespace or http://www.w3.org/2000/xmlns/ [err:XQST0070]. The namespace prefix specified in a namespace declaration must not be the same as any namespace prefix bound in the same module by a module import, schema import, module declaration, or another namespace declaration [err:XQST0033].

It is a static error [err:XPST0081] if an expression contains a lexical QName with a namespace prefix that is not in the statically known namespaces.

XQuery has several predeclared namespace prefixes, which are listed in 2.1.3 Namespaces and QNames. These prefixes may be used without an explicit declaration; they are present in the statically known namespaces before each query is processed. They may be overridden by namespace declarations in a Prolog or by namespace declaration attributes on constructed elements (however, the prefix xml must not be redeclared, and no other prefix may be bound to the namespace URI associated with the prefix xml [err:XQST0070]).

Additional predeclared namespace prefixes may be added to the statically known namespaces by an implementation.

When element or attribute names are compared, they are considered identical if the local parts and namespace URIs match on a codepoint basis. Namespace prefixes need not be identical for two names to match, as illustrated by the following example:

declare namespace xx = "http://example.org";

let $node := <foo:bar xmlns:foo = "http://example.org">
  <foo:bing> Lentils </foo:bing>
</foo:bar>
return $node/xx:bing

Although the namespace prefixes xx and foo differ, both are bound to the namespace URI http://example.org. Since xx:bing and foo:bing have the same local name and the same namespace URI, they match. The output of the above query is as follows.

<foo:bing xmlns:foo="http://example.org"> Lentils </foo:bing>

5.14 Default Namespace Declaration

Changes in 4.0  

  1. The default namespace for elements and types can now be declared to be fixed for a query module, meaning it is unaffected by a namespace declaration appearing on a direct element constructor.   [Issue 65 PR 753 31 October 2023]

  2. The default namespace for elements and types can be set to the value ##any, allowing unprefixed names in axis steps to match elements with a given local name in any namespace.   [Issue 296 PR 1181 30 April 2023]

DefaultNamespaceDecl::="declare" "fixed"? "default" ("element" | "function") "namespace" URILiteral

Default namespace declarations can be used in a Prolog to facilitate the use of unprefixed QNames.

The namespace URI specified in a default namespace declaration must not be http://www.w3.org/XML/1998/namespace or http://www.w3.org/2000/xmlns/ [err:XQST0070].

The following kinds of default namespace declarations are supported:

  • A default element namespace declaration declares how unprefixed element and type names are to be interpreted. The relevant value is recorded as the default namespace for elements and types in the static context for the query module. A Prolog may contain at most one default element namespace declaration and it must not contain both a default element namespace declaration and an import schema declaration that specifies a default element namespace [err:XQST0066].

    The URILiteral may take one of the following forms:

    • A namespace URI. This namespace will be used for all unprefixed names appearing where an element or type name is expected.

    • The empty string "". In this case unprefixed names appearing where an element or type name is expected are treated as being in no namespace: the default namespace for elements and types is set to absentDM.

    • The string "##any". In this case an unprefixed name appearing as a NameTest in an axis step whose principal node kind is element is interpreted as a wildcard (the unprefixed name N is treated as equivalent to the wildcard *:N); an unprefixed name used appearing where an item type name is expected is interpreted as a local name in namespace http://www.w3.org/2001/XMLSchema, while an unprefixed name appearing in any other context where an element or type name is expected is treated as being in no namespace.

      Note:

      To take an example, older versions of the internet index of RFCs (requests for comments) use the namespace URI http://www.rfc-editor.org/rfc-index, while newer versions use https://www.rfc-editor.org/rfc-index (note the change of URI scheme). XPath code that needs to work with either version can be simplified by setting the default namespace to ##any: but be aware that this might lead to spurious matching of names in an unrelated namespace.

    The following example illustrates the declaration of a default namespace for elements and types:

    declare default element namespace "http://example.org/names";

    If no default element namespace declaration is present, unprefixed element and type names are in no namespace (however, an implementation may define a different default as specified in C.1 Static Context Components.)

    If the keyword "fixed", is present, the default namespace for elements and types is fixed throughout the module, and is not affected by default namespace declarations (xmlns="") appearing on direct element constructors.

  • A default function namespace declaration declares a namespace URI that is associated with unprefixed function names in static function calls and function declarations.

    A Prolog may contain at most one default function namespace declaration [err:XQST0066]. If the StringLiteral in a default function namespace declaration is a zero-length string, the default function namespace is undeclared (set to absentDM). In that case, any functions that are associated with a namespace can be called only by using an explicit namespace prefix.

    If no default function namespace declaration is present, the default function namespace is the namespace of XPath/XQuery functions, http://www.w3.org/2005/xpath-functions (however, an implementation may define a different default as specified in C.1 Static Context Components.)

    The following example illustrates the declaration of a default function namespace:

    declare default function namespace "http://www.w3.org/2005/xpath-functions/math";

    The effect of declaring a default function namespace is that all functions in the default function namespace, including implicitly declared constructor functions, can be invoked without specifying a namespace prefix. When a static function call uses a function name with no prefix, the local name of the function must match a function (including implicitly declared constructor functions) in the default function namespace [err:XPST0017].

    Note:

    Only constructor functions can be in no namespace.

    The keyword "fixed" has no effect when declaring a default function namespace, since there is no mechanism to change the default function namespace within a query module.

Unprefixed attribute names and variable names are in no namespace.

5.15 Annotations

AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
InlineFunctionExpr::=Annotation* ("function" | "fn") FunctionSignature? FunctionBody
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
AnnotationValue::=StringLiteral | ("-"? NumericLiteral) | ("true" "(" ")") | ("false" "(" ")")

XQuery uses annotations to declare properties associated with functions (inline or declared in the prolog) and variables. For instance, a function may be declared %public or %private. The semantics associated with these properties are described in 5.18 Function Declarations.

Annotations are (QName, value) pairs. If the EQName of the annotation is a lexical QName, the prefix of the QName is resolved using the statically known namespaces; if no prefix is present, the name is in the http://www.w3.org/2012/xquery namespace.

Note:

The default namespace is a reserved namespace, which means that unprefixed names cannot be used for implementation-defined or user-defined annotations. It is permitted to use a no-namespace name, which might be written, for example, as %Q{}inline; however, this is discouraged because it is likely to reduce portability across implementations.

In general there is no rule preventing two annotations on the same declaration having the same name, although this is disallowed for some specific annotations such as %public and %private. The order of annotations may be significant.

If there is no value associated with an annotation, the effective value is the empty sequence. This is the case, for example, with the annotations %public and %private.

A few annotations, such as %public and %private, have rules defined by this specification. Implementations may define further annotations, whose behavior is implementation-defined. For instance, if the eg prefix is bound to a namespace recognized by a particular implementation, then it could be used to define an annotation like eg:sequential. If the namespace URI of an annotation is not recognized by the implementation, then the annotation has no effect, other than being available for inspection using the fn:function-annotations function.

Implementations may also provide a way for users to define their own annotations. Implementations must not define annotations, or allow users to define annotations, in reserved namespaces; it is a static error [err:XQST0045] for the name of an annotation to be in a reserved namespace.

An annotation can provide values explicitly using a parenthesized list of constant values. These values may take any of the following forms:

  • A string literal, for example "Paris" or 'London', denoting a value of type xs:string.

  • A numeric literal, for example 0, 0.1, 0x7FFF, or 1e-6, denoting a value of type xs:decimal, xs:integer, or xs:double. The literal may be preceded by a minus sign to represent a negative number.

  • One of the constructs true() or false(), denoting the xs:boolean values true and false respectively.

For example, the annotation %java:method("java.lang.Math.sin") sets the value of the java:method annotation to the string value java.lang.Math.sin. An implementation might define such annotations to facilitate calling external functions.

Note:

The constructs true() and false() must be written as prescribed by the grammar. No namespace prefix is allowed. Although the values resemble calls to functions in the default function namespace, they are unaffected by the namespace context.

5.16 Variable Declaration

Changes in 4.0  

  1. The coercion rules are now used when binding values to variables (both global variable declarations and local variable bindings). This aligns XQuery with XSLT, and means that the rules for binding to variables are the same as the rules for binding to function parameters.   [Issue 189 PR 254 29 November 2022]

  2. In earlier versions, the static context for the initializing expression excluded the variable being declared. This restriction has been lifted.   [Issue 1379 PR 1432 12 September 2024]

AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
VarDecl::="variable" VarNameAndType ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
VarNameAndType::="$" EQNameTypeDeclaration?
VarName::="$" EQName
TypeDeclaration::="as" SequenceType
VarValue::=ExprSingle
VarDefaultValue::=ExprSingle

[Definition: A variable declaration in the XQuery prolog defines the name and static type of a variable, and optionally a value for the variable. It adds to the in-scope variables in the static context, and may also add to the variable values in the dynamic context.]

Note:

The term variable declaration always refers to a declaration of a variable in a Prolog. The binding of a variable to a value in a query expression, such as a FLWOR expression, is known as a variable binding, and does not make the variable visible to an importing module.

During static analysis, a variable declaration causes a pair (expanded QName N, type T) to be added to the in-scope variables. The expanded QName N is the VarName. If N is equal (as defined by the eq operator) to the expanded QName of another variable in in-scope variables, a static error is raised [err:XQST0049]. The type T of the declared variable is as follows:

  • If TypeDeclaration is present, then the SequenceType in the TypeDeclaration; otherwise

  • Otherwise, item()*.

All variable names declared in a library module must (when expanded) be in the target namespace of the library module [err:XQST0048]. A variable declaration may use annotations to specify that the variable is %private or %public (which is the default). [Definition: A private variable is a variable with a %private annotation. A private variable is hidden from module import, which can not import it into the in-scope variables of another module.] [Definition: A public variable is a variable without a %private annotation. A public variable is accessible to module import, which can import it into the in-scope variables of another module. Using %public and %private annotations in a main module is not an error, but it does not affect module imports, since a main module cannot be imported. It is a static error [err:XQST0116] if a variable declaration contains both a %private and a %public annotation, more than one %private annotation, or more than one %public annotation.]

Variable names that have no namespace prefix are in no namespace. Variable declarations that have no namespace prefix may appear only in a main module.

Here are some examples of variable declarations:

  • The following declaration specifies both the type and the value of a variable. This declaration causes the type xs:integer to be associated with variable $x in the static context, and the value 7 to be associated with variable $x in the dynamic context.

    declare variable $x as xs:integer := 7;
  • The following declaration specifies a value but not a type. The static type of the variable is inferred from the static type of its value. In this case, the variable $x has a static type of xs:decimal, inferred from its value which is 7.5.

    declare variable $x := 7.5;
  • The following declaration specifies a type but not a value. The keyword external indicates that the value of the variable will be provided by the external environment. At evaluation time, if the variable $x in the dynamic context does not have a value of type xs:integer, a type error is raised.

    declare variable $x as xs:integer external;
  • The following declaration specifies neither a type nor a value. It simply declares that the query depends on the existence of a variable named $x, whose type and value will be provided by the external environment. During query analysis, the type of $x is considered to be item()*. During query evaluation, the dynamic context must include a type and a value for $x, and its value must be compatible with its type.

    declare variable $x external;
  • The following declaration, which might appear in a library module, declares a variable whose name includes a namespace prefix:

    declare variable $sasl:username as xs:string := "jonathan@example.com";
  • This is an example of an external variable declaration that provides a VarDefaultValue:

    declare variable $x as xs:integer external := 47;

An implementation can provide annotations it needs. For instance, an implementation that supports volatile external variables might allow them to be declared using an annotation:

declare %eg:volatile variable $time as xs:time external;

[Definition: If a variable declaration includes an expression (VarValue or VarDefaultValue), the expression is called an initializing expression. The static context for an initializing expression includes all functions, variables, and namespaces that are declared or imported anywhere in the Prolog.]

If a required type is defined, then the value obtained by evaluating the initializing expression is converted to the required type by applying the coercion rules. A type error occurs if this is not possible. In invoking the coercion rules, XPath 1.0 compatibility mode does not apply.

In a module's dynamic context, a variable value (or the context value) may depend on another variable value (or the context value). [Definition: A variable value (or the context value) depends on another variable value (or the context value) if, during the evaluation of the initializing expression of the former, the latter is accessed through the module context.]

In the following example, the value of variable $adepends on the value of variable $b because the evaluation of $a's initializing expression accesses the value of $b during the evaluation of local:f().

declare variable $a := local:f(); 
declare variable $b := 1;
declare function local:f() { $b };

A directed graph can be built with all variable values and the context value as nodes, and with the depend on relation as edges. This graph must not contain cycles, as it makes the population of the dynamic context impossible. If it is discovered, during static analysis or during dynamic evaluation, that such a cycle exists, error [err:XQDY0054] must be raised.

During query evaluation, each variable declaration causes a pair (expanded QName N, value V) to be added to the variable values. The expanded QName N is the VarName. The value V is as follows:

  • If VarValue is specified, then V is the result of evaluating VarValue.

  • If external is specified, then:

    • if a value is provided for the variable by the external environment, then V is that value. The means by which typed values of external variables are provided by the external environment is implementation-defined.

    • if no value is provided for the variable by the external environment, and VarDefaultValue is specified, then V is the result of evaluating VarDefaultValue.

    • If no value is provided for the variable by the external environment, and VarDefaultValue is not specified, then a dynamic error is raised [err:XPDY0002].

      It is implementation-dependent whether this error is raised if the evaluation of the query does not reference the value of the variable.

In all cases the value V must match the type T according to the rules for SequenceType matching; otherwise a type error is raised [err:XPTY0004].

5.17 Context Value Declaration

Changes in 4.0  

  1. The concept of the context item has been generalized, so it is now a context value. That is, it is no longer constrained to be a single item.   [Issue 129 PR 368 21 July 2023]

ContextValueDecl::="declare" "context" (("value" ("as" SequenceType)?) | ("item" ("as" ItemType)?)) ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))

A context value declaration allows a query to specify the static type, value, or default value for the initial context value.

Only the main module can set the initial context value. In a library module, a context value declaration must be external, and specifies only the static type. Specifying a VarValue or VarDefaultValue for a context value declaration in a library module is a static error [err:XQST0113].

The form declare context value allows the initial context value to set to any value, with any sequence type. The alternative form declare context item is retained for compatibility with earlier versions of XQuery, and requires the value to be a single item, and the type (if specified) to be an item type.

In every module that does not contain a context value declaration, the effect is as if the declaration

declare context value as item()* external;

appeared in that module.

The context value declaration has the effect of setting the context value static type T in the static context. When the form declare context value is used, the default type is item()*. When the alternative form declare context item is used, the default type is item().

If a module contains more than one context value declaration, a static error is raised [err:XQST0099].

The static context for an initializing expression includes all functions, variables, and namespaces that are declared or imported anywhere in the Prolog.

During query evaluation, a fixed focus is created in the dynamic context for the evaluation of the QueryBody in the main module, and for the initializing expression of every variable declaration in every module. The context value of this fixed focus is called the initial context value, which is selected as follows:

  • If VarValue is specified, then the initial context value is the result of evaluating VarValue.

    Note:

    In such a case, the initial context value does not obtain its value from the external environment. If the external environment attempts to provide a value for the initial context value, it is outside the scope of this specification whether that is ignored, or results in an error.

  • If external is specified, then:

    • If the declaration occurs in a main module and a value is provided for the context value by the external environment, then the initial context value is that value.

      Note:

      If the declaration occurs in a library module, then it does not set the value of the initial context value, the value is set by the main module.

      The means by which an external value is provided by the external environment is implementation-defined.

    • If no value is provided for the context value by the external environment, and VarDefaultValue is specified, then the initial context value is the result of evaluating VarDefaultValue as described below.

In all cases where the context value has a value, that value must match the type T according to the rules for SequenceType matching; otherwise a type error is raised [err:XPTY0004]. If more than one module contains a context value declaration, the context value must match the type declared in each one.

If VarValue or VarDefaultValue is evaluated, the static and dynamic contexts for the evaluation are the current module's static and dynamic context.

If a required type is defined, then the value obtained by evaluating VarValue or VarDefaultValue is converted to the required type by applying the coercion rules. A type error occurs if this is not possible. In invoking the coercion rules, XPath 1.0 compatibility mode does not apply.

Here are some examples of context value declarations.

  • Declare the type of the context value as a single element item with a required element name:

    declare namespace env = "http://www.w3.org/2003/05/soap-envelope"; 
    declare context item as element(env:Envelope) external;
  • Declare a default context value, which is a system log in a default location. If the system log is in a different location, it can be specified in the external environment:

    declare context value as element(sys:log) external :=
      doc("/var/xlogs/sysevent.xml")/sys:log;
  • Declare a context value, which is collection whose collection URI is supplied as an external parameter to the query. If the system log is in a different location, it can be specified in the external environment:

    declare variable $uri as xs:string external;
    declare context value as document-node()* := collection($uri);

    With this declaration, a query body such as //person[name="Mandela"] returns all matching person elements appearing in any document in the collection.

5.18 Function Declarations

Changes in 4.0  

  1. Function definitions in the static context may now have optional parameters, provided this does not cause ambiguity across multiple function definitions with the same name. Optional parameters are given a default value, which can be any expression, including one that depends on the context of the caller (so an argument can default to the context value).

In addition to the system functions, XQuery allows users to declare functions of their own. A function declaration declares a family of functions having the same name and similar parameters. The declaration specifies the name of the function, the names and datatypes of the parameters, and the datatype of the result. All datatypes are specified using the syntax described in 3 Types.

Including a function declaration in the query causes a corresponding function definition to be added to the statically known function definitions of the static context. The associated functions also become available in the dynamically known function definitions of the dynamic context.

AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
FunctionDecl::="function" EQName "(" ParamListWithDefaults? ")" TypeDeclaration? (FunctionBody | "external")
/* xgc: reserved-function-names */
ParamListWithDefaults::=(ParamWithDefault ++ ",")
ParamWithDefault::=VarNameAndType (":=" ExprSingle)?
FunctionBody::=EnclosedExpr
TypeDeclaration::="as" SequenceType
EnclosedExpr::="{" Expr? "}"

A function declaration specifies whether the implementation of the function is user-defined or external.

In addition to user-defined functions and external functions, XQuery 4.0 allows anonymous functions to be declared in the body of a query using inline function expressions.

The following example illustrates the declaration and use of a local function that accepts a sequence of employee elements, summarizes them by department, and returns a sequence of dept elements.

Example: Using a function, prepare a summary of employees that are located in Denver.
declare function local:summary($emps as element(employee)*) as element(dept)* { 
  for $no in distinct-values($emps/deptno) 
  let $emp := $emps[deptno = $no]
  return <dept> 
    <deptno>{ $no }</deptno> 
    <headcount>{ count($emp) }</headcount> 
    <payroll>{ sum($emp/salary) }</payroll> 
  </dept> 
};
local:summary(doc("acme_corp.xml")//employee[location = "Denver"])

5.18.1 User-Defined Functions

[Definition: User defined functions are functions that contain a function body, which provides the implementation of the function as a content expression.] The static context for a function body includes all functions, variables, and namespaces that are declared or imported anywhere in the Prolog, including the function being declared. Its in-scope variables component also includes the parameters of the function being declared.

An implementation should raise a static error [err:XPST0008] if the function body depends on the context value.

The properties of the function definitionF are derived from the syntax of the function declaration as follows:

  • The name of F is the expanded QName obtained by expanding the EQName that follows the keyword function.

  • The parameters of F are derived from the ParamWithDefault entries in the ParamListWithDefaults:

    • The parameter name is the expanded QName obtained by expanding the EQName that follows the $ symbol.

    • The required type of the parameter is given by the TypeDeclaration, defaulting to item()*.

    • The default value of the parameter is given by the expression that follows the := symbol; if there is no default value, then the parameter is a required parameter.

  • The return type of the function is given by the final TypeDeclaration that follows the ParamListWithDefaults if present, defaulting to item()*.

  • The function annotations are derived from the annotations that follow the % symbol, if present.

  • The implementation of the function is given by the enclosed expression.

The static context may include more than one declared function with the same name, but their arity ranges must not overlap [err:XQST0034].

Note:

A consequence of this rule is that a function declaration must not declare a function that has arity 1 (one) if its name is the same as the name of an imported atomic type, since the name would then clash with the constructor function for that type.

5.18.2 Function Names

Every declared function must be in a namespace; that is, every declared function name must (when expanded) have a non-null namespace URI [err:XQST0060]. If the function name in a function declaration has no namespace prefix, it is considered to be in the default function namespace. Every function name declared in a library module must (when expanded) be in the target namespace of the library module [err:XQST0048].

[Definition: A reserved namespace is a namespace that must not be used in the name of a function declaration.] It is a static error [err:XQST0045] if the function name in a function declaration (when expanded) is in a reserved namespace. The following namespaces are reserved namespaces:

  • http://www.w3.org/XML/1998/namespace

  • http://www.w3.org/2001/XMLSchema

  • http://www.w3.org/2001/XMLSchema-instance

  • http://www.w3.org/2005/xpath-functions

  • http://www.w3.org/2005/xpath-functions/array

  • http://www.w3.org/2005/xpath-functions/map

  • http://www.w3.org/2005/xpath-functions/math

  • http://www.w3.org/2012/xquery

In order to allow main modules to declare functions for local use within the module without defining a new namespace, XQuery predefines the namespace prefix local to the namespace http://www.w3.org/2005/xquery-local-functions. It is suggested (but not required) that this namespace be used for defining local functions.

5.18.3 Function Parameters

The function declaration includes a list of zero or more function parameters.

The parameters of a function declaration are considered to be variables whose scope is the function body. It is an static error [err:XQST0039] for a function declaration to have more than one parameter with the same name. The type of a function parameter can be any type that can be expressed as a sequence type.

If a function parameter is declared using a name but no type, its default type is item()*. If the result type is omitted from a function declaration, its default result type is item()*.

The function body defines the implementation of the function definition. The rules for static function calls (see 4.5.1.2 Evaluating Static Function Calls) ensure that a value is available for each parameter, whether required or optional, and that the value will always be an instance of the declared type.

A parameter is optional if a default value is supplied using the construct := ExprSingle; otherwise it is required. If a parameter is optional, then all subsequent parameters in the list must also be optional; otherwise, a static error is raised [err:XQST0148]. In other words, the parameter list includes zero or more required parameters followed by zero or more optional parameters.

The number of arguments that may be supplied in a call to this family of functions is thus in the range M to N, where M is the number of required parameters, and N is the total number of parameters (whether required or optional). This is refered to as the arity range of the function definition.

The default value for an optional parameter will often be supplied using a simple literal or constant expression, for example $married as xs:boolean := false() or $options as map(*) := { }. However, to allow greater flexibility, the initial value can also be context-dependent. For example, $node as node() := . declares a parameter whose default value is the context value from the dynamic context of the caller, while $collation as xs:string := default-collation() declares a parameter whose default value is the default collation from the dynamic context of the caller. The detailed rules are as follows. In these rules, the term caller means the function call or function reference that invokes the function being defined.

The static context for the initializing expression of an optional parameter is the same as the static context for the initializing expression of a variable declaration (see 5.16 Variable Declaration), with the following exceptions:

  • The in-scope variables component is empty. This means that the initializing expression cannot refer to any variables, other than local variables declared within the expression itself. Note in particular that it cannot refer to other parameters of the function.

  • The statically known function definitions excludes all user-defined functions.

The dynamic context for the initializing expression of an optional parameter is the same as the dynamic context of the caller, with the following exceptions:

5.18.4 Function Annotations

Changes in 4.0  

  1. The values true() and false() are allowed in function annotations, and negated numeric literals are also allowed.   [Issue 637 PR 682 12 September 2023]

A function declaration may use the %private or %public annotations to specify that a function is public or private; if neither of these annotations is used, the function is public. [Definition: A private function is a function with a %private annotation. A private function is hidden from module import, which can not import it into the statically known function definitions of another module. ] [Definition: A public function is a function without a %private annotation. A public function is accessible to module import, which can import it into the statically known function definitions of another module. ] Using %public and %private annotations in a main module is not an error, but it does not affect module imports, since a main module cannot be imported. It is a static error [err:XQST0106] if a function declaration contains both a %private and a %public annotation, more than one %private annotation, or more than one %public annotation.

An implementation can define annotations, in its own namespace, to support functionality beyond the scope of this specification. For instance, an implementation that supports external Java functions might use an annotation to associate a Java function with an XQuery external function:

declare 
  %java:method("java.lang.StrictMath.copySign") 
function smath:copySign($magnitude, $sign) external;

5.18.5 External Functions

In function declarations, external functions are identified by the keyword external. The purpose of a function declaration for an external function is to declare the datatypes of the function parameters and result, for use in type checking of the query that contains or imports the function declaration.

An XQuery implementation may provide a facility whereby external functions can be implemented, but it is not required to do so. If such a facility is provided, the protocols by which parameters are passed to an external function, and the result of the function is returned to the invoking query, are implementation-defined. An XQuery implementation may augment the type system of [XQuery and XPath Data Model (XDM) 4.0] with additional types that are designed to facilitate exchange of data, or it may provide mechanism for the user to define such types. For example, a type might be provided that encapsulates an object returned by an external function, such as an SQL database connection. These additional types, if defined, are considered to be derived by restriction from xs:anyAtomicType.

5.18.6 Recursion

A function declaration may be recursive—that is, it may reference itself. Mutually recursive functions, whose bodies reference each other, are also allowed.

Example: A recursive function to compute the maximum depth of a document

The following example declares a recursive function that computes the maximum depth of a node hierarchy, and calls the function to find the maximum depth of a particular document. The function local:depth calls the built-in functions empty and max, which are in the default function namespace.

declare function local:depth($e as node()) as xs:integer {
  (: A node with no children has depth 1 :)
  (: Otherwise, add 1 to max depth of children :)
  if (empty($e/*)) 
  then 1
  else max(for $c in $e/* return local:depth($c)) + 1
};

local:depth(doc("partlist.xml"))

[TODO: add an example of a function with an optional parameter.]

5.19 Item Type Declarations

An item type declaration defines a name for an item type. Defining a name for an item type allows it to be referenced by name rather than repeating the item type designator in full.

AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
ItemTypeDecl::="type" EQName "as" ItemType

An item type declaration adds a named item type to the in-scope named item types of the containing module. This enables the item type to be referred to using a simple name.

For example, given the declaration:

declare type app:invoice as map("xs:string", element(inv:paid-invoice));

It becomes possible to declare a variable containing a sequence of such items as:

declare variable $invoices as app:invoice*;

The definition can also be used within another item type declaration:

declare type app:overdue-invoices as map("xs:date", app:invoice*);

If the name of the item type being declared is written as an (unprefixed) NCName, then it is interpreted as being in the default namespace for elements and types.

An item type declaration may use the %private or %public annotations to specify that an item type name is public or private; if neither of these annotations is used, the declaration is public.

The declaration of an item type (whether locally declared in a module or imported from a public declaration in an imported module) must precede any use of the item type name: that is, the name only becomes available in the static context of constructs that lexically follow the relevant item type declaration or module import. A consequence of this rule is that cyclic and self-referential definitions are not allowed.

The name of an item type must be unique among the names of all declared item types and generalized atomic types in the static context of the query module. [err:XQST0146]

Note:

Named item types have been designed so that a reference to an item type name can be expanded (that is, replaced by its definition) as soon as the reference is encountered during query parsing. There is never any need to retain item type names at execution time except optionally for diagnostics.

Note:

It is possible to import a public variable or function into a different module even if its declaration refers to named item types that are not themselves imported (because they are declared as %private). This is because the type name can always be replaced by its definition. However, it is generally more convenient if any named item types used in public function and variable declarations are themselves public.

5.20 Named Record Types

Although item type declarations, as described in 5.19 Item Type Declarations, can be used to give names to record types as well as any other item type, named record types as described in this section provide a more concise syntax, plus additional functionality. In particular:

  • Named record types can be recursive.

  • Named record types implicitly create a constructor function that can be used to create instances of the record type.

  • A field in a named record type can be a function that has implicit access to the record on which it is defined, rather like methods in object-oriented languages.

The syntax is as follows:

AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
NamedRecordTypeDecl::="record" EQName "(" (ExtendedFieldDeclaration ** ",") ExtensibleFlag? ")"
ExtendedFieldDeclaration::=FieldDeclaration (":=" ExprSingle)?
FieldDeclaration::=FieldName "?"? ("as" SequenceType)?
FieldName::=NCName | StringLiteral

A named record declaration serves as both a named item type and as a function definition, and it therefore inherits rules from both these roles. In particular:

  1. Its name must not be the same as the name of any other named item type, or any generalized atomic type, that is present in the same static context [err:XQST0048].

  2. If the declaration appears within a library module then its name must be in the target namespace of the library module [err:XQST0048].

  3. As a function, it must not have an arity range that overlaps the arity range of any other function declaration having the same name in the same static context.

  4. The order of field declarations is significant, because it determines the order of arguments in a call to the constructor function.

  5. The fields must have distinct names. [err:XPST0021]

  6. In order to work as both a record type and a function declaration, the names of the fields must be simple NCNames in no namespace; the names must not be written as string literals [err:XPST0003].

    Note:

    This is described here as a semantic constraint, but an implementation might choose to impose it at the level of the grammar.

  7. If an initializing expression is present in an ExtendedFieldDeclaration, it must follow the rules for the initializing expression of a parameter in a function declaration, given in 5.18.3 Function Parameters. In particular, if any field has an initializing expression then all following fields must have an initializing expression.

  8. Any annotations that are present, such as %public or %private, apply both to the item type declaration and to the function declaration.

5.20.1 Named Records as Item Types

As a named item type declaration, the construct:

declare record cx:complex(r as xs:double, i as xs:double := 0);

is equivalent to:

declare type cx:complex as record(r as xs:double, i as xs:double);

Any initializing expressions for fields are ignored for this purpose.

Note:

The initializing expression only provides a default for values constructed using the constructor function. It has no effect on the rules for determining whether a particular value is a valid instance of the type, and it does not affect the result of retrieval operations such as the lookup operator.

There is however one significant difference: the name of a named record declaration is available throughout the static context of the module in which it is declared, including within the record declaration itself. This means that named record declarations can be self-recursive or mutually recursive.

Note:

Unlike a named item type declared using declare type, a reference to a named record type cannot (in general) be directly replaced by the corresponding record definition during parsing. This is not only because forwards references are allowed; it is also because a recursive record type cannot be expressed using the usual RecordType syntax.

A recursive record type will only be instantiable if every field whose value may contain instances of the record type (directly or indirectly) is optional or emptiable. Specifically, it must either be an optional field, or its type declaration must be such that it can hold an empty sequence or a value of a different type. A recursive record type that is not instantiable is considered to be implausible, which means that a processor may treat it as an error but is not obliged to do so [err:XPST0023].

5.20.2 Constructor Functions for Named Record Types

The construct:

declare record cx:complex(r as xs:double, i as xs:double := 0);

implicitly defines the function:

declare function cx:complex($r as xs:double, $i as xs:double := 0) as cx:complex {
  map:merge((
    { "r": $r },
    { "i": $i }
  ))
};

So the call cx:complex(3, 2) produces the value { "r": 3e0, "i": 2e0 }, while the call cx:complex(3) produces the value { "r": 3e0, "i": 0e0 }

If a field is declared as optional, by including a question mark after the name, and if it has no initializer, then the initializer := () is added implicitly. If the declared type of an optional field does not permit an empty sequence, then the declared type of the function parameter is adjusted by changing the occurrence indicator (from absent to ? or from + to *) in order to make the empty sequence an acceptable value.

Furthermore, if a field is optional and has no explicit initializer, the relevant entry in the constructed map will be absent when the value supplied (implicitly or explicitly) to the function argument is an empty sequence. This is achieved by modifying the function body. Given the declaration:

declare record cx:complex(r as xs:double, i? as xs:double);

the equivalent function declaration is:

declare function cx:complex($r as xs:double, $i as xs:double? := ()) as cx:complex {
  map:merge((
    { "r": $r },
    if (exists($i)) { { "i": $i } }
  ))
};

If any field is either declared optional, or has an explicit initializer, then all subsequent fields must also either be declared optional, or have an explicit initializer [err:XQST0148].

If the record type is declared as extensible (by the presence of a final ,*), then an additional paremeter is added to the function declaration. The name of the parameter is options (provided this name is available for use), its declared type is map(*), and its default value is {} (an empty map). The function body is then modified as shown in the following example. Given the declaration:

declare record p:person($first as xs:string, $last as xs:string, *);

the equivalent function declaration is:

declare function p:person(
  $first   as xs:string, 
  $last    as xs:string, 
  $options as map(*) := {}
) as p:person {
  map:merge((
    { "first": $first },
    { "last": $last },
    $options
  ),
  { "duplicates": "use-first" }
 };

The effect of the duplicates option here is that when two values are supplied for the same field, one as a direct argument in the function call and the other in the options map, the value supplied as a direct argument is used in preference.

If the name options is already in use for one of the fields, then the first available name from the sequence ("options1", "options2", ...) is used instead for the additional function parameter.

More formally, the equivalent function declaration is derived as follows:

  • The function annotations are the annotations on the named record declaration.

  • The function name is the QName of the named record declaration: an unprefixed name is expanded using the default namespace for elements and types. The resulting QName must be the same as the module namespace if the declaration appears in a library module, and in any event, it must be in some namespace.

  • The parameters of the function declaration are derived from the fields of the named record declaration, in order.

    • The name of the parameter is the name of the field (always an NCName).

    • The declared type of the parameter is the declared type of the field, if present; but if the field is optional, indicated by a question mark (?) after its name, and has no initializer, then the occurrence indicator is adjusted to permit an empty sequence, as described earlier.

    • The default value for the parameter is given by the initializing expression in the ExtendedFieldDeclaration, if present. If the field is optional and has no initializer, then it is given a default value of (), the empty sequence.

  • If the record type is extensible, then a further parameter is added at the end:

    • The name of the parameter is the first available name from the sequence ("options", "options1", "options2", ...).

    • The declared type of the parameter is map(*).

    • The default value of the parameter is {}, the empty map.

  • The return type of the function is the name of the record declaration, with no occurrence indicator.

  • The body of the function is a call of the function map:merge with two arguments:

    • The first argument is a parenthesized expression containing a comma-separated sequence of subexpressions, containing one subexpression for each field, in order, and optionally a further subexpression for the options parameter if present.

    • By default, the relevant subexpression is the map constructor { "N": $N } where N is the field name.

    • If the field is optional and is declared without an explicit initializer, then the relevant subexpression takes the form if (exists($N)) { { "N": $N } } where N is the field name.

    • The optional final subexpression, if present, takes the form $options, where $options is the name allocated to the final parameter.

    • The second argument in the call of the function map:merge is the map { "duplicates": "use-first" }. This can be omitted if the record is not extensible, because in this case duplicate field names cannot arise.

Note that a question mark ? after the field name indicates that the field is optional from the point of view of conformance of an item to the record type. The presence of an initializer indicates that it is optional from the point of view of a call on the constructor function. The two things are independent of each other. For example:

  • record(longitude, latitude, altitude?)

    Defines a record type in which altitude entry may be absent, and a constructor function with three arguments, of which the last is optional; if the function is called with two arguments (or with the third argument set to an empty sequence), then there will be no altitude entry in the resulting map.

    record(longitude, latitude, altitude := 0)

    Defines a record type in which all three fields will always be present, and a constructor function in which the third argument can be omitted, defaulting to zero.

    record(longitude, latitude, altitude? := ())

    Defines a record type in which the altitude entry may be absent both from the record and in the function call: but because a default value has been supplied explicitly, the constructed map will always have an entry for altitude.

5.20.3 Using Functions as Entries in Records

Named record declarations are useful in conjunction with the lookup arrow expression, described in 4.23.3 Lookup Arrow Expressions. For example, given the declaration:

declare record geom:rectangle(
  width  as xs:double,
  height as xs:double,
  area   as fn(geom:rectangle) as xs:double := fn($this as geom:rectangle) { 
    $this?width × $this?height 
  }
);

The following expression constructs a rectangle and calculates its area:

let $box := geom:rectangle(3, 2)
return $box =?> area()

Note:

There is nothing to stop a user constructing an instance of geom:rectangle in which the area field holds some different function; while the syntax imitates that of object-oriented languages, there is no encapsulation.

5.21 Option Declarations

[Definition: An option declaration declares an option that affects the behavior of a particular implementation. Each option consists of an identifying EQName and a StringLiteral.]

OptionDecl::="declare" "option" EQNameStringLiteral

Typically, a particular option will be recognized by some implementations and not by others. The syntax is designed so that option declarations can be successfully parsed by all implementations.

If the EQName of an option is a lexical QName with a prefix, it must resolve to a namespace URI and local name, using the statically known namespaces [err:XPST0081].

If the EQName of an option is a lexical QName that does not have a prefix, the expanded QName is in the http://www.w3.org/2012/xquery namespace, which is reserved for option declarations defined by the XQuery family of specifications. XQuery does not currently define declaration options in this namespace.

Each implementation recognizes the http://www.w3.org/2012/xquery namespace URI and and all options defined in this namespace in this specification. In addition, each implementation recognizes an implementation-defined set of namespace URIs and an implementation-defined set of option names defined in those namespaces. If the namespace part of an option declaration's name is not recognized, the option declaration is ignored.

Otherwise, the effect of the option declaration, including its error behavior, is implementation-defined. For example, if the local part of the QName is not recognized, or if the StringLiteral does not conform to the rules defined by the implementation for the particular option declaration, the implementation may choose whether to raise an error, ignore the option declaration, or take some other action.

Implementations may impose rules on where particular option declarations may appear relative to variable declarations and function declarations, and the interpretation of an option declaration may depend on its position.

An option declaration must not be used to change the syntax accepted by the processor, or to suppress the detection of static errors. However, it may be used without restriction to modify the semantics of the query. The scope of the option declaration is implementation-defined—for example, an option declaration might apply to the whole query, to the current module, or to the immediately following function declaration.

The following examples illustrate several possible uses for option declarations:

  • This option declaration might be used to specify how comments in source documents returned by the fn:doc() function should be handled:

    declare option exq:strip-comments "true";
  • This option declaration might be used to associate a namespace used in function names with a Java class:

    declare namespace smath = "http://example.org/MathLibrary";
    declare option exq:java-class "smath = java.lang.StrictMath";

5.22 Output Declarations

[XSLT and XQuery Serialization 4.0] defines a set of serialization parameters that govern the serialization process. If an XQuery implementation provides a serialization interface, it may support (and may expose to users) any of the serialization parameters listed (with default values) in in this section. If an implementation does not support one of these parameters, it must ignore it without raising an error.

[Definition: An output declaration is an option declaration in the namespace http://www.w3.org/2010/xslt-xquery-serialization; it is used to declare serialization parameters.] Except for parameter-document, each option corresponds to a serialization parameter element defined in Section B Schema for Serialization ParametersSE. The name of each option is the same as the name of the corresponding serialization parameter element, and the values permitted for each option are the same as the values allowed in the serialization parameter element. For QName values, prefixes are expanded to namespace URIs by means of the statically known namespaces, or if unprefixed, the default namespace for elements and types.

There is no output declaration for use-character-maps, it can be set only by means of a parameter document. When the application requests serialization of the output, the processor may use these parameters to control the way in which the serialization takes place. Processors may also allow external mechanisms for specifying serialization parameters, which may or may not override serialization parameters specified in the query prolog.

The following example illustrates the use of declaration options.

declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization";
declare option output:method "xml";
declare option output:encoding "iso-8859-1";
declare option output:indent "yes";
declare option output:parameter-document "file:///home/serialization-parameters.xml";

An output declaration may appear only in a main module; it is a static error [err:XQST0108] if an output declaration appears in a library module. It is a static error [err:XQST0110] if the same serialization parameter is declared more than once. It is a static error [err:XQST0109] if the local name of an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace is not one of the serialization parameter names listed in C.1 Static Context Components or parameter-document, or if the name of an output declaration is use-character-maps. The default value for the method parameter is "xml". An implementation may define additional implementation-defined serialization parameters in its own namespaces.

If the local name of an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace is parameter-document, the value of the output declaration is treated as a URI literal. The value is a location hint, and identifies an XDM instance in an implementation-defined way. If a processor is performing serialization, it is a static error [err:XQST0119] if the implementation is not able to process the value of the output:parameter-document declaration to produce an XDM instance.

If a processor is performing serialization, the XDM instance identified by an output:parameter-document output declaration specifies the values of serialization parameters in the manner defined by Section 3.1 Setting Serialization Parameters by Means of a Parameter DocumentSE. It is a static error [err:XQST0115] if this yields a serialization error. The value of any other output declaration overrides any value that might have been specified for the same serialization parameter using an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace with the local name parameter-document declaration.

A serialization parameter that is not applicable to the chosen output method must be ignored, except that if its value is not a valid value for that parameter, an error may be raised.

A processor that is performing serialization must raise a serialization error if the values of any serialization parameters that it supports (other than any that are ignored under the previous paragraph) are incorrect.

A processor that is not performing serialization may report errors if any serialization parameters are incorrect, or may ignore such parameters.

Specifying serialization parameters in a query does not by itself demand that the output be serialized. It merely defines the desired form of the serialized output for use in situations where the processor has been asked to perform serialization.

Note:

The data model permits an element node to have fewer in-scope namespaces than its parent. Correct serialization of such an element node would require “undeclaration” of namespaces, which is a feature of [XML Names 1.1]. An implementation that does not support [XML Names 1.1] is permitted to serialize such an element without “undeclaration” of namespaces, which effectively causes the element to inherit the in-scope namespaces of its parent.

5.22.1 Serialization Parameters

ComponentDefault initial value
allow-duplicate-namesno
byte-order-markimplementation-defined
cdata-section-elementsempty
doctype-publicnone
doctype-systemnone
encodingimplementation-defined choice between "utf-8" and "utf-16"
escape-solidusyes
escape-uri-attributesyes
html-versionimplementation-defined
include-content-typeyes
indentno
item-separatorimplementation-defined
json-node-output-methodxml
media-typeimplementation-defined
methodxml
normalization-formimplementation-defined
omit-xml-declarationimplementation-defined
standaloneimplementation-defined
suppress-indentationempty
undeclare-prefixesno
use-character-mapsempty
versionimplementation-defined

6 Conformance

Changes in 4.0  

  1. Support for higher-order functions is now a mandatory feature (in 3.1 it was optional).   [Issue 205 PR 326 1 February 2023]

  2. The static typing feature has been dropped.   [Issue 1343 ]

This section defines the conformance criteria for an XQuery 4.0 processor. In this section, the following terms are used to indicate the requirement levels defined in [RFC2119]. [Definition: MUST means that the item is an absolute requirement of the specification.] [Definition: MUST NOT means that the item is an absolute prohibition of the specification.] [Definition: MAY means that an item is truly optional.] [Definition: SHOULD means that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.]

An XQuery processor that claims to conform to this specification MUST include a claim of Minimal Conformance as defined in 6.1 Minimal Conformance. In addition to a claim of Minimal Conformance, it MAY claim conformance to one or more optional features defined in 6.2 Optional Features.

6.1 Minimal Conformance

An implementation that claims Minimal Conformance to this specification MUST provide all of the following items:

  1. An implementation of everything specified in this document except those features specified in 6.2 Optional Features to be optional. If an implementation does not provide a given optional feature, it MUST implement any requirements specified in 6.2 Optional Features for implementations that do not provide that feature.

  2. A definition of every item specified to be implementation-defined, unless that item is part of an optional feature that is not provided by the implementation. A list of implementation-defined items can be found in D Implementation-Defined Items.

    Note:

    Implementations are not required to define items specified to be implementation-dependent.

  3. An implementation of [XQuery and XPath Data Model (XDM) 4.0], as specified in 6.3 Data Model Conformance, and a definition of every item specified to be implementation-defined, unless that item is part of an optional feature that is not provided by the implementation.

  4. An implementation of all functions defined in [XQuery and XPath Functions and Operators 4.0], and a definition of every item specified to be implementation-defined, unless that function or item is part of an optional feature that is not provided by the implementation.

6.2 Optional Features

The features discussed in this section are optional. An implementation MAY claim conformance to one or more of these features.

The description of each feature mentions any errors that occur if a query relies on a feature that is not present.

6.2.1 Schema Aware Feature

[Definition: The Schema Aware Feature permits the query Prolog to contain a schema import, and permits a query to contain a validate expression (see 4.24 Validate Expressions). ]

If an XQuery implementation does not provide the Schema Aware Feature, it MUST raise a static error [err:XQST0009] if it encounters a schema import, and it MUST raise a static error [err:XQST0075] if it encounters a validate expression.

If an implementation provides the Schema Aware Feature, it MUST also provide the 6.2.2 Typed Data Feature.

6.2.2 Typed Data Feature

[Definition: The Typed Data Feature permits an XDM instance to contain element node types other than xs:untyped and attributes node types other than xs:untypedAtomic.]

If an XQuery implementation does not provide the Typed Data Feature, it MUST guarantee that:

  1. The XDM has the type xs:untyped for every element node and xs:untypedAtomic for every attribute node, including nodes created by the query.

  2. Elements constructed by the query always have the type xs:untyped; attributes constructed by the query always have the type xs:untypedAtomic. (This is equivalent to using construction mode = strip.)

6.2.3 Module Feature

[Definition: The Module Feature allows a query Prolog to contain a Module Import and allows library modules to be created.]

An implementation that does not provide the Module Feature MUST raise a static error [err:XQST0016] if it encounters a module declaration or a module import. Since a module declaration is required in a library module, the Module Feature is required in order to create a library module.

Note:

In the absence of the Module Feature, each query consists of a single main module.

6.2.4 Serialization Feature

[Definition: The Serialization Feature provides means for serializing the result of a query as specified in 2.3.5 Serialization.] A conforming XQuery implementation that provides the Serialization Feature MUST conform to 2.3.5 Serialization. An implementation MAY provide other forms of serialization, which do not conform to the Serialization Feature, and are beyond the scope of this specification.

The means by which serialization is invoked is implementation-defined.

If an error is raised during the serialization process as specified in [XSLT and XQuery Serialization 4.0], an implementation MUST report the error to the calling environment.

An implementation that does not provide the Serialization Feature MUST NOT raise errors when reading an output declaration, and MUST implement fn:serialize; it MAY, however, raise an error when fn:serialize is invoked, as specified in Section 14.1.3 fn:serializeFO. An implementation that does not provide the Serialization Feature MAY provide results of a query using a vendor-defined serialization.

Note:

Some implementations return query results without serialization. For instance, an implementation might provide results via an XML API or a binary representation such as a persistent DOM.

6.3 Data Model Conformance

All XQuery implementations process data represented in the data model as specified in [XQuery and XPath Data Model (XDM) 4.0]. The data model specification relies on languages such as XQuery to specify conformance criteria for the data model in their respective environments, and suggests that the following issues should be considered:

  1. Support for normative construction from an infoset. An implementation MAY choose to claim conformance to Section 3.2 Construction from an InfosetDM, which defines a normative way to construct an XDM instance from an XML document that is merely well-formed or is governed by a DTD.

  2. Support for normative construction from a PSVI. An implementation MAY choose to claim conformance to Section 3.3 Construction from a PSVIDM, which defines a normative way to construct an XDM instance from an XML document that is governed by a W3C XML Schema.

  3. Support for versions of XML and XSD. As stated in [XQuery and XPath Data Model (XDM) 4.0], the definitions of primitives such as strings, characters, and names SHOULD be taken from the latest applicable version of the base specifications in which they are defined; it is implementation-defined which definitions are used in cases where these differ.

    Note:

    For suggestions on processing XML 1.1 documents with XSD 1.0, see [XML 1.1 and Schema 1.0].

  4. Ranges of data values. In XQuery, the following limits are implementation-defined:

    1. For the xs:decimal type, the maximum number of decimal digits (totalDigits facet) MUST be at least 18. This limit SHOULD be at least 20 digits in order to accommodate the full range of values of built-in subtypes of xs:integer, such as xs:long and xs:unsignedLong.

    2. For the types xs:date, xs:dateTime, xs:gYear, and xs:gYearMonth: the minimum and maximum value of the year component (must be at least 1 to 9999).

      For the types xs:time and xs:dateTime: the maximum number of fractional second digits (must be at least 3).

    3. For the xs:duration type: the maximum absolute values of the years, months, days, hours, minutes, and seconds components.

    4. For the xs:yearMonthDuration type: the maximum absolute value, expressed as an integer number of months.

    5. For the xs:dayTimeDuration type: the maximum absolute value, expressed as a decimal number of seconds.

    6. For the types xs:string, xs:hexBinary, xs:base64Binary, xs:QName, xs:anyURI, xs:NOTATION, and types derived from them: limitations (if any) imposed by the implementation on lengths of values.

    The limits listed above need not be fixed, but MAY depend on environmental factors such as system resources. For example, the length of a value of type xs:string might be limited by available memory.

    Note:

    For discussion of errors due to implementation-dependent limits, see 2.4.1 Kinds of Errors.

6.4 Syntax Extensions

Any syntactic extensions to XQuery are implementation-defined. The effect of syntactic extensions, including their error behavior, is implementation-defined. Syntactic extensions MAY be used without restriction to modify the semantics of a XQuery expression.

A XQuery 4.0 Grammar

A.1 EBNF

Changes in 4.0  

  1. The EBNF operators ++ and ** have been introduced, for more concise representation of sequences using a character such as "," as a separator. The notation is borrowed from Invisible XML.  [Issue 1366 PR 1498]

The grammar of XQuery 4.0 uses the same simple Extended Backus-Naur Form (EBNF) notation as [XML 1.0] with the following differences.

  • The notation XYZ ** "," indicates a sequence of zero or more occurrences of XYZ, with a single comma between adjacent occurrences.

  • The notation XYZ ++ "," indicates a sequence of one or more occurrences of XYZ, with a single comma between adjacent occurrences.

  • All named symbols have a name that begins with an uppercase letter.

  • It adds a notation for referring to productions in external specifications.

  • Comments or extra-grammatical constraints on grammar productions are between '/*' and '*/' symbols.

    • A 'xgc:' prefix is an extra-grammatical constraint, the details of which are explained in A.1.2 Extra-grammatical Constraints

    • A 'ws:' prefix explains the whitespace rules for the production, the details of which are explained in A.3.5 Whitespace Rules

    • A 'gn:' prefix means a 'Grammar Note', and is meant as a clarification for parsing rules, and is explained in A.1.3 Grammar Notes. These notes are not normative.

The terminal symbols for this grammar include the quoted strings used in the production rules below, and the terminal symbols defined in section A.3.1 Terminal Symbols. The grammar is a little unusual in that parsing and tokenization are somewhat intertwined: for more details see A.3 Lexical structure.

The EBNF notation is described in more detail in A.1.1 Notation.

AbbrevForwardStep::=("@" NodeTest) | SimpleNodeTest
AbbrevReverseStep::=".."
AdditiveExpr::=MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
AllowingEmpty::="allowing" "empty"
AndExpr::=ComparisonExpr ( "and" ComparisonExpr )*
AnnotatedDecl::="declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl | NamedRecordTypeDecl)
Annotation::="%" EQName ("(" (AnnotationValue ++ ",") ")")?
AnnotationValue::=StringLiteral | ("-"? NumericLiteral) | ("true" "(" ")") | ("false" "(" ")")
AnyArrayType::="array" "(" "*" ")"
AnyFunctionType::=("function" | "fn") "(" "*" ")"
AnyItemTest::="item" "(" ")"
AnyKindTest::="node" "(" ")"
AnyMapType::="map" "(" "*" ")"
AnyRecordType::="record" "(" "*" ")"
AposAttrValueContent::=AposAttrContentChar
| CommonContent
Argument::=ExprSingle | ArgumentPlaceholder
ArgumentList::="(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
ArgumentPlaceholder::="?"
ArrayConstructor::=SquareArrayConstructor | CurlyArrayConstructor
ArrayType::=AnyArrayType | TypedArrayType
ArrowDynamicFunction::=VarRef | InlineFunctionExpr | ParenthesizedExpr
ArrowExpr::=UnaryExpr ( (SequenceArrowTarget | MappingArrowTarget | LookupArrowTarget) )*
ArrowStaticFunction::=EQName
ArrowTarget::=(ArrowStaticFunctionArgumentList) | (ArrowDynamicFunctionPositionalArgumentList)
AttributeName::=EQName
AttributeTest::="attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
AxisStep::=(ReverseStep | ForwardStep) Predicate*
BaseURIDecl::="declare" "base-uri" URILiteral
BoundarySpaceDecl::="declare" "boundary-space" ("preserve" | "strip")
BracedActions::=ThenActionElseIfAction* ElseAction?
BracedSwitchCases::="{" SwitchCases "}"
BracedTypeswitchCases::="{" TypeswitchCases "}"
CaseClause::="case" (VarName "as")? SequenceTypeUnion "return" ExprSingle
CastableExpr::=CastExpr ( "castable" "as" CastTarget "?"? )?
CastExpr::=ArrowExpr ( "cast" "as" CastTarget "?"? )?
CastTarget::=TypeName | ChoiceItemType | EnumerationType
CatchClause::="catch" NameTestUnionEnclosedExpr
CDataSection::="<![CDATA[" CDataSectionContents "]]>"
/* ws: explicit */
CDataSectionContents::=(Char* - (Char* ']]>' Char*))
/* ws: explicit */
ChoiceItemType::="(" (ItemType ++ "|") ")"
CommentTest::="comment" "(" ")"
CommonContent::=PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
ComparisonExpr::=OtherwiseExpr ( (ValueComp
| GeneralComp
| NodeComp) OtherwiseExpr )?
CompAttrConstructor::="attribute" CompNodeNameEnclosedExpr
CompCommentConstructor::="comment" EnclosedExpr
CompDocConstructor::="document" EnclosedExpr
CompElemConstructor::="element" CompNodeNameEnclosedContentExpr
CompNamespaceConstructor::="namespace" CompNodeNCNameEnclosedExpr
CompNodeName::=StringLiteral | UnreservedName | ("{" Expr "}")
CompNodeNCName::=StringLiteral | UnreservedNCName | ("{" Expr "}")
CompPIConstructor::="processing-instruction" CompNodeNCNameEnclosedExpr
CompTextConstructor::="text" EnclosedExpr
ComputedConstructor::=CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompNamespaceConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor
ConstructionDecl::="declare" "construction" ("strip" | "preserve")
ContextValueDecl::="declare" "context" (("value" ("as" SequenceType)?) | ("item" ("as" ItemType)?)) ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
ContextValueRef::="."
CopyNamespacesDecl::="declare" "copy-namespaces" PreserveMode "," InheritMode
CountClause::="count" VarName
CurlyArrayConstructor::="array" EnclosedExpr
CurrentVar::=VarName
DecimalFormatDecl::="declare" (("decimal-format" EQName) | ("default" "decimal-format")) (DFPropertyName "=" StringLiteral)*
DefaultCollationDecl::="declare" "default" "collation" URILiteral
DefaultNamespaceDecl::="declare" "fixed"? "default" ("element" | "function") "namespace" URILiteral
DFPropertyName::="decimal-separator" | "grouping-separator" | "infinity" | "minus-sign" | "NaN" | "percent" | "per-mille" | "zero-digit" | "digit" | "pattern-separator" | "exponent-separator"
DirAttributeList::=(S (QNameS? "=" S? DirAttributeValue)?)*
/* ws: explicit */
DirAttributeValue::=('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
DirCommentConstructor::="<!--" DirCommentContents "-->"
/* ws: explicit */
DirCommentContents::=((Char - '-') | ('-' (Char - '-')))*
/* ws: explicit */
DirectConstructor::=DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
DirElemConstructor::="<" QNameDirAttributeList ("/>" | (">" DirElemContent* "</" QNameS? ">"))
/* ws: explicit */
DirElemContent::=DirectConstructor
| CDataSection
| CommonContent
| ElementContentChar
DirPIConstructor::="<?" PITarget (SDirPIContents)? "?>"
/* ws: explicit */
DirPIContents::=(Char* - (Char* '?>' Char*))
/* ws: explicit */
DocumentTest::="document-node" "(" (ElementTest | SchemaElementTest | NameTestUnion)? ")"
DynamicFunctionCall::=PostfixExprPositionalArgumentList
ElementName::=EQName
ElementTest::="element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
ElseAction::="else" EnclosedExpr
ElseIfAction::="else" "if" "(" Expr ")" EnclosedExpr
EmptyOrderDecl::="declare" "default" "order" "empty" ("greatest" | "least")
EnclosedContentExpr::=EnclosedExpr
EnclosedExpr::="{" Expr? "}"
EnumerationType::="enum" "(" (StringLiteral ++ ",") ")"
EQName::=QName | URIQualifiedName
Expr::=(ExprSingle ++ ",")
ExprSingle::=FLWORExpr
| QuantifiedExpr
| SwitchExpr
| TypeswitchExpr
| IfExpr
| TryCatchExpr
| OrExpr
ExtendedFieldDeclaration::=FieldDeclaration (":=" ExprSingle)?
ExtensibleFlag::="," "*"
ExtensionExpr::=Pragma+ "{" Expr? "}"
FieldDeclaration::=FieldName "?"? ("as" SequenceType)?
FieldName::=NCName | StringLiteral
FilterExpr::=PostfixExprPredicate
FilterExprAM::=PostfixExpr "?[" Expr "]"
FLWORExpr::=InitialClauseIntermediateClause* ReturnClause
ForBinding::=ForItemBinding | ForMemberBinding | ForEntryBinding
ForClause::="for" (ForBinding ++ ",")
ForEntryBinding::=((ForEntryKeyBindingForEntryValueBinding?) | ForEntryValueBinding) PositionalVar? "in" ExprSingle
ForEntryKeyBinding::="key" VarNameAndType
ForEntryValueBinding::="value" VarNameAndType
ForItemBinding::=VarNameAndTypeAllowingEmpty? PositionalVar? "in" ExprSingle
ForMemberBinding::="member" VarNameAndTypePositionalVar? "in" ExprSingle
ForwardAxis::=("attribute"
| "child"
| "descendant"
| "descendant-or-self"
| "following"
| "following-or-self"
| "following-sibling"
| "following-sibling-or-self"
| "self") "::"
ForwardStep::=(ForwardAxisNodeTest) | AbbrevForwardStep
FunctionBody::=EnclosedExpr
FunctionCall::=EQNameArgumentList
/* xgc: reserved-function-names */
/* gn: parens */
FunctionDecl::="function" EQName "(" ParamListWithDefaults? ")" TypeDeclaration? (FunctionBody | "external")
/* xgc: reserved-function-names */
FunctionItemExpr::=NamedFunctionRef | InlineFunctionExpr
FunctionSignature::="(" ParamList ")" TypeDeclaration?
FunctionType::=Annotation* (AnyFunctionType
| TypedFunctionType)
GeneralComp::="=" | "!=" | "<" | "<=" | ">" | ">="
GroupByClause::="group" "by" (GroupingSpec ++ ",")
GroupingSpec::=VarName (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
IfExpr::="if" "(" Expr ")" (UnbracedActions | BracedActions)
Import::=SchemaImport | ModuleImport
InheritMode::="inherit" | "no-inherit"
InitialClause::=ForClause | LetClause | WindowClause
InlineFunctionExpr::=Annotation* ("function" | "fn") FunctionSignature? FunctionBody
InstanceofExpr::=TreatExpr ( "instance" "of" SequenceType )?
IntermediateClause::=InitialClause | WhereClause | WhileClause | GroupByClause | OrderByClause | CountClause
IntersectExceptExpr::=InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*
ItemType::=AnyItemTest | TypeName | KindTest | FunctionType | MapType | ArrayType | RecordType | EnumerationType | ChoiceItemType
ItemTypeDecl::="type" EQName "as" ItemType
KeySpecifier::=NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | LookupWildcard
KeywordArgument::=EQName ":=" Argument
KeywordArguments::=(KeywordArgument ++ ",")
KindTest::=DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
LetBinding::=VarNameAndType ":=" ExprSingle
LetClause::="let" (LetBinding ++ ",")
LibraryModule::=ModuleDeclProlog
Literal::=NumericLiteral | StringLiteral
Lookup::=("?" | "??") (Modifier "::")? KeySpecifier
LookupArrowTarget::="=?>" NCNamePositionalArgumentList
LookupExpr::=PostfixExprLookup
LookupWildcard::="*"
MainModule::=PrologQueryBody
MapConstructor::="map"? "{" (MapConstructorEntry ** ",") "}"
MapConstructorEntry::=MapKeyExpr ":" MapValueExpr
MapKeyExpr::=ExprSingle
MappingArrowTarget::="=!>" ArrowTarget
MapType::=AnyMapType | TypedMapType
MapValueExpr::=ExprSingle
Modifier::="pairs" | "keys" | "values" | "items"
Module::=VersionDecl? (LibraryModule | MainModule)
ModuleDecl::="module" "namespace" NCName "=" URILiteralSeparator
ModuleImport::="import" "module" ("namespace" NCName "=")? URILiteral ("at" (URILiteral ++ ","))?
MultiplicativeExpr::=UnionExpr ( ("*" | "×" | "div" | "÷" | "idiv" | "mod") UnionExpr )*
NamedFunctionRef::=EQName "#" IntegerLiteral
/* xgc: reserved-function-names */
NamedRecordTypeDecl::="record" EQName "(" (ExtendedFieldDeclaration ** ",") ExtensibleFlag? ")"
NamespaceDecl::="declare" "namespace" NCName "=" URILiteral
NamespaceNodeTest::="namespace-node" "(" ")"
NameTest::=EQName | Wildcard
NameTestUnion::=(NameTest ++ "|")
NextVar::="next" VarName
NodeComp::="is" | "<<" | ">>"
NodeConstructor::=DirectConstructor
| ComputedConstructor
NodeTest::=UnionNodeTest | SimpleNodeTest
NumericLiteral::=IntegerLiteral | HexIntegerLiteral | BinaryIntegerLiteral | DecimalLiteral | DoubleLiteral
OccurrenceIndicator::="?" | "*" | "+"
/* xgc: occurrence-indicators */
OptionDecl::="declare" "option" EQNameStringLiteral
OrderByClause::="stable"? "order" "by" OrderSpec ("," OrderSpec)*
OrderedExpr::="ordered" EnclosedExpr
OrderingModeDecl::="declare" "ordering" ("ordered" | "unordered")
OrderModifier::=("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?
OrderSpec::=ExprSingleOrderModifier
OrExpr::=AndExpr ( "or" AndExpr )*
OtherwiseExpr::=StringConcatExpr ( "otherwise" StringConcatExpr )*
ParamList::=(VarNameAndType ** ",")
ParamListWithDefaults::=(ParamWithDefault ++ ",")
ParamWithDefault::=VarNameAndType (":=" ExprSingle)?
ParenthesizedExpr::="(" Expr? ")"
PathExpr::=("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* xgc: leading-lone-slash */
PITest::="processing-instruction" "(" (NCName | StringLiteral)? ")"
PositionalArgumentList::="(" PositionalArguments? ")"
PositionalArguments::=(Argument ++ ",")
PositionalVar::="at" VarName
PostfixExpr::=PrimaryExpr | FilterExpr | DynamicFunctionCall | LookupExpr | FilterExprAM
Pragma::="(#" S? EQName (SPragmaContents)? "#)"
/* ws: explicit */
PragmaContents::=(Char* - (Char* '#)' Char*))
Predicate::="[" Expr "]"
PreserveMode::="preserve" | "no-preserve"
PreviousVar::="previous" VarName
PrimaryExpr::=Literal
| VarRef
| ParenthesizedExpr
| ContextValueRef
| FunctionCall
| OrderedExpr
| UnorderedExpr
| NodeConstructor
| FunctionItemExpr
| MapConstructor
| ArrayConstructor
| StringTemplate
| StringConstructor
| UnaryLookup
Prolog::=((DefaultNamespaceDecl | Setter | NamespaceDecl | Import) Separator)* ((ContextValueDecl | AnnotatedDecl | OptionDecl) Separator)*
QuantifiedExpr::=("some" | "every") QuantifierBinding ("," QuantifierBinding)* "satisfies" ExprSingle
QuantifierBinding::=VarNameAndType "in" ExprSingle
QueryBody::=Expr
QuotAttrValueContent::=QuotAttrContentChar
| CommonContent
RangeExpr::=AdditiveExpr ( "to" AdditiveExpr )?
RecordType::=AnyRecordType | TypedRecordType
RelativePathExpr::=StepExpr (("/" | "//") StepExpr)*
ReturnClause::="return" ExprSingle
ReverseAxis::=("ancestor"
| "ancestor-or-self"
| "parent"
| "preceding"
| "preceding-or-self"
| "preceding-sibling-or-self") "::"
ReverseStep::=(ReverseAxisNodeTest) | AbbrevReverseStep
SchemaAttributeTest::="schema-attribute" "(" AttributeName ")"
SchemaElementTest::="schema-element" "(" ElementName ")"
SchemaImport::="import" "schema" SchemaPrefix? URILiteral ("at" (URILiteral ++ ","))?
SchemaPrefix::=("namespace" NCName "=") | ("fixed"? "default" "element" "namespace")
Separator::=";"
SequenceArrowTarget::="=>" ArrowTarget
SequenceType::=("empty-sequence" "(" ")")
| (ItemTypeOccurrenceIndicator?)
SequenceTypeUnion::=SequenceType ("|" SequenceType)*
Setter::=BoundarySpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl | DecimalFormatDecl
SimpleMapExpr::=PathExpr ("!" PathExpr)*
SimpleNodeTest::=KindTest | NameTest
SlidingWindowClause::="sliding" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition
SquareArrayConstructor::="[" (ExprSingle ** ",") "]"
StepExpr::=PostfixExpr | AxisStep
StringConcatExpr::=RangeExpr ( "||" RangeExpr )*
StringConstructor::="``[" StringConstructorContent "]``"
/* ws: explicit */
StringConstructorChars::=(Char* - (Char* ('`{' | ']``') Char*))
/* ws: explicit */
StringConstructorContent::=StringConstructorChars (StringInterpolationStringConstructorChars)*
/* ws: explicit */
StringInterpolation::="`{" Expr? "}`"
/* ws: explicit */
StringTemplate::="`" (StringTemplateFixedPart | StringTemplateVariablePart)* "`"
/* ws: explicit */
StringTemplateFixedPart::=((Char - ('{' | '}' | '`')) | "{{" | "}}" | "``")*
/* ws: explicit */
StringTemplateVariablePart::=EnclosedExpr
/* ws: explicit */
SwitchCaseClause::=("case" SwitchCaseOperand)+ "return" ExprSingle
SwitchCaseOperand::=Expr
SwitchCases::=SwitchCaseClause+ "default" "return" ExprSingle
SwitchComparand::="(" Expr ")"
SwitchExpr::="switch" SwitchComparand? (SwitchCases | BracedSwitchCases)
TextTest::="text" "(" ")"
ThenAction::=EnclosedExpr
TreatExpr::=CastableExpr ( "treat" "as" SequenceType )?
TryCatchExpr::=TryClauseCatchClause+
TryClause::="try" EnclosedExpr
TumblingWindowClause::="tumbling" "window" VarNameAndType "in" ExprSingleWindowStartCondition? WindowEndCondition?
TypedArrayType::="array" "(" SequenceType ")"
TypeDeclaration::="as" SequenceType
TypedFunctionType::=("function" | "fn") "(" (SequenceType ** ",") ")" "as" SequenceType
TypedMapType::="map" "(" ItemType "," SequenceType ")"
TypedRecordType::="record" "(" (FieldDeclaration ** ",") ExtensibleFlag? ")"
TypeName::=EQName
TypeswitchCases::=CaseClause+ "default" VarName? "return" ExprSingle
TypeswitchExpr::="typeswitch" "(" Expr ")" (TypeswitchCases | BracedTypeswitchCases)
UnaryExpr::=("-" | "+")* ValueExpr
UnaryLookup::=("?" | "??") (Modifier "::")? KeySpecifier
UnbracedActions::="then" ExprSingle "else" ExprSingle
UnionExpr::=IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
UnionNodeTest::="(" SimpleNodeTest ("|" SimpleNodeTest)* ")"
UnorderedExpr::="unordered" EnclosedExpr
UnreservedName::=EQName
/* xgc: unreserved-name */
UnreservedNCName::=NCName
/* xgc: unreserved-name */
URILiteral::=StringLiteral
ValidateExpr::="validate" (ValidationMode | ("type" TypeName))? "{" Expr "}"
ValidationMode::="lax" | "strict"
ValueComp::="eq" | "ne" | "lt" | "le" | "gt" | "ge"
ValueExpr::=ValidateExpr | ExtensionExpr | SimpleMapExpr
VarDecl::="variable" VarNameAndType ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
VarDefaultValue::=ExprSingle
VarName::="$" EQName
VarNameAndType::="$" EQNameTypeDeclaration?
VarRef::="$" EQName
VarValue::=ExprSingle
VersionDecl::="xquery" (("encoding" StringLiteral) | ("version" StringLiteral ("encoding" StringLiteral)?)) Separator
WhereClause::="where" ExprSingle
WhileClause::="while" ExprSingle
Wildcard::="*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
WindowClause::="for" (TumblingWindowClause | SlidingWindowClause)
WindowEndCondition::="only"? "end" WindowVars ("when" ExprSingle)?
WindowStartCondition::="start" WindowVars ("when" ExprSingle)?
WindowVars::=CurrentVar? PositionalVar? PreviousVar? NextVar?

A.1.1 Notation

Changes in 4.0  

  1. The EBNF operators ++ and ** have been introduced, for more concise representation of sequences using a character such as "," as a separator. The notation is borrowed from Invisible XML.  [Issue 1366 PR 1498]

[Definition: Each rule in the grammar defines one symbol, using the following format:

symbol ::= expression

]

[Definition: A terminal is a symbol or string or pattern that can appear in the right-hand side of a rule, but never appears on the left-hand side in the main grammar, although it may appear on the left-hand side of a rule in the grammar for terminals.] The following constructs are used to match strings of one or more characters in a terminal:

[a-zA-Z]

matches any Char with a value in the range(s) indicated (inclusive).

[abc]

matches any Char with a value among the characters enumerated.

[^abc]

matches any Char with a value not among the characters given.

"string" or 'string'

matches the sequence of characters that appear inside the double or single quotation marks.

[http://www.w3.org/TR/REC-example/#NT-Example]

matches any string matched by the production defined in the external specification as per the provided reference.

Patterns (including the above constructs) can be combined with grammatical operators to form more complex patterns, matching more complex sets of character strings. In the examples that follow, A and B represent (sub-)patterns.

(A)

A is treated as a unit and may be combined as described in this list.

A?

matches A or nothing; optional A.

A B

matches A followed by B. This implicit operator has higher precedence than the choice operator |; thus A B | C D is interpreted as (A B) | (C D).

A | B

matches A or B but not both.

A - B

matches any string that matches A but does not match B.

A+

matches one or more occurrences of A. Concatenation has higher precedence than choice; thus A+ | B+ is identical to (A+) | (B+).

A*

matches zero or more occurrences of A. Concatenation has higher precedence than choice; thus A* | B* is identical to (A*) | (B*)

(A ++ B)

matches one or more occurrences of A, with one occurrence of B between adjacent occurrences of A. The notation A ++ B is a shorthand for A (B A)*. The construct is always parenthesized to avoid ambiguity, and although in principle B could be any pattern, in practice the notation is used only when it is a simple string literal (typically but not invariably ",").

For example, (Digit ++ ".") matches 1 or 1.2 or 1.2.3.

(A ** B)

matches zero or more occurrences of A, with one occurrence of B between adjacent occurrences of A. The notation A ** B is a shorthand for (A (B A)*)?. The construct is always parenthesized to avoid ambiguity, and although in principle B could be any pattern, in practice the notation is used only when it is a simple string literal (typically but not invariably ",").

For example, "[" (Digit ** "|") "]" matches [] or [1] or [1|2] or [1|2|3].

A.1.2 Extra-grammatical Constraints

This section contains constraints on the EBNF productions, which are required to parse syntactically valid sentences. The notes below are referenced from the right side of the production, with the notation: /* xgc: <id> */.

Constraint: leading-lone-slash

A single slash may appear either as a complete path expression or as the first part of a path expression in which it is followed by a RelativePathExpr. In some cases, the next terminal after the slash is insufficient to allow a parser to distinguish these two possibilities: a * symbol or a keyword like union could be either an operator or a NameTest. For example, the expression /union/* could be parsed either as (/) union (/*) or as /child::union/child::* (the second interpretation is the one chosen).

The situation where / is followed by < is a little more complicated. In XPath, this is unambiguous: the < can only indicate one of the operators <, <=, or <<. In XQuery, however, it can also be the start of a direct constructor: specifically, a direct constructor for an element node, processing instruction node, or comment node. These constructs are identified by the tokenizer, independently of their syntactic context, as described in A.3 Lexical structure.

The rule adopted is as follows: if the terminal immediately following a slash can form the start of a RelativePathExpr, then the slash must be the beginning of a PathExpr, not the entirety of it.

The terminals that can form the start of a RelativePathExpr are: NCName, QName, URIQualifiedName, StringLiteral, NumericLiteral, Wildcard, and StringTemplate; plus @...*$???%([; and in XQuery StringConstructor and DirectConstructor.

A single slash may be used as the left-hand argument of an operator by parenthesizing it: (/) * 5. The expression 5 * /, on the other hand, is syntactically valid without parentheses.

Constraint: unreserved-name

In a computed node constructor of the form element NNN {}, attribute NNN {}, processing-instruction NNN {}, or namespace NNN {}, XQuery 4.0 allows the name NNN to be written as a plain NCName only if it is not a language keyword: more specifically, if it is not one of the literal terminals taking the form of an NCName that are listed in A.3 Lexical structure. If such names (for example div or value) are to be used as element or attribute names in a computed node constructor, they must be written as a string literal in quotation marks.

This rule is new in XQuery 4.0, and represents a backwards incompatibility. To ease transition, implementations may provide an option to allow such names to be accepted with a warning that the construct is deprecated. The reason for the change is that the construct has proved an obstacle to extending the language without introducing ambiguity or extensive lookahead; it also makes syntax errors difficult to diagnose.

Constraint: xml-version

The version of XML and XML Names (e.g. [XML 1.0] and [XML Names], or [XML 1.1] and [XML Names 1.1]) is implementation-defined. It is recommended that the latest applicable version be used (even if it is published later than this specification). The EBNF in this specification links only to the 1.0 versions. Note also that these external productions follow the whitespace rules of their respective specifications, and not the rules of this specification, in particular A.3.5.1 Default Whitespace Handling. Thus prefix : localname is not a syntactically valid lexical QName for purposes of this specification, just as it is not permitted in a XML document. Also, comments are not permissible on either side of the colon. Also extra-grammatical constraints such as well-formedness constraints must be taken into account.

XML 1.0 and XML 1.1 differ in their handling of C0 control characters (specifically #x1 through #x1F, excluding #x9, #xA, and #xD) and C1 control characters (#x7F through #x9F). In XML 1.0, these C0 characters are prohibited, and the C1 characters are permitted. In XML 1.1, both sets of control characters are permitted, but only if written as character references. It is RECOMMENDED that implementations should follow the XML 1.1 rules in this respect; however, for backwards compatibility with XQuery 1.0 , implementations MAY allow C1 control characters to be used directly.

Note:

Direct use of C1 control characters often suggests a character encoding error, such as using encoding CP-1252 and mislabeling it as iso-8859-1.

Constraint: reserved-function-names

Unprefixed function names spelled the same way as language keywords could make the language impossible to parse. For instance, element(foo) could be taken either as a FunctionCall or as an ElementTest. Therefore, an unprefixed function name must not be any of the names in A.4 Reserved Function Names.

A function named if can be called by binding its namespace to a prefix and using the prefixed form: library:if(foo) instead of if(foo).

Constraint: occurrence-indicators

As written, the grammar in A XQuery 4.0 Grammar is ambiguous for some forms using the "+", "?" and "*"OccurrenceIndicators. The ambiguity is resolved as follows: these operators are tightly bound to the SequenceType expression, and have higher precedence than other uses of these symbols. Any occurrence of "+", "?" or "*", that follows a sequence type is assumed to be an occurrence indicator, which binds to the last ItemType in the SequenceType.

Thus, 4 treat as item() + - 5 must be interpreted as (4 treat as item()+) - 5, taking the '+' as an occurrence indicator and the '-' as a subtraction operator. To force the interpretation of "+" as an addition operator (and the corresponding interpretation of the "-" as a unary minus), parentheses may be used: the form (4 treat as item()) + -5 surrounds the SequenceType expression with parentheses and leads to the desired interpretation.

function () as xs:string * is interpreted as function () as (xs:string *), not as (function () as xs:string) *. Parentheses can be used as shown to force the latter interpretation.

This rule has as a consequence that certain forms which would otherwise be syntactically valid and unambiguous are not recognized: in 4 treat as item() + 5, the "+" is taken as an OccurrenceIndicator, and not as an operator, which means this is not a syntactically valid expression.

A.1.3 Grammar Notes

This section contains general notes on the EBNF productions, which may be helpful in understanding how to interpret and implement the EBNF. These notes are not normative. The notes below are referenced from the right side of the production, with the notation: /* gn: <id> */.

Note:

grammar-note: parens

Lookahead is required to distinguish a FunctionCall from an EQName or keyword followed by a Pragma or Comment. For example: address (: this may be empty :) may be mistaken for a call to a function named "address" unless this lookahead is employed. Another example is for (: whom the bell :) $tolls in 3 return $tolls, where the keyword "for" must not be mistaken for a function name.

grammar-note: comments

Comments are allowed everywhere that ignorable whitespace is allowed, and the Comment symbol does not explicitly appear on the right-hand side of the grammar (except in its own production). See A.3.5.1 Default Whitespace Handling. Note that comments are not allowed in direct constructor content, though they are allowed in nested EnclosedExprs.

A comment can contain nested comments, as long as all "(:" and ":)" patterns are balanced, no matter where they occur within the outer comment.

Note:

Lexical analysis may typically handle nested comments by incrementing a counter for each "(:" pattern, and decrementing the counter for each ":)" pattern. The comment does not terminate until the counter is back to zero.

Some illustrative examples:

  • (: commenting out a (: comment :) may be confusing, but often helpful :) is a syntactically valid Comment, since balanced nesting of comments is allowed.

  • "this is just a string :)" is a syntactically valid expression. However, (: "this is just a string :)" :) will cause a syntax error. Likewise, "this is another string (:" is a syntactically valid expression, but (: "this is another string (:" :) will cause a syntax error. It is a limitation of nested comments that literal content can cause unbalanced nesting of comments.

  • for (: set up loop :) $i in $x return $i is syntactically valid, ignoring the comment.

  • 5 instance (: strange place for a comment :) of xs:integer is also syntactically valid.

  • <eg (: an example:)>{$i//title}</eg> is not syntactically valid.

  • <eg> (: an example:) </eg> is syntactically valid, but the characters that look like a comment are in fact literal element content.

A.2 Productions Derived from XML

Some productions are defined by reference to the XML and XML Names specifications (e.g. [XML 1.0] and [XML Names], or [XML 1.1] and [XML Names 1.1]. It is implementation-defined which version of these specifications is used; it is recommended that the latest applicable version be used (even if it is published later than this specification).

It is implementation-defined whether the lexical rules of [XML 1.0] and [XML Names] are followed, or alternatively, the lexical rules of [XML 1.1] and [XML Names 1.1] are followed. Implementations that support the full [XML 1.1] character set SHOULD, for purposes of interoperability, provide a mode that follows only the [XML 1.0] and [XML Names] lexical rules.

A.3 Lexical structure

Changes in 4.0  

  1. The rules for tokenization have been largely rewritten. In some cases the revised specification may affect edge cases that were handled in different ways by different 3.1 processors, which could lead to incompatible behavior.   [Issue 327 PR 519 30 May 2023]

This section describes how an XQuery 4.0 text is tokenized prior to parsing.

All keywords are case sensitive. Keywords are not reserved—that is, any lexical QName may duplicate a keyword except as noted in A.4 Reserved Function Names.

Tokenizing an input string is a process that follows the following rules:

  • [Definition: An ordinary production rule is a production rule in A.1 EBNF that is not annotated ws:explicit.]

  • [Definition: A literal terminal is a token appearing as a string in quotation marks on the right-hand side of an ordinary production rule.]

    Note:

    Strings that appear in other production rules do not qualify. For example, "]]>" is not a literal terminal, because it appears only in the rule CDataSection, which is not an ordinary production rule; similarly BracedURILiteral does not qualify because it appears only in URIQualifiedName, and "0x" does not qualify because it appears only in HexIntegerLiteral.

    The literal terminals in XQuery 4.0 are: !!=#$%()*+,...///::::=;<<<<===!>=>=?>>>=>>????[@[]{|||}×÷-allowingancestorancestor-or-selfandarrayasascendingatattributebase-uriboundary-spacebycasecastcastablecatchchildcollationcommentconstructioncontextcopy-namespacescountdecimal-formatdecimal-separatordeclaredefaultdescendantdescendant-or-selfdescendingdigitdivdocumentdocument-nodeelementelseemptyempty-sequenceencodingendenumeqeveryexceptexponent-separatorexternalfalsefixedfnfollowingfollowing-or-selffollowing-siblingfollowing-sibling-or-selfforfunctiongegreatestgroupgrouping-separatorgtidivifimportininfinityinheritinstanceintersectisitemitemskeykeyslaxleleastletltmapmemberminus-signmodmodulenamespacenamespace-nodeNaNnenextno-inheritno-preservenodeofonlyoptionororderorderedorderingotherwisepairsparentpattern-separatorper-millepercentprecedingpreceding-or-selfpreceding-sibling-or-selfpreservepreviousprocessing-instructionrecordreturnsatisfiesschemaschema-attributeschema-elementselfslidingsomestablestartstrictstripswitchtextthentotreattruetrytumblingtypetypeswitchunionunorderedvalidatevaluevaluesvariableversionwhenwherewhilewindowxqueryzero-digit

  • [Definition: A variable terminal is an instance of a production rule that is not itself an ordinary production rule but that is named (directly) on the right-hand side of an ordinary production rule.]

    The variable terminals in XQuery 4.0 are: BinaryIntegerLiteralCDataSectionDecimalLiteralDirCommentConstructorDirElemConstructorDirPIConstructorDoubleLiteralHexIntegerLiteralIntegerLiteralNCNamePragmaQNameStringConstructorStringLiteralStringTemplateURIQualifiedNameWildcard

  • [Definition: A complex terminal is a variable terminal whose production rule references, directly or indirectly, an ordinary production rule.]

    The complex terminals in XQuery 4.0 are: DirElemConstructorPragmaStringConstructorStringTemplate

    Note:

    The significance of complex terminals is that at one level, a complex terminal is treated as a single token, but internally it may contain arbitrary expressions that must be parsed using the full EBNF grammar.

  • Tokenization is the process of splitting the supplied input string into a sequence of terminals, where each terminal is either a literal terminal or a variable terminal (which may itself be a complex terminal). Tokenization is done by repeating the following steps:

    1. Starting at the current position, skip any whitespace and comments.

    2. If the current position is not the end of the input, then return the longest literal terminal or variable terminal that can be matched starting at the current position, regardless whether this terminal is valid at this point in the grammar. If no such terminal can be identified starting at the current position, or if the terminal that is identified is not a valid continuation of the grammar rules, then a syntax error is reported.

      Note:

      Here are some examples showing the effect of the longest token rule:

      • The expression map{a:b} is a syntax error. Although there is a tokenization of this string that satisfies the grammar (by treating a and b as separate expressions), this tokenization does not satisfy the longest token rule, which requires that a:b is interpreted as a single QName.

      • The expression 10 div3 is a syntax error. The longest token rule requires that this be interpreted as two tokens ("10" and "div3") even though it would be a valid expression if treated as three tokens ("10", "div", and "3").

      • The expression $x-$y is a syntax error. This is interpreted as four tokens, ("$", "x-", "$", and "y").

      Note:

      The lexical production rules for variable terminals have been designed so that there is minimal need for backtracking. For example, if the next terminal starts with "0x", then it can only be either a HexIntegerLiteral or an error; if it starts with "`" (and not with "```") then it can only be a StringTemplate or an error. Direct element constructors in XQuery, however, need special treatment, described below.

      This convention, together with the rules for whitespace separation of tokens (see A.3.2 Terminal Delimitation) means that the longest-token rule does not normally result in any need for backtracking. For example, suppose that a variable terminal has been identified as a StringTemplate by examining its first few characters. If the construct turns out not to be a valid StringTemplate, an error can be reported without first considering whether there is some shorter token that might be returned instead.

  • Tokenization requires special care when the current character is U+003C (LESS-THAN SIGN, <) :

    • If the following character is U+003D (EQUALS SIGN, =) then the token can be identified unambiguously as the operator <=.

    • If the following character is U+003C (LESS-THAN SIGN, <) then the token can be identified unambiguously as the operator <<.

    • If the following character is U+0021 (EXCLAMATION MARK, !) then the token can be identified unambiguously as being a DirCommentConstructor (a CDataSection, which also starts with <! can appear only within a direct element constructor, not as a free-standing token).

    • If the following character is U+003F (QUESTION MARK, ?) , then the token is identified as a DirPIConstructor if and only if a match for the relevant production ("<?" PITarget (S DirPIContents)? "?>") is found. If there is no such match, then the string "<?" is identified as a less-than operator followed by a lookup operator.

    • If the following character is a NameStartChar then the token is identified as a DirElemConstructor if and only if a match for the leading part of a DirElemConstructor is found: specifically if a substring starting at the U+003C (LESS-THAN SIGN, <) character matches one of the following regular expressions:

      ^<\i\c*\s*> (as in <element>...)
      ^<\i\c*\s*/>(as in <element/>)
      ^<\i\c*\s+\i\c*\s*=(as in <element att=...)

      If the content matches one of these regular expressions but further analysis shows that the subsequent content does not satisfy the DirElemConstructor production, then a static error is reported.

      If the content does not match any of these regular expressions then the token is identified as the less-than operator <.

    • If the following character is any other character then the token can be identified unambiguously as the less-than operator <.

    This analysis is done without regard to the syntactic context of the U+003C (LESS-THAN SIGN, <) character. However, a tokenizer may avoid looking for a DirPIConstructor or DirElemConstructor if it knows that such a constructor cannot appear in the current syntactic context.

    Note:

    The rules here are described much more precisely than in XQuery 3.1, and the results in edge cases might be incompatible with some XQuery 3.1 processors.

    Note:

    To avoid potential confusion, simply add whitespace after any less-than operator.

  • Tokenization unambiguously identifies the boundaries of the terminals in the input, and this can be achieved without backtracking or lookahead. However, tokenization does not unambiguously classify each terminal. For example, it might identify the string "div" as a terminal, but it does not resolve whether this is the operator symbol div, or an NCName or QName used as a node test or as a variable or function name. Classification of terminals generally requires information about the grammatical context, and in some cases requires lookahead.

    Note:

    Operationally, classification of terminals may be done either in the tokenizer or the parser, or in some combination of the two. For example, according to the EBNF, the expression "parent::x" is made up of three tokens, "parent", "::", and "x". The name "parent" can be classified as an axis name as soon as the following token "::" is recognized, and this might be done either in the tokenizer or in the parser. (Note that whitespace and comments are allowed both before and after "::".)

  • In the case of a complex terminal, identifying the end of the complex terminal typically involves invoking the parser to process any embedded expressions. Tokenization, as described here, is therefore a recursive process. But other implementations are possible.

Note:

Previous versions of this specification included the statement: When tokenizing, the longest possible match that is consistent with the EBNF is used.

Different processors are known to have interpreted this in different ways. One interpretation, for example, was that the expression 10 div-3 should be split into four tokens (10, div, -, 3) on the grounds that any other tokenization would give a result that was inconsistent with the EBNF grammar. Other processors report a syntax error on this example.

This rule has therefore been rewritten in version 4.0. Tokenization is now entirely insensitive to the grammatical context; div-3 is recognized as a single token even though this results in a syntax error. For some implementations this may mean that expressions that were accepted in earlier releases are no longer accepted in 4.0.

A more subtle example is: (. <?b ) cast as xs:integer?> 0) in which <?b ) cast as xs:integer?> is recognized as a single token (a direct processing instruction constructor) even though such a token cannot validly appear in this grammatical context.

A.3.1 Terminal Symbols

IntegerLiteral::=Digits
/* ws: explicit */
HexIntegerLiteral::="0x" HexDigits
/* ws: explicit */
BinaryIntegerLiteral::="0b" BinaryDigits
/* ws: explicit */
DecimalLiteral::=("." Digits) | (Digits "." Digits?)
/* ws: explicit */
DoubleLiteral::=(("." Digits) | (Digits ("." Digits?)?)) [eE] [+-]? Digits
/* ws: explicit */
StringLiteral::=AposStringLiteral | QuotStringLiteral
/* ws: explicit */
AposStringLiteral::="'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'"
/* ws: explicit */
QuotStringLiteral::='"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"'
/* ws: explicit */
URIQualifiedName::=BracedURILiteralNCName
/* ws: explicit */
BracedURILiteral::="Q" "{" (PredefinedEntityRef | CharRef | [^&{}])* "}"
/* ws: explicit */
PredefinedEntityRef::="&" ("lt" | "gt" | "amp" | "quot" | "apos") ";"
/* ws: explicit */
EscapeQuot::='""'
/* ws: explicit */
EscapeApos::="''"
/* ws: explicit */
ElementContentChar::=(Char - [{}<&])
QuotAttrContentChar::=(Char - ["{}<&])
AposAttrContentChar::=(Char - ['{}<&])
Comment::="(:" (CommentContents | Comment)* ":)"
/* ws: explicit */
/* gn: comments */
PITarget::=[http://www.w3.org/TR/REC-xml#NT-PITarget]XML
/* xgc: xml-version */
CharRef::=[http://www.w3.org/TR/REC-xml#NT-CharRef]XML
/* xgc: xml-version */
QName::=[http://www.w3.org/TR/REC-xml-names/#NT-QName]Names
/* xgc: xml-version */
NCName::=[http://www.w3.org/TR/REC-xml-names/#NT-NCName]Names
/* xgc: xml-version */
S::=[http://www.w3.org/TR/REC-xml#NT-S]XML
/* xgc: xml-version */
Char::=[http://www.w3.org/TR/REC-xml#NT-Char]XML
/* xgc: xml-version */

The following symbols are used only in the definition of terminal symbols; they are not terminal symbols in the grammar of A.1 EBNF.

Digits::=DecDigit ((DecDigit | "_")* DecDigit)?
/* ws: explicit */
DecDigit::=[0-9]
/* ws: explicit */
HexDigits::=HexDigit ((HexDigit | "_")* HexDigit)?
/* ws: explicit */
HexDigit::=[0-9a-fA-F]
/* ws: explicit */
BinaryDigits::=BinaryDigit ((BinaryDigit | "_")* BinaryDigit)?
/* ws: explicit */
BinaryDigit::=[01]
/* ws: explicit */
CommentContents::=(Char+ - (Char* ('(:' | ':)') Char*))
/* ws: explicit */

A.3.2 Terminal Delimitation

XQuery 4.0 expressions consist of terminal symbols and symbol separators.

Literal and variable terminal symbols are of two kinds: delimiting and non-delimiting.

[Definition: The delimiting terminal symbols are: !!=#$%()**:,-...::*:::=;<<<===!>=>=?>>>=>>????[@[]```{{{|||}}}×÷AposStringLiteralBracedURILiteral]]><![CDATA[--><!--/></<+#)(#?><?QuotStringLiteralS///]````[}``{StringLiteral ]

[Definition: The non-delimiting terminal symbols are: allowingancestorancestor-or-selfandarrayasatattributebase-uriboundary-spacebycasecastcastablecatchchildcollationcommentconstructioncontextcopy-namespacescountdecimal-formatdecimal-separatordeclaredefaultdescendantdescendant-or-selfdigitdivdocumentdocument-nodeelementelseemptyempty-sequenceencodingendenumeqeveryexceptexponent-separatorfalsefixedfnfollowingfollowing-or-selffollowing-siblingfollowing-sibling-or-selfforfunctiongegroupgrouping-separatorgtidivifimportininfinityinheritinstanceintersectisitemitemskeykeyslaxleletltmapmemberminus-signmodmodulenamespacenamespace-nodeNaNnenextno-inheritno-preservenodeofonlyoptionororderorderedorderingotherwisepairsparentpattern-separatorper-millepercentprecedingpreceding-or-selfpreceding-sibling-or-selfpreservepreviousprocessing-instructionrecordreturnsatisfiesschemaschema-attributeschema-elementselfslidingsomestablestartstrictstripswitchtextthentotreattruetrytumblingtypetypeswitchunionunorderedvalidatevaluevaluesvariableversionwhenwherewhilewindowxqueryzero-digitascendingBinaryIntegerLiteralDecimalLiteraldescendingDoubleLiteralexternalgreatestHexIntegerLiteralIntegerLiteralleastNCNameQNameURIQualifiedName ]

[Definition: Whitespace and Comments function as symbol separators. For the most part, they are not mentioned in the grammar, and may occur between any two terminal symbols mentioned in the grammar, except where that is forbidden by the /* ws: explicit */ annotation in the EBNF, or by the /* xgc: xml-version */ annotation.]

As a consequence of the longest token rule (see A.3 Lexical structure), one or more symbol separators are required between two consecutive terminal symbols T and U (where T precedes U) when any of the following is true:

A.3.3 Less-Than and Greater-Than Characters

The operator symbols <, <=, >, >=, <<, >>, =>, =!>, and =?> have alternative representations using the characters U+FF1C (FULL-WIDTH LESS-THAN SIGN, ) and U+FF1E (FULL-WIDTH GREATER-THAN SIGN, ) in place of U+003C (LESS-THAN SIGN, <) and U+003E (GREATER-THAN SIGN, >) . The alternative tokens are respectively , <=, , >=, <<, >>, =>, =!>, and =?>. In order to avoid visual confusion these alternatives are not shown explicitly in the grammar.

This option is provided to improve the readability of XPath expressions embedded in XML-based host languages such as XSLT; it enables these operators to be depicted using characters that do not require escaping as XML entities or character references.

This rule does not apply to the < and > symbols used to delimit node constructor expressions, which (because they mimic XML syntax) must use U+003C (LESS-THAN SIGN, <) and U+003E (GREATER-THAN SIGN, >) respectively.

A.3.4 End-of-Line Handling

Prior to parsing, the XQuery 4.0 processor must normalize all line breaks. The rules for line breaking follow the rules of [XML 1.0] or [XML 1.1]. It is implementation-defined which version is used.

A.3.4.1 XML 1.0 End-of-Line Handling

For [XML 1.0] processing, all of the following must be translated to a single U+000A (NEWLINE) :

  1. the two-character sequence U+000D (CARRIAGE RETURN) , U+000A (NEWLINE) ;

  2. any U+000D (CARRIAGE RETURN) character that is not immediately followed by U+000A (NEWLINE) .

A.3.4.2 XML 1.1 End-of-Line Handling

For [XML 1.1] processing, all of the following must be translated to a single U+000A (NEWLINE) character:

  1. the two-character sequence U+000D (CARRIAGE RETURN) , U+000A (NEWLINE) ;

  2. the two-character sequence U+000D (CARRIAGE RETURN) , U+0085 (NEXT LINE, NEL) ;

  3. the single character U+0085 (NEXT LINE, NEL) ;

  4. the single character U+2028 (LINE SEPARATOR) ;

  5. any U+000D (CARRIAGE RETURN) character that is not immediately followed by U+000A (NEWLINE) or U+0085 (NEXT LINE, NEL) .

The characters U+0085 (NEXT LINE, NEL) and U+2028 (LINE SEPARATOR) cannot be reliably recognized and translated until the VersionDecl declaration (if present) has been read.

A.3.5 Whitespace Rules

A.3.5.1 Default Whitespace Handling

[Definition: A whitespace character is any of the characters defined by [http://www.w3.org/TR/REC-xml/#NT-S].]

[Definition: Ignorable whitespace consists of any whitespace characters that may occur between terminals, unless these characters occur in the context of a production marked with a ws:explicit annotation, in which case they can occur only where explicitly specified (see A.3.5.2 Explicit Whitespace Handling).] Ignorable whitespace characters are not significant to the semantics of an expression. Whitespace is allowed before the first terminal and after the last terminal of a module. Whitespace is allowed between any two terminals. Comments may also act as "whitespace" to prevent two adjacent terminals from being recognized as one. Some illustrative examples are as follows:

  • foo- foo results in a syntax error. "foo-" would be recognized as a QName.

  • foo -foo is syntactically equivalent to foo - foo, two QNames separated by a subtraction operator.

  • foo(: This is a comment :)- foo is syntactically equivalent to foo - foo. This is because the comment prevents the two adjacent terminals from being recognized as one.

  • foo-foo is syntactically equivalent to single QName. This is because "-" is a valid character in a QName. When used as an operator after the characters of a name, the "-" must be separated from the name, e.g. by using whitespace or parentheses.

  • 10div 3 results in a syntax error.

  • 10 div3 also results in a syntax error.

  • 10div3 also results in a syntax error.

A.3.5.2 Explicit Whitespace Handling

Explicit whitespace notation is specified with the EBNF productions, when it is different from the default rules, using the notation shown below. This notation is not inherited. In other words, if an EBNF rule is marked as /* ws: explicit */, the notation does not automatically apply to all the 'child' EBNF productions of that rule.

ws: explicit

/* ws: explicit */ means that the EBNF notation explicitly notates, with S or otherwise, where whitespace characters are allowed. In productions with the /* ws: explicit */ annotation, A.3.5.1 Default Whitespace Handling does not apply. Comments are not allowed in these productions except where the Comment non-terminal appears.

For example, whitespace is not freely allowed by the direct constructor productions, but is specified explicitly in the grammar, in order to be more consistent with XML.

A.4 Reserved Function Names

Changes in 4.0  

  1. XQuery 3.0 included empty-sequence and item as reserved function names, and XQuery 3.1 added map and array. This was unnecessary since these names never appear followed by a left parenthesis at the start of an expression. They have therefore been removed from the list. New keywords introducing item types, such as record and enum, have not been included in the list.   [Issue 1208 PR 1212 15 May 2024]

The following names are not allowed as function names in an unprefixed form, because they can appear, followed by a left parenthesis, at the start of an XPath or XQuery expression that is not a function call.

Names used in KindTests:

attribute
comment
document-node
element
namespace-node
node
schema-attribute
schema-element
processing-instruction
text

Names used as syntactic keywords:

fn
function
if
switch
typeswitch

Note:

As the language evolves in the future, it may become necessary to reserve additional names. Furthermore, use of common programming terms like return and while as function names may cause confusion even though they are not reserved. The easiest way to avoid problems is to use an explicit namespace prefix in all calls to user-defined functions.

A.5 Precedence Order (Non-Normative)

The grammar in A.1 EBNF normatively defines built-in precedence among the operators of XQuery. These operators are summarized here to make clear the order of their precedence from lowest to highest. The associativity column indicates the order in which operators of equal precedence in an expression are applied.

#OperatorAssociativity
1, (comma)either
2FLWOR,some, every, switch,typeswitch,try,ifNA
3oreither
4andeither
5eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >>NA
6otherwiseeither
7||left-to-right
8toNA
9+, - (binary)left-to-right
10*, div, idiv, modleft-to-right
11union, |either
12intersect, exceptleft-to-right
13instance ofNA
14treat asNA
15castable asNA
16cast asNA
17=>, =!>, =?>left-to-right
18-, + (unary)right-to-left
19!left-to-right
20/, //left-to-right
21[ ], ?, ??left-to-right
22? (unary)NA

In the "Associativity" column, "either" indicates that all the operators at that level have the associative property (i.e., (A op B) op C is equivalent to A op (B op C)), so their associativity is inconsequential. "NA" (not applicable) indicates that the EBNF does not allow an expression that directly contains multiple operators from that precedence level, so the question of their associativity does not arise.

Note:

Parentheses can be used to override the operator precedence in the usual way. Square brackets in an expression such as A[B] serve two roles: they act as an operator causing B to be evaluated once for each item in the value of A, and they act as parentheses enclosing the expression B.

Curly braces in an expression such as validate { E } or ordered { E } perform a similar bracketing role to the parentheses in a function call, but with the difference in most cases that E is an Expr rather than ExprSingle, meaning that it can use the comma operator.

B Type Promotion and Operator Mapping

B.1 Type Promotion

[Definition: Under certain circumstances, an atomic item can be promoted from one type to another.] Type promotion is used in a number of contexts:

  • It forms part of the process described by the coercion rules, invoked for example when a value of one type is supplied as an argument of a function call where the required type of the corresponding function parameter is declared with a different type.

  • It forms part of the process described in B.2 Operator Mapping, which selects the implementation of a binary operator based on the types of the supplied operands.

  • It is invoked (by explicit reference) in a number of other situations, for example when computing an average of a sequence of numeric values (in the fn:avg function), and in order by clauses (see 4.13.9 Order By Clause).

In general, type promotion takes a set of one or more atomic items as input, potentially having different types, and selects a single common type to which all the input values can be converted by casting.

There are three families of atomic types that can be mixed in this way:

  1. Numeric types. This applies when the input contains values of types xs:decimal, xs:float, and xs:double (including types derived from these, such as xs:integer).

    The rules are:

    1. If any of the items is of type xs:double, then all the values are cast to type xs:double.

    2. Otherwise, if any of the items is of type xs:float, then all the values are cast to type xs:float.

    3. Otherwise, no casting takes place: the values remain as xs:decimal.

  2. String types. This applies when the input contains values of types xs:string and xs:anyURI (including types derived from these, such as xs:NCName).

    The rule is that if any of the items is of type xs:string, then all the values are cast to type xs:string.

  3. Binary types. This applies when the input contains values of types xs:hexBinary and xs:base64Binary (including types derived from these).

    The rule is that if any of the items is of type xs:hexBinary, then all the values are cast to type xs:hexBinary.

B.2 Operator Mapping

Changes in 4.0  

  1. The operator mapping table has been simplified by removing entries for the operators ne, le, gt, and ge; these are now defined by reference to the rules for the operators eq and lt.

The operator mapping tables in this section list the combinations of types for which various operators of XQuery 4.0 are defined. The operators covered by this appendix are the value comparison operators eq and lt, and the arithmetic operators +, -, *, div, idiv, and mod.

Other operators (such as and, or, intersect, union, =, ||, and is) are defined directly in the main body of this document, and do not occur in the operator mapping table.

The operators ne, le, gt, and ge do not occur in the operator mapping table, but are instead defined by the following equivalences:

  • A ne B is equivalent to not(A eq B)

  • A le B is equivalent to A lt B or A eq B

  • A gt B is equivalent to B lt A

  • A ge B is equivalent to B lt A or B eq A

[Definition: For each operator and valid combination of operand types, the operator mapping tables specify a result type and an expression that invokes an operator function; the operator function implements the semantics of the operator for the given types.] The definitions of the operator functions are given in [XQuery and XPath Functions and Operators 4.0]. The result of an operator may be the raising of an error by its operator function, as defined in [XQuery and XPath Functions and Operators 4.0]. The operator function fully defines the semantics of a given operator for the case where the operands are single atomic items of the types given in the table. For the definition of each operator (including its behavior for empty sequences or sequences of length greater than one), see the descriptive material in the main part of this document.

If an operator in the operator mapping tables expects an operand of type ET, that operator can be applied to an operand of type AT if type AT can be converted to type ET by a combination of type promotion and subtype substitution. For example, a table entry indicates that the gt operator may be applied to two xs:date operands, returning xs:boolean. Therefore, the gt operator may also be applied to two (possibly different) subtypes of xs:date, also returning xs:boolean.

[Definition: When referring to a type, the term numeric denotes the types xs:integer, xs:decimal, xs:float, and xs:double which are all member types of the built-in union type xs:numeric.] An operator whose operands and result are designated as numeric might be thought of as representing four operators, one for each of the numeric types. For example, the numeric + operator might be thought of as representing the following four operators:

OperatorFirst operand typeSecond operand typeResult type
+xs:integerxs:integerxs:integer
+xs:decimalxs:decimalxs:decimal
+xs:floatxs:floatxs:float
+xs:doublexs:doublexs:double

A numeric operator may be validly applied to an operand of type AT if type AT can be converted to any of the four numeric types by a combination of type promotion and subtype substitution. If the result type of an operator is listed as numeric, it means "the first type in the ordered list (xs:integer, xs:decimal, xs:float, xs:double) into which all operands can be converted by subtype substitution and type promotion." As an example, suppose that the type hatsize is derived from xs:integer and the type shoesize is derived from xs:float. Then if the + operator is invoked with operands of type hatsize and shoesize, it returns a result of type xs:float. Similarly, if + is invoked with two operands of type hatsize it returns a result of type xs:integer.

[Definition: In the operator mapping tables, the term Gregorian refers to the types xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gDay, and xs:gMonth.] For binary operators that accept two Gregorian-type operands, both operands must have the same type (for example, if one operand is of type xs:gDay, the other operand must be of type xs:gDay.)

[Definition: In the operator mapping tables, the term binary refers to the types xs:hexBinary and xs:base64Binary.] For operators that accept two binary operands, both operands are promoted to type xs:hexBinary.

Binary Operators
OperatorType(A)Type(B)FunctionResult type
A + Bnumericnumericop:numeric-add(A, B)numeric
A + Bxs:datexs:yearMonthDurationop:add-yearMonthDuration-to-date(A, B)xs:date
A + Bxs:yearMonthDurationxs:dateop:add-yearMonthDuration-to-date(B, A)xs:date
A + Bxs:datexs:dayTimeDurationop:add-dayTimeDuration-to-date(A, B)xs:date
A + Bxs:dayTimeDurationxs:dateop:add-dayTimeDuration-to-date(B, A)xs:date
A + Bxs:timexs:dayTimeDurationop:add-dayTimeDuration-to-time(A, B)xs:time
A + Bxs:dayTimeDurationxs:timeop:add-dayTimeDuration-to-time(B, A)xs:time
A + Bxs:dateTimexs:yearMonthDurationop:add-yearMonthDuration-to-dateTime(A, B)xs:dateTime
A + Bxs:yearMonthDurationxs:dateTimeop:add-yearMonthDuration-to-dateTime(B, A)xs:dateTime
A + Bxs:dateTimexs:dayTimeDurationop:add-dayTimeDuration-to-dateTime(A, B)xs:dateTime
A + Bxs:dayTimeDurationxs:dateTimeop:add-dayTimeDuration-to-dateTime(B, A)xs:dateTime
A + Bxs:yearMonthDurationxs:yearMonthDurationop:add-yearMonthDurations(A, B)xs:yearMonthDuration
A + Bxs:dayTimeDurationxs:dayTimeDurationop:add-dayTimeDurations(A, B)xs:dayTimeDuration
A - Bnumericnumericop:numeric-subtract(A, B)numeric
A - Bxs:datexs:dateop:subtract-dates(A, B)xs:dayTimeDuration
A - Bxs:datexs:yearMonthDurationop:subtract-yearMonthDuration-from-date(A, B)xs:date
A - Bxs:datexs:dayTimeDurationop:subtract-dayTimeDuration-from-date(A, B)xs:date
A - Bxs:timexs:timeop:subtract-times(A, B)xs:dayTimeDuration
A - Bxs:timexs:dayTimeDurationop:subtract-dayTimeDuration-from-time(A, B)xs:time
A - Bxs:dateTimexs:dateTimeop:subtract-dateTimes(A, B)xs:dayTimeDuration
A - Bxs:dateTimexs:yearMonthDurationop:subtract-yearMonthDuration-from-dateTime(A, B)xs:dateTime
A - Bxs:dateTimexs:dayTimeDurationop:subtract-dayTimeDuration-from-dateTime(A, B)xs:dateTime
A - Bxs:yearMonthDurationxs:yearMonthDurationop:subtract-yearMonthDurations(A, B)xs:yearMonthDuration
A - Bxs:dayTimeDurationxs:dayTimeDurationop:subtract-dayTimeDurations(A, B)xs:dayTimeDuration
A * Bnumericnumericop:numeric-multiply(A, B)numeric
A * Bxs:yearMonthDurationnumericop:multiply-yearMonthDuration(A, B)xs:yearMonthDuration
A * Bnumericxs:yearMonthDurationop:multiply-yearMonthDuration(B, A)xs:yearMonthDuration
A * Bxs:dayTimeDurationnumericop:multiply-dayTimeDuration(A, B)xs:dayTimeDuration
A * Bnumericxs:dayTimeDurationop:multiply-dayTimeDuration(B, A)xs:dayTimeDuration
A × Bnumericnumericop:numeric-multiply(A, B)numeric
A × Bxs:yearMonthDurationnumericop:multiply-yearMonthDuration(A, B)xs:yearMonthDuration
A × Bnumericxs:yearMonthDurationop:multiply-yearMonthDuration(B, A)xs:yearMonthDuration
A × Bxs:dayTimeDurationnumericop:multiply-dayTimeDuration(A, B)xs:dayTimeDuration
A × Bnumericxs:dayTimeDurationop:multiply-dayTimeDuration(B, A)xs:dayTimeDuration
A idiv Bnumericnumericop:numeric-integer-divide(A, B)xs:integer
A div Bnumericnumericop:numeric-divide(A, B)numeric; but xs:decimal if both operands are xs:integer
A div Bxs:yearMonthDurationnumericop:divide-yearMonthDuration(A, B)xs:yearMonthDuration
A div Bxs:dayTimeDurationnumericop:divide-dayTimeDuration(A, B)xs:dayTimeDuration
A div Bxs:yearMonthDurationxs:yearMonthDurationop:divide-yearMonthDuration-by-yearMonthDuration (A, B)xs:decimal
A div Bxs:dayTimeDurationxs:dayTimeDurationop:divide-dayTimeDuration-by-dayTimeDuration (A, B)xs:decimal
A ÷ Bnumericnumericop:numeric-divide(A, B)numeric; but xs:decimal if both operands are xs:integer
A ÷ Bxs:yearMonthDurationnumericop:divide-yearMonthDuration(A, B)xs:yearMonthDuration
A ÷ Bxs:dayTimeDurationnumericop:divide-dayTimeDuration(A, B)xs:dayTimeDuration
A ÷ Bxs:yearMonthDurationxs:yearMonthDurationop:divide-yearMonthDuration-by-yearMonthDuration (A, B)xs:decimal
A ÷ Bxs:dayTimeDurationxs:dayTimeDurationop:divide-dayTimeDuration-by-dayTimeDuration (A, B)xs:decimal
A mod Bnumericnumericop:numeric-mod(A, B)numeric
A eq Bnumericnumericop:numeric-equal(A, B)xs:boolean
A eq Bxs:booleanxs:booleanop:boolean-equal(A, B)xs:boolean
A eq Bxs:stringxs:stringop:numeric-equal(fn:compare(A, B), 0)xs:boolean
A eq Bxs:datexs:dateop:date-equal(A, B)xs:boolean
A eq Bxs:timexs:timeop:time-equal(A, B)xs:boolean
A eq Bxs:dateTimexs:dateTimeop:dateTime-equal(A, B)xs:boolean
A eq Bxs:durationxs:durationop:duration-equal(A, B)xs:boolean
A eq BGregorianGregorianop:gYear-equal(A, B) etc.xs:boolean
A eq Bbinarybinaryop:binary-equal(A, B)xs:boolean
A eq Bxs:QNamexs:QNameop:QName-equal(A, B)xs:boolean
A eq Bxs:NOTATIONxs:NOTATIONop:NOTATION-equal(A, B)xs:boolean
A lt Bnumericnumericop:numeric-less-than(A, B)xs:boolean
A lt Bxs:booleanxs:booleanop:boolean-less-than(A, B)xs:boolean
A lt Bxs:stringxs:stringop:numeric-less-than(fn:compare(A, B), 0)xs:boolean
A lt Bxs:datexs:dateop:date-less-than(A, B)xs:boolean
A lt Bxs:timexs:timeop:time-less-than(A, B)xs:boolean
A lt Bxs:dateTimexs:dateTimeop:dateTime-less-than(A, B)xs:boolean
A lt Bxs:yearMonthDurationxs:yearMonthDurationop:yearMonthDuration-less-than(A, B)xs:boolean
A lt Bxs:dayTimeDurationxs:dayTimeDurationop:dayTimeDuration-less-than(A, B)xs:boolean
A lt Bbinarybinaryop:binary-less-than(A, B)xs:boolean
Unary Operators
OperatorOperand typeFunctionResult type
+ Anumericop:numeric-unary-plus(A)numeric
- Anumericop:numeric-unary-minus(A)numeric

C Context Components

The tables in this section describe how values are assigned to the various components of the static context and dynamic context.

C.1 Static Context Components

Changes in 4.0 

  1. Parts of the static context that were there purely to assist in static typing, such as the statically known documents, were no longer referenced and have therefore been dropped.   [Issue 1343 ]

The following table describes the components of the static context. The following aspects of each component are described:

  • Default initial value: This is the initial value of the component if it is not overridden or augmented by the implementation or by a query.

  • Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default initial value of the component by a different, implementation-defined value and/or to augment the default initial value by additional implementation-defined values.

  • Can be overwritten or augmented by prolog: Indicates whether there are prolog declarations that can replace and/or augment the initial value provided by default or by the implementation.

  • Can be overwritten or augmented by expressions: Indicates whether there are expressions that can replace and/or augment the value of the component for their subexpressions.

  • Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.3.6 Consistency Constraints.

Static Context Components
ComponentDefault initial valueCan be overwritten or augmented by implementation?Can be overwritten or augmented by prolog?Can be overwritten or augmented by expressions?Consistency rules
Statically known namespacesfn, xml, xs, xsi, localoverwriteable and augmentable (except for xml)overwriteable and augmentable by 5.13 Namespace Declarationoverwriteable and augmentable by element constructorOnly one namespace can be assigned to a given prefix per lexical scope.
Default element/type namespaceno namespaceoverwriteableoverwriteable by 5.14 Default Namespace Declarationoverwriteable by element constructorOnly one default namespace per lexical scope.
In-scope variablesnoneaugmentableoverwriteable and augmentable by 5.16 Variable Declaration and 4.5.2.5 Inline Function Expressions, augmentable by 5.12 Module Importoverwriteable and augmentable by variable-binding expressionsOnly one definition per variable per lexical scope.
Context value static typeitem()overwriteableoverwriteable by 5.17 Context Value Declarationoverwriteable by expressions that set the context valueNone.
Ordering modeorderedoverwriteableoverwriteable by 5.7 Ordering Mode Declarationoverwriteable by expressionValue must be ordered or unordered.
Default function namespacefnoverwriteable (not recommended)overwriteable by 5.14 Default Namespace DeclarationnoNone.
In-scope schema typesbuilt-in types in xsaugmentableaugmentable by 5.11 Schema ImportnoOnly one definition per global or local type.
In-scope element declarationsnoneaugmentableaugmentable by 5.11 Schema ImportnoOnly one definition per global or local element name.
In-scope attribute declarationsnoneaugmentableaugmentable by 5.11 Schema ImportnoOnly one definition per global or local attribute name.
Statically known function signaturesthe signatures of the system functionsaugmentableaugmentable by 5.12 Module Import and by 5.18 Function Declarations; augmentable by 5.11 Schema Import (which adds constructor functions for user-defined types)noEach function must have a unique expanded QName and number of arguments.
Default collationUnicode codepoint collationoverwriteableoverwriteable by 5.4 Default Collation DeclarationnoNone.
Construction modepreserveoverwriteableoverwriteable by 5.6 Construction DeclarationnoValue must be preserve or strip.
Default order for empty sequencesimplementation-definedoverwriteableoverwriteable by 5.8 Empty Order DeclarationnoValue must be greatest or least.
Boundary-space policystripoverwriteableoverwriteable by 5.3 Boundary-space DeclarationnoValue must be preserve or strip.
Copy-namespaces modeinherit, preserveoverwriteableoverwriteable by 5.9 Copy-Namespaces DeclarationnoValue consists of inherit or no-inherit, and preserve or no-preserve.
Static Base URISee rules in 5.5 Base URI Declarationoverwriteableoverwriteable by 5.5 Base URI DeclarationnoValue must be a valid lexical representation of the type xs:anyURI.
Statically known decimal formatsthe default (unnamed) decimal format, which has an implementation-dependent valueaugmentableaugmentable, using decimal format declarationsnoeach QName uniquely identifies a decimal format
Statically known collationsonly the default collationaugmentablenonoEach URI uniquely identifies a collation.
XPath 1.0 Compatibility ModefalsenononoMust be false.

C.2 Dynamic Context Components

The following table describes the components of the dynamic context. The following aspects of each component are described:

  • Default initial value: This is the initial value of the component if it is not overridden or augmented by the implementation or by a query.

  • Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default initial value of the component by a different implementation-defined value and/or to augment the default initial value by additional implementation-defined values.

  • Can be overwritten or augmented by prolog: Indicates whether there are prolog declarations that can replace and/or augment the initial value provided by default or by the implementation.

  • Can be overwritten or augmented by expressions: Indicates whether there are expressions that can replace and/or augment the value of the component for their subexpressions.

  • Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.3.6 Consistency Constraints.

Dynamic Context Components
ComponentDefault initial valueCan be overwritten or augmented by implementation?Can be overwritten or augmented by prolog?Can be overwritten or augmented by expressions?Consistency rules
Context valuenoneoverwriteableoverwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicatesMust be the same in the dynamic context of every module in a query.
Context positionnoneoverwriteableoverwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicatesIf context value is defined, context position must be >0 and <= context size; else context position is absentDM31.
Context sizenone overwriteableoverwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicatesIf context value is defined, context size must be >0; else context size is absentDM31.
Variable valuesnoneaugmentableoverwriteable and augmentable by 5.16 Variable Declaration and 4.5.2.5 Inline Function Expressions, augmentable by 5.12 Module Importoverwriteable and augmentable by variable-binding expressionsNames and values must be consistent with in-scope variables.
Named functionsthe system functionsaugmentableaugmentable by 5.18 Function Declarations, 5.12 Module Import, and 5.11 Schema Import ( (which adds constructor functions for user-defined types)noMust be consistent with statically known function signatures
Current dateTimenonemust be initialized by implementationnonoMust include a timezone. Remains constant during evaluation of a query.
Implicit timezonenonemust be initialized by implementationnonoRemains constant during evaluation of a query.
Available documentsnonemust be initialized by implementationnonoNone
Available text resourcesnonemust be initialized by implementationnonoNone
Available collectionsnonemust be initialized by implementationnonoNone
Default collectionnoneoverwriteablenonoNone
Available URI collectionsnonemust be initialized by implementationnonoNone
Default URI collectionnoneoverwriteablenonoNone

D Implementation-Defined Items

The following items in this specification are implementation-defined:

  1. The version of Unicode that is used to construct expressions.

  2. The statically-known collations.

  3. The implicit timezone.

  4. The circumstances in which warnings are raised, and the ways in which warnings are handled.

  5. The method by which errors are reported to the external processing environment.

  6. Which version of XML and XML Names (e.g. [XML 1.0] and [XML Names] or [XML 1.1] and [XML Names 1.1]) and which version of XML Schema (e.g. [XML Schema 1.0] or [XML Schema 1.1]) is used for the definitions of primitives such as characters and names, and for the definitions of operations such as normalization of line endings and normalization of whitespace in attribute values. It is recommended that the latest applicable version be used (even if it is published later than this specification).

  7. How XDM instances are created from sources other than an Infoset or PSVI.

  8. Any components of the static context or dynamic context that are overwritten or augmented by the implementation.

  9. The default handling of empty sequences returned by an ordering key (orderspec) in an order by clause (empty least or empty greatest).

  10. The names and semantics of any extension expressions (pragmas) recognized by the implementation.

  11. The names and semantics of any option declarations recognized by the implementation.

  12. Protocols (if any) by which parameters can be passed to an external function, and the result of the function can returned to the invoking query.

  13. The process by which the specific modules to be imported by a module import are identified, if the Module Feature is supported (includes processing of location hints, if any.)

  14. The means by which serialization is invoked, if the Serialization Feature is supported.

  15. The default values for the byte-order-mark, encoding, html-version, item-separator, media-type, normalization-form, omit-xml-declaration, standalone, and version parameters, if the Serialization Feature is supported.

  16. The result of an unsuccessful call to an external function (for example, if the function implementation cannot be found or does not return a value of the declared type).

  17. Limits on ranges of values for various data types, as enumerated in 6.3 Data Model Conformance.

  18. Syntactic extensions to XQuery, including both their syntax and semantics, as discussed in 6.4 Syntax Extensions.

  19. Whether the type system is based on [XML Schema 1.0] or [XML Schema 1.1]. An implementation that has based its type system on XML Schema 1.0 is not required to support the use of the xs:dateTimeStamp constructor or the use of xs:dateTimeStamp or xs:error as TypeName in any expression.

  20. The signatures of functions provided by the implementation or via an implementation-defined API (see 2.2.1 Static Context).

  21. Any environment variables provided by the implementation.

  22. Any rules used for static typing (see 2.3.3.1 Static Analysis Phase).

  23. Any serialization parameters provided by the implementation (see 2.3.5 Serialization).

  24. The means by which the location hint for a serialization parameter document identifies the corresponding XDM instance (see 2.3.5 Serialization).

  25. What error, if any, is returned if an external function's implementation does not return the declared result type (see 2.3.6 Consistency Constraints).

  26. Any annotations defined by the implementation, and their associated behavior (see 5.15 Annotations).

  27. Any function assertions defined by the implementation.

  28. The effect of function assertions understood by the implementation on 3.3.3 The judgement subtype-assertions(AnnotationsA, AnnotationsB) .

  29. Any implementation-defined variables defined by the implementation. (see 4.2.2 Variable References).

  30. The ordering associated with fn:unordered in the implementation (see 4.15 Ordered and Unordered Expressions).

  31. Any additional information provided for try/catch via the err:additional variable (see 4.20 Try/Catch Expressions).

  32. The default boundary-space policy (see 5.3 Boundary-space Declaration).

  33. The default collation (see 5.4 Default Collation Declaration).

  34. The default base URI (see 5.5 Base URI Declaration).

E References

E.1 Normative References

RFC2119
S. Bradner. Key Words for use in RFCs to Indicate Requirement Levels. IETF RFC 2119. See http://www.ietf.org/rfc/rfc2119.txt.
RFC3986
T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. IETF RFC 3986. See http://www.ietf.org/rfc/rfc3986.txt.
RFC3987
M. Duerst and M. Suignard. Internationalized Resource Identifiers (IRIs). IETF RFC 3987. See http://www.ietf.org/rfc/rfc3987.txt.
ISO/IEC 10646
ISO (International Organization for Standardization). ISO/IEC 10646:2003. Information technology—Universal Multiple-Octet Coded Character Set (UCS), as, from time to time, amended, replaced by a new edition, or expanded by the addition of new parts. [Geneva]: International Organization for Standardization. (See http://www.iso.org for the latest version.)
Unicode
The Unicode Consortium. The Unicode Standard. Reading, Mass.: Addison-Wesley, 2003, as updated from time to time by the publication of new versions. See http://www.unicode.org/standard/versions/ for the latest version and additional information on versions of the standard and of the Unicode Character Database. The version of Unicode to be used is implementation-defined, but implementations are recommended to use the latest Unicode version.
XML 1.0
World Wide Web Consortium. Extensible Markup Language (XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/REC-xml/. The edition of XML 1.0 must be no earlier than the Third Edition; the edition used is implementation-defined, but we recommend that implementations use the latest version.
XML 1.1
World Wide Web Consortium. Extensible Markup Language (XML) 1.1. W3C Recommendation. See http://www.w3.org/TR/xml11/
XML Base
World Wide Web Consortium. XML Base. W3C Recommendation. See http://www.w3.org/TR/xmlbase/
XML Names
World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/REC-xml-names/
XML Names 1.1
World Wide Web Consortium. Namespaces in XML 1.1. W3C Recommendation. See http://www.w3.org/TR/xml-names11/
XML ID
World Wide Web Consortium. xml:id Version 1.0. W3C Recommendation. See http://www.w3.org/TR/xml-id/
XML Schema 1.0
World Wide Web Consortium. XML Schema, Parts 0, 1, and 2 (Second Edition). W3C Recommendation, 28 October 2004. See http://www.w3.org/TR/xmlschema-0/, http://www.w3.org/TR/xmlschema-1/, and http://www.w3.org/TR/xmlschema-2/.
XML Schema 1.1
World Wide Web Consortium. XML Schema, Parts 1, and 2. W3C Recommendation 5 April 2012. See http://www.w3.org/TR/xmlschema11-1/, and http://www.w3.org/TR/xmlschema11-2/.
XQuery and XPath Data Model (XDM) 4.0
XQuery and XPath Data Model (XDM) 4.0, XSLT Extensions Community Group, World Wide Web Consortium.
XQuery and XPath Functions and Operators 4.0
XQuery and XPath Functions and Operators 4.0, XSLT Extensions Community Group, World Wide Web Consortium.
XPath 4.0
XML Path Language (XPath) 4.0, XSLT Extensions Community Group, World Wide Web Consortium.
XSLT and XQuery Serialization 4.0
XSLT and XQuery Serialization 4.0, XSLT Extensions Community Group, World Wide Web Consortium.

E.2 Non-normative References

XQuery 3.0 Requirements
XQuery 3.0 Requirements, Daniel Engovatov, Jonathan Robie, Editors. World Wide Web Consortium, 08 April 2014. This version is https://www.w3.org/TR/2014/NOTE-xquery-30-requirements-20140408/. The latest version is available at https://www.w3.org/TR/xquery-30-requirements/.
XQuery 3.1 Requirements
XQuery 3.1 Requirements and Use Cases, Jonathan Robie, Editor. World Wide Web Consortium, 13 December 2016. This version is https://www.w3.org/TR/2016/NOTE-xquery-31-requirements-20161213/. The latest version is available at https://www.w3.org/TR/xquery-31-requirements/.
XQuery 3.0: An XML Query Language
XQuery 3.0: An XML Query Language, Jonathan Robie, Don Chamberlin, Michael Dyck, John Snelson, Editors. World Wide Web Consortium, 08 April 2014. This version is https://www.w3.org/TR/2014/REC-xquery-30-20140408/. The latest version is available at https://www.w3.org/TR/xquery-30/.
XQuery 1.0 and XPath 2.0 Formal Semantics
XQuery 1.0 and XPath 2.0 Formal Semantics (Second Edition), Jérôme Siméon, Denise Draper, Peter Frankhauser, et. al., Editors. World Wide Web Consortium, 14 December 2010. This version is https://www.w3.org/TR/2010/REC-xquery-semantics-20101214/. The latest version is available at https://www.w3.org/TR/xquery-semantics/.
XSL Transformations (XSLT) Version 4.0
XSL Transformations (XSLT) Version 4.0, XSLT Extensions Community Group, World Wide Web Consortium.
Document Object Model
World Wide Web Consortium. Document Object Model (DOM) Level 3 Core Specification. W3C Recommendation, April 7, 2004. See http://www.w3.org/TR/DOM-Level-3-Core/.
XML Infoset
World Wide Web Consortium. XML Information Set (Second Edition). W3C Recommendation 4 February 2004. See http://www.w3.org/TR/xml-infoset/
XML Path Language (XPath) Version 1.0
XML Path Language (XPath) Version 1.0, James Clark and Steven DeRose, Editors. World Wide Web Consortium, 16 Nov 1999. This version is http://www.w3.org/TR/1999/REC-xpath-19991116. The latest version is available at http://www.w3.org/TR/xpath.
XML Path Language (XPath) Version 2.0
XML Path Language (XPath) 2.0 (Second Edition), Don Chamberlin, Anders Berglund, Scott Boag, et. al., Editors. World Wide Web Consortium, 14 December 2010. This version is https://www.w3.org/TR/2010/REC-xpath20-20101214/. The latest version is available at https://www.w3.org/TR/xpath20/.
XML Path Language (XPath) Version 3.0
XML Path Language (XPath) 3.0, Jonathan Robie, Don Chamberlin, Michael Dyck, John Snelson, Editors. World Wide Web Consortium, 08 April 2014. This version is https://www.w3.org/TR/2014/REC-xpath-30-20140408/. The latest version is available at https://www.w3.org/TR/xpath-30/.
XML Path Language (XPath) Version 3.1
XML Path Language (XPath) 3.1, Jonathan Robie, Michael Dyck and Josh Spiegel, Editors. World Wide Web Consortium, 21 March 2017. This version is https://www.w3.org/TR/2017/REC-xpath-31-20170321/. The latest version is available at https://www.w3.org/TR/xpath-31/.
XPointer
World Wide Web Consortium. XML Pointer Language (XPointer). W3C Last Call Working Draft 8 January 2001. See http://www.w3.org/TR/WD-xptr
XML Query Use Cases
World Wide Web Consortium. XML Query Use Cases. W3C Working Draft, 8 June 2006. See http://www.w3.org/TR/xquery-use-cases/.
XML 1.1 and Schema 1.0
World Wide Web Consortium. Processing XML 1.1 Documents with XML Schema 1.0 Processors. W3C Working Group Note, 11 May 2005. See http://www.w3.org/TR/xml11schema10/.
Uniform Resource Locators (URL)
Internet Engineering Task Force (IETF). Uniform Resource Locators (URL). Request For Comment No. 1738, Dec. 1994. See http://www.ietf.org/rfc/rfc1738.txt.
ODMG
Rick Cattell et al. The Object Database Standard: ODMG-93, Release 1.2. Morgan Kaufmann Publishers, San Francisco, 1996.
Quilt
Don Chamberlin, Jonathan Robie, and Daniela Florescu. Quilt: an XML Query Language for Heterogeneous Data Sources. In Lecture Notes in Computer Science, Springer-Verlag, Dec. 2000.
XML-QL
Alin Deutsch, Mary Fernandez, Daniela Florescu, Alon Levy, and Dan Suciu. A Query Language for XML.
SQL
International Organization for Standardization (ISO). Information Technology — Database Language SQL. Standard No. ISO/IEC 9075:2011. (Available from American National Standards Institute, New York, NY 10036, (212) 642-4900.)
XQL
J. Robie, J. Lapp, D. Schach. XML Query Language (XQL). See http://www.w3.org/TandS/QL/QL98/pp/xql.html.

E.3 Background Material

Character Model
World Wide Web Consortium. Character Model for the World Wide Web. W3C Working Draft. See http://www.w3.org/TR/charmod/.
XSL Transformations (XSLT) Version 1.0
XSL Transformations (XSLT) Version 1.0, James Clark, Editor. World Wide Web Consortium, 16 Nov 1999. This version is http://www.w3.org/TR/1999/REC-xslt-19991116. The latest version is available at http://www.w3.org/TR/xslt.
Use Case Sample Queries
Queries from the XQuery 1.0 Use Cases, presented in a single file. See http://www.w3.org/2010/12/xquery-30-use-cases/xquery-30-use-case-queries.txt.
XQuery Sample Queries
Queries from this document, presented in a single file. See http://www.w3.org/2013/01/xquery-30-use-cases/xquery-30-example-queries.txt.
Moustache
mustache - Logic-less templates. See http://mustache.github.io/mustache.5.html.

F Error Conditions

err:XPST0001

It is a static error if analysis of an expression relies on some component of the static context that is absentDM.

err:XPDY0002

It is a type error if evaluation of an expression relies on some part of the dynamic context that is absentDM.

Note:

In version 4.0 this has been reclassified as a type error rather than a dynamic error. This change allows a processor to report the error during static analysis where possible; for example if the body of a user-defined function is written as fn($x) { @code }. The error code is prefixed XPDY rather than XPTY for backwards compatibility reasons.

err:XPST0003

It is a static error if an expression is not a valid instance of the grammar defined in A.1 EBNF.

err:XPTY0004

It is a type error if, during the static analysis phase, an expression is found to have a static type that is not appropriate for the context in which the expression occurs, or during the dynamic evaluation phase, the dynamic type of a value does not match a required type as specified by the matching rules in 3.1.2 Sequence Type Matching.

err:XPTY0006

During the analysis phase, an expression is classified as implausible if the inferred static typeS and the required type R are substantively disjoint; more specifically, if neither of the types is a subtype of the other, and if the only values that are instances of both types are one or more of: the empty sequence, the empty map, and the empty array.

err:XPST0008

It is a static error if an expression refers to an element name, attribute name, schema type name, namespace prefix, or variable name that is not defined in the static context, except for an ElementName in an ElementTest or an AttributeName in an AttributeTest.

err:XQST0009

An implementation that does not support the Schema Aware Feature must raise a static error if a Prolog contains a schema import.

err:XQST0012

It is a static error if the set of definitions contained in all schemas imported by a Prolog do not satisfy the conditions for schema validity specified in Sections 3 and 5 of Part 1 of [XML Schema 1.0] or [XML Schema 1.1].

err:XQST0013

It is a static error if an implementation recognizes a pragma but determines that its content is invalid.

err:XQST0016

An implementation that does not support the Module Feature raises a static error if it encounters a module declaration or a module import.

err:XPST0017

It is a static error if the expanded QName and number of arguments in a static function call do not match the name and arity range of a function definition in the static context, or if an argument keyword in the function call does not match a parameter name in that function definition, or if two arguments in the function call bind to the same parameter in the function definition.

err:XPTY0018

It is a type error if the result of a path operator contains both nodes and non-nodes.

err:XPTY0019

It is a type error if E1 in a path expression E1/E2 does not evaluate to a sequence of nodes.

err:XPTY0020

It is a type error if, in an axis step, the context item is not a node.

err:XPST0021

It is a static error if two fields in a record declaration have the same name.

err:XQST0022

It is a static error if a namespace declaration attributecontains an EnclosedExpr.

err:XPST0023

It is a static error if a recursive record type cannot be instantiated (typically because it contains a self-reference that is neither optional nor emptiable). Processors are not required to detect this error.

err:XQTY0024

It is a type error if the content sequence in an element constructor contains an attribute node following a node that is not an attribute node.

err:XQDY0025

It is a dynamic error if any attribute of a constructed element does not have a name that is distinct from the names of all other attributes of the constructed element.

err:XQDY0026

It is a dynamic error if the result of the content expression of a computed processing instruction constructor contains the string "?>".

err:XQDY0027

In a validate expression, it is a dynamic error if the root element information item in the PSVI resulting from validation does not have the expected validity property: valid if validation mode is strict, or either valid or notKnown if validation mode is lax.

err:XQTY0030

It is a type error if the argument of a validate expression does not evaluate to exactly one document or element node.

err:XQST0031

It is a static error if the version number specified in a version declaration is not supported by the implementation.

err:XQST0032

A static error is raised if a Prolog contains more than one base URI declaration.

err:XQST0033

It is a static error if a module contains multiple bindings for the same namespace prefix.

err:XQST0034

It is a static error if multiple functions declared or imported by a module have the same expanded QName and overlapping arity ranges (the arity range of a function declaration is M to M+N, where M is the number of required parameters and N is the number of optional parameters).

err:XQST0035

It is a static error to import two schema components that both define the same name in the same symbol space and in the same scope.

err:XQST0038

It is a static error if a Prolog contains more than one default collation declaration, or the value specified by a default collation declaration is not present in statically known collations.

err:XQST0039

It is a static error for a function declaration oran inline function expression to have more than one parameter with the same name.

err:XQST0040

It is a static error if the attributes specified by a direct element constructor do not have distinct expanded QNames.

err:XQDY0041

It is a dynamic error if the value of the name expression in a computed processing instruction constructor cannot be cast to the type xs:NCName.

err:XQDY0044

It is a dynamic error the node-name of a node constructed by a computed attribute constructor has any of the following properties:

  • Its namespace prefix is xmlns.

  • It has no namespace prefix and its local name is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

err:XQST0045

It is a static error if the name of a variable annotation, a function annotation, or the function name in a function declaration is in a reserved namespace.

err:XQST0046

An implementation MAY raise a static error if the value of a URILiteral or a BracedURILiteral is of nonzero length and is neither an absolute URI nor a relative URI.

err:XQST0047

It is a static error if multiple module imports in the same Prolog specify the same target namespace.

err:XQST0048

It is a static error if a function, variable, or item type declared in a library module is not in the target namespace of the library module.

err:XQST0049

It is a static error if two or more variables declared or imported by a module have equal expanded QNames (as defined by the eq operator.)

err:XPDY0050

It is a dynamic error if the dynamic type of the operand of a treat expression does not match the sequence type designated by the treat expression. This error might also be raised by a path expression beginning with / or // if the context node is not in a tree that is rooted at a document node. This is because a leading / or // in a path expression is an abbreviation for an initial step that includes the clause treat as document-node().

err:XPST0051

It is a static error if an expanded QName used as an ItemType in a SequenceType is not defined in the static context either as a named item type in the in-scope named item types, or as a generalized atomic type in the in-scope schema type.

err:XQST0052

The type named in a cast or castable expression must be the name of a type defined in the in-scope schema types, and the type must be simple.

err:XQDY0054

It is a dynamic error if a cycle is encountered in the definition of a module’s dynamic context components, for example because of a cycle in variable declarations.

err:XQST0055

It is a static error if a Prolog contains more than one copy-namespaces declaration.

err:XQST0057

It is a static error if a schema import binds a namespace prefix but does not specify a target namespace other than a zero-length string.

err:XQST0058

It is a static error if multiple schema imports specify the same target namespace.

err:XQST0059

It is a static error if an implementation is unable to process a schema or module import by finding a schema or module with the specified target namespace.

err:XQST0060

It is a static error if the name of a function in a function declaration is not in a namespace (expanded QName has a null namespace URI).

err:XQDY0061

It is a dynamic error if the operand of a validate expression is a document node whose children do not consist of exactly one element node and zero or more comment and processing instruction nodes, in any order.

err:XQDY0064

It is a dynamic error if the value of the name expression in a computed processing instruction constructor is equal to XML (in any combination of upper and lower case).

err:XQST0065

A static error is raised if a Prolog contains more than one ordering mode declaration.

err:XQST0066

A static error is raised if a Prolog contains more than one default element/type namespace declaration, or more than one default function namespace declaration.

err:XQST0067

A static error is raised if a Prolog contains more than one construction declaration.

err:XQST0068

A static error is raised if a Prolog contains more than one boundary-space declaration.

err:XQST0069

A static error is raised if a Prolog contains more than one empty order declaration.

err:XQST0070

A static error is raised if one of the predefined prefixes xml or xmlns appears in a namespace declaration or a default namespace declaration, or if any of the following conditions is statically detected in any expression or declaration:

  • The prefix xml is bound to some namespace URI other than http://www.w3.org/XML/1998/namespace.

  • A prefix other than xml is bound to the namespace URI http://www.w3.org/XML/1998/namespace.

  • The prefix xmlns is bound to any namespace URI.

  • A prefix other than xmlns is bound to the namespace URI http://www.w3.org/2000/xmlns/.

err:XQST0071

A static error is raised if the namespace declaration attributes of a direct element constructor do not have distinct names.

err:XQDY0072

It is a dynamic error if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.

err:XQDY0074

It is a dynamic error if the value of the name expression in a computed element or attribute constructor cannot be converted to an expanded QName (for example, because it contains a namespace prefix not found in statically known namespaces.)

err:XQST0075

An implementation that does not support the Schema Aware Feature must raise a static error if it encounters a validate expression.

err:XQST0076

It is a static error if a collation subclause in an order byor group by clause of a FLWOR expression does not identify a collation that is present in statically known collations.

err:XQST0079

It is a static error if an extension expression contains neither a pragma that is recognized by the implementation nor an expression enclosed in curly braces.

err:XPST0080

It is a static error if the target type of a cast or castable expression is xs:NOTATION, xs:anySimpleType, or xs:anyAtomicType.

err:XPST0081

It is a static error if a QName used in a query contains a namespace prefix that cannot be expanded into a namespace URI by using the statically known namespaces.

err:XQDY0084

It is a dynamic error if the element validated by a validate statement does not have a top-level element declaration in the in-scope element declarations, if validation mode is strict.

err:XQST0085

It is a static error if the namespace URI in a namespace declaration attribute is a zero-length string, and the implementation does not support [XML Names 1.1].

err:XQTY0086

It is a type error if the typed value of a copied element or attribute node is namespace-sensitive when construction mode is preserve and copy-namespaces mode is no-preserve.

err:XQST0087

It is a static error if the encoding specified in a Version Declaration does not conform to the definition of EncName specified in [XML 1.0].

err:XQST0088

It is a static error if the literal that specifies the target namespace in a module import or a module declaration is of zero length.

err:XQST0089

It is a static error if a variable bound in a for or window clause of a FLWOR expression, and its associated positional variable, do not have distinct names (expanded QNames).

err:XQST0090

It is a static error if a character reference does not identify a valid character in the version of XML that is in use.

err:XQDY0091

An implementation MAY raise a dynamic error if an xml:id error, as defined in [XML ID], is encountered during construction of an attribute named xml:id.

err:XQDY0092

An implementation MAY raise a dynamic error if a constructed attribute named xml:space has a value other than preserve or default.

err:XQST0094

The name of each grouping variable must be equal (by the eq operator on expanded QNames) to the name of a variable in the input tuple stream.

err:XQDY0096

It is a dynamic errorif the node-name of a node constructed by a computed element constructor has any of the following properties:

  • Its namespace prefix is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

err:XQST0097

It is a static error for a decimal-format to specify a value that is not valid for a given property, as described in statically known decimal formats

err:XQST0098

It is a static error if, for any named or unnamed decimal format, the properties representing characters used in a picture string do not each have distinct values. The following properties represent characters used in a picture string: decimal-separator, exponent-separator, grouping-separator, percent, per-mille, the family of ten decimal digits starting with zero-digit, digit, and pattern-separator.

err:XQST0099

No module may contain more than one ContextItemDecl.

err:XQDY0101

An error is raised if a computed namespace constructor attempts to do any of the following:

  • Bind the prefix xml to some namespace URI other than http://www.w3.org/XML/1998/namespace.

  • Bind a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • Bind the prefix xmlns to any namespace URI.

  • Bind a prefix to the namespace URI http://www.w3.org/2000/xmlns/.

  • Bind any prefix (including the empty prefix) to a zero-length namespace URI.

err:XQDY0102

In an element constructor, if two or more namespace bindings in the in-scope bindings would have the same prefix, then an error is raised if they have different URIs; if they would have the same prefix and URI, duplicate bindings are ignored.

If the name of an element in an element constructor is in no namespace, creating a default namespace for that element using a computed namespace constructor is an error.

err:XQST0103

All variables in a window clause must have distinct names.

err:XQST0104

A TypeName that is specified in a validate expression must be found in the in-scope schema definitions

err:XQTY0105

It is a type error if the content sequence in an element constructor contains a function .

err:XQST0106

It is a static error if a function declaration contains both a %private and a %public annotation.

err:XQST0108

It is a static error if an output declaration occurs in a library module.

err:XQST0109

It is a static error if the local name of an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace is not one of the serialization parameter names listed in C.1 Static Context Components, or if the name of an output declaration is use-character-maps.

err:XQST0110

It is a static error if the same serialization parameter is used more than once in an output declaration.

err:XQST0111

It is a static error for a query prolog to contain two decimal formats with the same name, or to contain two default decimal formats.

err:XQST0113

Specifying a VarValue or VarDefaultValue for a context item declaration in a library module is a static error.

err:XQST0114

It is a static error for a decimal format declaration to define the same property more than once.

err:XQST0115

It is a static error if the document specified by the option Q{http://www.w3.org/2010/xslt-xquery-serialization}parameter-document raises a serialization error.

err:XQST0116

It is a static errorif a variable declaration contains both a %private and a %public annotation, more than one %private annotation, or more than one %public annotation.

err:XPTY0117

When applying the coercion rules, if an item is of type xs:untypedAtomic and the expected type is namespace-sensitive, a type error [err:XPTY0117] is raised.

err:XQST0118

In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix.

err:XQST0119

It is a static error if the implementation is not able to process the value of an output:parameter-document declaration to produce an XDM instance.

err:XQST0125

It is a static error if an inline function expression is annotated as %public or %private.

err:XPDY0130

An implementation-dependent limit has been exceeded.

err:XQST0134

The namespace axis is not supported.

err:XQDY0137

No two keys in a map may have the same key value.

err:XQST0140

It is a static error if a named item type declaration is recursive, unless it satisfies the conditions defined in 3.2.8.4 Recursive Record Types.

err:XPTY0141

In a forclause, when the keyword member is present, the value of the binding collection must be a single array; and when either or both of the keywords key and value are present, the value of the binding collection must be a single map.

err:XPTY0144

During the analysis phase, an axis step is classified as implausible if the combination of the inferred context item type, the choice of axis, and the supplied node test, is such that the axis step will always return an empty sequence.

err:XPTY0145

During the analysis phase, a unary or postfix lookup expression is classified as implausible if the combination of the inferred type of the left-hand operand (or the context item type in the case of a unary expression) and the choice of key specifier is such that the lookup expression will always return an empty sequence.

err:XQST0146

It is a static error if two or more item types declared or imported by a module have equal expanded QNames (as defined by the eq operator.)

err:XQST0148

It is a static error if an optional parameter in a function declaration is followed by a parameter that does not have a default value.

err:XQST0149

It is a static error if the schemas imported by different modules of a query are not compatible as defined in Section 2.8.1 Schema ConsistencyDM.

err:XQST0151

It is a static error if a node name supplied as a string literal in a computed element or attribute constructor does not take the form of an EQName.

G The application/xquery Media Type

This Appendix specifies the media type for XQuery Version 1.0. XQuery is a language for querying over collections of data from XML data sources, as specified in the main body of this document. This media type is being submitted to the IESG (Internet Engineering Steering Group) for review, approval, and registration with IANA (Internet Assigned Numbers Authority.)

G.1 Introduction

This document, found at http://www.w3.org/TR/xquery/, together with its normative references, defines the language XQuery Version 1.0. This Appendix provides information about the application/xquery media type, which is intended to be used for transmitting queries written in the XQuery language.

This document was prepared by members of the W3C XML Query Working Group. Please send comments to public-qt-comments@w3.org, a public mailing list with archives at http://lists.w3.org/Archives/Public/public-qt-comments.

G.2 Registration of MIME Media Type application/xquery

MIME media type name: application

MIME subtype name: xquery

Required parameters: none

Optional parameters: none

The syntax of XQuery is expressed in Unicode but may be written with any Unicode-compatible character encoding, including UTF-8 or UTF-16, or transported as US-ASCII or ISO-8859-1 with Unicode characters outside the range of the given encoding represented using an XML-style &#xddd; syntax.

G.2.1 Interoperability Considerations

None known.

G.2.2 Applications Using this Media Type

The public XQuery Web page lists more than two dozen implementations of the XQuery language, both proprietary and open source.

This media type is registered to allow for deployment of XQuery on the World Wide Web.

G.2.3 File Extensions

The most common file extensions in use for XQuery are .xq and .xquery.

The appropriate Macintosh file type code is TEXT.

G.2.4 Intended Usage

The intended usage of this media type is for interchange of XQuery expressions.

G.2.5 Author/Change Controller

XQuery was produced by, and is maintained by, the World Wide Web Consortium’s XML Query Working Group. The W3C has change control over this specification.

G.3 Encoding Considerations

For use with transports that are not 8-bit clean, quoted-printable encoding is recommended since the XQuery syntax itself uses the US-ASCII-compatible subset of Unicode.

An XQuery document may contain an encoding declaration as part of its version declaration:

xquery version "3.1" encoding "utf-8";

G.4 Recognizing XQuery Files

An XQuery file may have the string xquery version "V.V" near the beginning of the document, where "V.V" is a version number. Currently the version number, if present, must be "1.0", "3.0", or "3.1".

G.5 Charset Default Rules

XQuery documents use the Unicode character set and, by default, the UTF-8 encoding.

G.6 Security Considerations

Queries written in XQuery may cause arbitrary URIs or IRIs to be dereferenced. Therefore, the security issues of [RFC3987] Section 8 should be considered. In addition, the contents of resources identified by file: URIs can in some cases be accessed, processed and returned as results. XQuery expressions can invoke any of the functions defined in [XQuery and XPath Functions and Operators 4.0]. For example, the fn:doc() and fn:doc-available() functions allow local filesystem probes as well as access to any URI-defined resource accessible from the system evaluating the XQuery expression. The fn:transform() function allows calls to URI-identified XSLT transformations which may in turn call external extension functions and access or write to the file system. The fn:transform() function should be sandboxed or disabled if untrusted queries are run.

XQuery is a full declarative programming language, and supports user-defined functions, external function libraries (modules) referenced by URI, and system-specific “native” functions.

Arbitrary recursion is possible, as is arbitrarily large memory usage, and implementations may place limits on CPU and memory usage, as well as restricting access to system-defined functions.

The optional XQuery Update Facility allows XQuery expressions to create and update persistent data, potentially including writing to arbitrary locations on the local filesystem as well as to remote URIs. Untrusted queries should not be given write access to data.

Furthermore, because the XQuery language permits extensions, it is possible that application/xquery may describe content that has security implications beyond those described here.

H Glossary (Non-Normative)

anonymous function

An anonymous function is a function item with no name. Anonymous functions may be created, for example, by evaluating an inline function expression or by partial function application.

application function

Application functions are function definitions written in a host language such as XQuery or XSLT whose syntax and semantics are defined in this family of specifications. Their behavior (including the rules determining the static and dynamic context) follows the rules for such functions in the relevant host language specification.

argument expression

An argument to a function call is either an argument expression or an ArgumentPlaceholder (?); in both cases it may either be supplied positionally, or identified by a name (called a keyword).

arity range

A function definition has an arity range, which is a range of consecutive non-negative integers. If the function definition has M required parameters and N optional parameters, then its arity range is from M to M+N inclusive.

array

An array is a function item that associates a set of positions, represented as positive integer keys, with values.

associated value

The value associated with a given key is called the associated value of the key.

atomic item

An atomic item is a value in the value space of an atomic type, as defined in [XML Schema 1.0] or [XML Schema 1.1].

atomic type

An atomic type is a simple schema type whose {variety} is atomic.

atomization

Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.1.4 fn:dataFO.

available documents

Available documents. This is a mapping of strings to document nodes. Each string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.

available item collections

Available collections. This is a mapping of strings to sequences of items. Each string represents the absolute URI of a resource. The sequence of items represents the result of the fn:collection function when that URI is supplied as the argument.

available text resources

Available text resources. This is a mapping of strings to text resources. Each string represents the absolute URI of a resource. The resource is returned by the fn:unparsed-text function when applied to that URI.

available uri collections

Available URI collections. This is a mapping of strings to sequences of URIs. The string represents the absolute URI of a resource which can be interpreted as an aggregation of a number of individual resources each of which has its own URI. The sequence of URIs represents the result of the fn:uri-collection function when that URI is supplied as the argument.

axis step

An axis step returns a sequence of nodes that are reachable from a starting node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type annotation .

base URI declaration

A base URI declaration specifies the Static Base URI property. The Static Base URI property is used when resolving relative URI references.

binary

In the operator mapping tables, the term binary refers to the types xs:hexBinary and xs:base64Binary.

binding collection

In a for clause, when an expression is preceded by the keyword in, the value of that expression is called a binding collection.

binding sequence

In a window clause, when an expression is preceded by the keyword in, the value of that expression is called a binding sequence.

boundary-space declaration

A boundary-space declaration sets the boundary-space policy in the static context, overriding any implementation-defined default. Boundary-space policy controls whether boundary whitespace is preserved by element constructors during processing of the query.

boundary-space policy

Boundary-space policy. This component controls the processing of boundary whitespace by direct element constructors, as described in 4.12.1.4 Boundary Whitespace.

boundary whitespace

Boundary whitespace is a sequence of consecutive whitespace characters within the content of a direct element constructor, that is delimited at each end either by the start or end of the content, or by a DirectConstructor, or by an EnclosedExpr. For this purpose, characters generated by character references such as &#x20; or by CDataSections are not considered to be whitespace characters.

character reference

A character reference is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal codepoint.

choice item type

A choice item type defines an item type that is the union of a number of alternatives. For example the type (xs:hexBinary | xs:base64Binary) defines the union of these two primitive atomic types, while the type (map(*) | array(*)) matches any item that is either a map or an array.

coercion rules

The coercion rules are rules used to convert a supplied value to a required type, for example when converting an argument of a function call to the declared type of the function parameter.

collation

A collation is a specification of the manner in which strings and URIs are compared and, by extension, ordered. For a more complete definition of collation, see Section 5.3 Comparison of stringsFO.

comma operator

One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.

complex terminal

A complex terminal is a variable terminal whose production rule references, directly or indirectly, an ordinary production rule.

computed element constructor

A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.

construction declaration

A construction declaration sets the construction mode in the static context, overriding any implementation-defined default.

construction mode

Construction mode. The construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xs:untyped; all element nodes copied during node construction receive the type xs:untyped, and all attribute nodes copied during node construction receive the type xs:untypedAtomic.

constructor function

The constructor function for a given simple type is used to convert instances of other simple types into the given type. The semantics of the constructor function call T($arg) are defined to be equivalent to the expression $arg cast as T?.

content expression

In an enclosed expression, the optional expression enclosed in curly brackets is called the content expression.

context dependent

A function definition is said to be context dependent if its result depends on the static or dynamic context of its caller. A function definition may be context-dependent for some arities in its arity range, and context-independent for others: for example fn:name#0 is context-dependent while fn:name#1 is context-independent.

context node

When the context value is a single item, it can also be referred to as the context item; when it is a single node, it can also be referred to as the context node.

context position

The context position is the position of the context value within the series of values currently being processed.

context size

The context size is the number of values in the series of values currently being processed.

context value

The context value is the value currently being processed.

copy-namespaces declaration

A copy-namespaces declaration sets the value of copy-namespaces mode in the static context, overriding any implementation-defined default. Copy-namespaces mode controls the namespace bindings that are assigned when an existing element node is copied by an element constructor or document constructor.

copy-namespaces mode

Copy-namespaces mode. This component controls the namespace bindings that are assigned when an existing element node is copied by an element constructor, as described in 4.12.1 Direct Element Constructors. Its value consists of two parts: preserve or no-preserve, and inherit or no-inherit.

current dateTime

Current dateTime. This information represents an implementation-dependent point in time during the processing of a query , and includes an explicit timezone. It can be retrieved by the fn:current-dateTime function. If called multiple times during the execution of a query , this function always returns the same result.

data model

XQuery 4.0 operates on the abstract, logical structure of an XML document or JSON object rather than its surface syntax. This logical structure, known as the data model, is defined in [XQuery and XPath Data Model (XDM) 4.0].

decimal-format declaration

A decimal format declaration adds a decimal format to the statically known decimal formats, which define the properties used to format numbers using the fn:format-number() function

decimal-separator

decimal-separator(M, R) is used to separate the integer part of the number from the fractional part. The default value for both the marker and the rendition is U+002E (FULL STOP, PERIOD, .) .

default calendar

Default calendar. This is the calendar used when formatting dates in human-readable output (for example, by the functions fn:format-date and fn:format-dateTime) if no other calendar is requested. The value is a string.

default collation

Default collation. This identifies one of the collations in statically known collations as the collation to be used by functions and operators for comparing and ordering values of type xs:string and xs:anyURI (and types derived from them) when no explicit collation is specified.

default collation declaration

A default collation declaration sets the value of the default collation in the static context, overriding any implementation-defined default.

default collection

Default collection. This is the sequence of items that would result from calling the fn:collection function with no arguments.

default function namespace

Default function namespace. This is either a namespace URI, or absentDM. The namespace URI, if present, is used for any unprefixed QName appearing in a position where a function name is expected.

default language

Default language. This is the natural language used when creating human-readable output (for example, by the functions fn:format-date and fn:format-integer) if no other language is requested. The value is a language code as defined by the type xs:language.

default namespace for elements and types

Default namespace for elements and types. This is either a namespace URI, or the special value "##any", or absentDM. This indicates how unprefixed QNames are interpreted when they appear in a position where an element name or type name is expected.

default order for empty sequences

Default order for empty sequences. This component controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression, as described in 4.13.9 Order By Clause.

default place

Default place. This is a geographical location used to identify the place where events happened (or will happen) when processing dates and times using functions such as fn:format-date, fn:format-dateTime, and fn:civil-timezone, if no other place is specified. It is used when translating timezone offsets to civil timezone names, and when using calendars where the translation from ISO dates/times to a local representation is dependent on geographical location. Possible representations of this information are an ISO country code or an Olson timezone name, but implementations are free to use other representations from which the above information can be derived. The only requirement is that it should uniquely identify a civil timezone, which means that country codes for countries with multiple timezones, such as the United States, are inadequate.

default URI collection

Default URI collection. This is the sequence of URIs that would result from calling the fn:uri-collection function with no arguments.

delimiting terminal symbol

The delimiting terminal symbols are: !!=#$%()**:,-...::*:::=;<<<===!>=>=?>>>=>>????[@[]```{{{|||}}}×÷AposStringLiteralBracedURILiteral]]><![CDATA[--><!--/></<+#)(#?><?QuotStringLiteralS///]````[}``{StringLiteral

depends on

A variable value (or the context value) depends on another variable value (or the context value) if, during the evaluation of the initializing expression of the former, the latter is accessed through the module context.

digit

digit(M) is a character used in the picture string to represent an optional digit; the default value is U+0023 (NUMBER SIGN, #) .

direct element constructor

A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.

document order

Informally, document order is the order in which nodes appear in the XML serialization of a document.

dynamically known function definitions

Dynamically known function definitions. This is a set of function definitions. It includes the statically known function definitions as a subset, but may include other function definitions that are not known statically.

dynamic context

The dynamic context of an expression is defined as information that is needed for the dynamic evaluation of an expression, beyond any information that is needed from the static context.

dynamic error

A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase.

dynamic evaluation phase

The dynamic evaluation phase is the phase during which the value of an expression is computed.

dynamic function call

A dynamic function call consists of a base expression that returns the function and a parenthesized list of zero or more arguments (argument expressions or ArgumentPlaceholders).

dynamic function call

A dynamic function call is an expression that is evaluated by calling a function item, which is typically obtained dynamically.

dynamic type

Every value matches one or more sequence types. A value is said to have a dynamic typeT if it matches (or is an instance of) the sequence type T.

effective boolean value

The effective boolean value of a value is defined as the result of applying the fn:boolean function to the value, as defined in Section 7.3.1 fn:booleanFO.

effective case

The effective case of a switch expression is the first case clause that matches, using the rules given above, or the default clause if no such case clause exists.

effective case

The effective case in a typeswitch expression is the first case clause in which the value of the operand expression matches a SequenceType in the SequenceTypeUnion of the case clause, using the rules of SequenceType matching.

empty order declaration

An empty order declaration sets the default order for empty sequences in the static context, overriding any implementation-defined default. This declaration controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression.

empty sequence

A sequence containing zero items is called an empty sequence.

enclosed expression

An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly brackets.

encoding declaration

If present, a version declaration may optionally include an encoding declaration. The value of the string literal following the keyword encoding is an encoding name, and must conform to the definition of EncName specified in [XML 1.0] [err:XQST0087]. The purpose of an encoding declaration is to allow the writer of a query to provide a string that indicates how the query is encoded, such as "UTF-8", "UTF-16", or "US-ASCII".

entry

Each key / value pair in a map is called an entry.

enumeration type

An EnumerationType accepts a fixed set of string values.

environment variables

Environment variables. This is a mapping from names to values. Both the names and the values are strings. The names are compared using an implementation-defined collation, and are unique under this collation. The set of environment variables is implementation-defined and may be empty.

equivalent grouping keys

Two tuples T1 and T2 have equivalent grouping keys if and only if, for each grouping variable GV, the atomized value of GV in T1 is deep-equal to the atomized value of GV in T2, as defined by applying the function fn:deep-equal using the appropriate collation.

error value

In addition to its identifying QName, a dynamic error may also carry a descriptive string and one or more additional values called error values.

Executable Base URI

Executable Base URI. This is an absolute URI used to resolve relative URIs during the evaluation of expressions; it is used, for example, to resolve a relative URI supplied to the fn:doc or fn:unparsed-text functions.

expanded QName

An expanded QName is a triple: its components are a prefix, a local name, and a namespace URI. In the case of a name in no namespace, the namespace URI and prefix are both absent. In the case of a name in the default namespace, the prefix is absent.

exponent-separator

exponent-separator(M, R) is used to separate the mantissa from the exponent in scientific notation. The default value for both the marker and the rendition is U+0065 (LATIN SMALL LETTER E, e) .

expression context

The expression context for a given expression consists of all the information that can affect the result of the expression.

extension expression

An extension expression is an expression whose semantics are implementation-defined.

external function

External functions can be characterized as functions that are neither part of the processor implementation, nor written in a language whose semantics are under the control of this family of specifications. The semantics of external functions, including any context dependencies, are entirely implementation-defined. In XSLT, external functions are called Section 24.1 Extension Functions XT30.

filter expression

A filter expression is an expression in the form E1[E2]: its effect is to return those items from the value of E1 that satisfy the predicate in E2.

fixed focus

A fixed focus is a focus for an expression that is evaluated once, rather than being applied to a series of values; in a fixed focus, the context value is set to one specific value, the context position is 1, and the context size is 1.

focus

The first three components of the dynamic context (context value, context position, and context size) are called the focus of the expression.

focus function

A focus function is an inline function expression in which the function signature is implicit: the function takes a single argument of type item()* (that is, any value), and binds this to the context value when evaluating the function body, which returns a result of type item()*.

function assertion

A function assertion is a predicate that restricts the set of functions matched by a FunctionType. It uses the same syntax as 5.15 Annotations.

function coercion

Function coercion wraps a function item in a new function whose signature is the same as the expected type. This effectively delays the checking of the argument and return types until the function is called.

function definition

A function definition contains information used to evaluate a static function call, including the name, parameters, and return type of the function.

function item

A function item is an item that can be called using a dynamic function call.

generalized atomic type

A generalized atomic type is an item type whose instances are all atomic items. Generalized atomic types include (a) atomic types, either built-in (for example xs:integer) or imported from a schema, (b) pure union types, either built-in (xs:numeric and xs:error) or imported from a schema, (c) choice item types if their alternatives are all generalized atomic types, and (d) enumeration types.

Gregorian

In the operator mapping tables, the term Gregorian refers to the types xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gDay, and xs:gMonth.

grouping key

The atomized value of a grouping variable is called a grouping key.

grouping-separator

grouping-separator(M, R) is used to separate groups of digits (for example as a thousands separator). The default value for both the marker and the rendition is U+002C (COMMA, ,) .

grouping variable

Each grouping specification specifies one grouping variable, which refers to variable bindings in the pre-grouping tuples. The values of the grouping variables are used to assign pre-grouping tuples to groups.

guarded

An expression E is said to be guarded by some governing condition C if evaluation of E is not allowed to fail with a dynamic error except when C applies.

ignorable whitespace

Ignorable whitespace consists of any whitespace characters that may occur between terminals, unless these characters occur in the context of a production marked with a ws:explicit annotation, in which case they can occur only where explicitly specified (see A.3.5.2 Explicit Whitespace Handling).

implausible

Certain expressions, while not erroneous, are classified as being implausible, because they achieve no useful effect.

implementation defined

Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementer for each particular implementation.

implementation dependent

Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementer for any particular implementation.

implicit timezone

Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or arithmetic operation. The implicit timezone is an implementation-defined value of type xs:dayTimeDuration. See Section 3.2.7.3 Timezones XS1-2 or Section 3.3.7 dateTime XS11-2 for the range of valid values of a timezone.

infinity

infinity(R) is the string used to represent the double value infinity (INF); the default value is the string "Infinity"

initial context value

In the dynamic context of every module in a query, the context value component must have the same setting. If this shared setting is not absentDM, it is referred to as the initial context value.

initializing expression

If a variable declaration includes an expression (VarValue or VarDefaultValue), the expression is called an initializing expression. The static context for an initializing expression includes all functions, variables, and namespaces that are declared or imported anywhere in the Prolog.

inline function expression

An inline function expression, when evaluated, creates an anonymous function defined directly in the inline function expression.

in-scope attribute declarations

In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration). If the Schema Aware Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.

in-scope element declarations

In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration). If the Schema Aware Feature is supported, in-scope element declarations include all element declarations found in imported schemas.

in-scope named item types

In-scope named item types. This is a mapping from expanded QName to named item types.

in-scope namespaces

The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI.

in-scope schema definitions

In-scope schema definitions is a generic term for all the element declarations, attribute declarations, and schema type definitions that are in scope during static analysis of an expression.

in-scope schema type

In-scope schema types. Each schema type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope schema types include the predefined schema types described in 3.5 Schema Types. If the Schema Aware Feature is supported, in-scope schema types also include all type definitions found in imported schemas.

in-scope variables

In-scope variables. This is a mapping from expanded QName to type. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.

item

An item is either an atomic item, a node, or a function item.

item type

An item type is a type that can be expressed using the ItemType syntax, which forms part of the SequenceType syntax. Item types match individual items.

item type designator

An item type designator is a syntactic construct conforming to the grammar rule ItemType. An item type designator is said to designate an item type.

kind test

An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.

lexical QName

A lexical QName is a name that conforms to the syntax of the QName production

library module

A module that does not contain a Query Body is called a library module. A library module consists of a module declaration followed by a Prolog.

literal

A literal is a direct syntactic representation of an atomic item.

literal terminal

A literal terminal is a token appearing as a string in quotation marks on the right-hand side of an ordinary production rule.

main module

A main module consists of a Prolog followed by a Query Body.

map

A map is a function that associates a set of keys with values, resulting in a collection of key / value pairs.

mapping arrow operator

The mapping arrow operator=!> applies a function to each item in a sequence.

may

MAY means that an item is truly optional.

member

The values of an array are called its members.

minus-sign

minus-sign(R) is the string used to mark negative numbers; the default value is U+002D (HYPHEN-MINUS, -) .

module

A module is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.3.3 Expression Processing. Each module is either a main module or a library module.

module declaration

A module declaration serves to identify a module as a library module. A module declaration begins with the keyword module and contains a namespace prefix and a URILiteral.

module feature

The Module Feature allows a query Prolog to contain a Module Import and allows library modules to be created.

module import

A module import imports the public variable declarations, public function declarations, and public item type declarations from one or more library modules into the statically known function definitions, in-scope variables, or in-scope named item types of the importing module.

must

MUST means that the item is an absolute requirement of the specification.

must not

MUST NOT means that the item is an absolute prohibition of the specification.

named function reference

A named function reference is an expression (written name#arity) which evaluates to a function item, the details of the function item being based on the properties of a function definition in the static context.

named item type

A named item type is an ItemType identified by an expanded QName.

name expression

When an expression is used to specify the name of a constructed node, that expression is called the name expression of the constructor.

namespace declaration

A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.

namespace declaration attribute

A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix (including the zero-length prefix) for the constructed element node, including its attributes.

namespace-sensitive

The namespace-sensitive types are xs:QName, xs:NOTATION, types derived by restriction from xs:QName or xs:NOTATION, list types that have a namespace-sensitive item type, and union types with a namespace-sensitive type in their transitive membership.

name test

A node test that consists only of an EQName or a Wildcard is called a name test.

NaN

NaN(R) is the string used to represent the double value NaN (not a number); the default value is the string "NaN"

node

A node is an instance of one of the node kinds defined in Section 5 NodesDM.

node test

A node test is a condition on the name, kind (element, attribute, text, document, comment, or processing instruction), and/or type annotation of a node. A node test determines which nodes contained by an axis are selected by a step.

non-delimiting terminal symbol

The non-delimiting terminal symbols are: allowingancestorancestor-or-selfandarrayasatattributebase-uriboundary-spacebycasecastcastablecatchchildcollationcommentconstructioncontextcopy-namespacescountdecimal-formatdecimal-separatordeclaredefaultdescendantdescendant-or-selfdigitdivdocumentdocument-nodeelementelseemptyempty-sequenceencodingendenumeqeveryexceptexponent-separatorfalsefixedfnfollowingfollowing-or-selffollowing-siblingfollowing-sibling-or-selfforfunctiongegroupgrouping-separatorgtidivifimportininfinityinheritinstanceintersectisitemitemskeykeyslaxleletltmapmemberminus-signmodmodulenamespacenamespace-nodeNaNnenextno-inheritno-preservenodeofonlyoptionororderorderedorderingotherwisepairsparentpattern-separatorper-millepercentprecedingpreceding-or-selfpreceding-sibling-or-selfpreservepreviousprocessing-instructionrecordreturnsatisfiesschemaschema-attributeschema-elementselfslidingsomestablestartstrictstripswitchtextthentotreattruetrytumblingtypetypeswitchunionunorderedvalidatevaluevaluesvariableversionwhenwherewhilewindowxqueryzero-digitascendingBinaryIntegerLiteralDecimalLiteraldescendingDoubleLiteralexternalgreatestHexIntegerLiteralIntegerLiteralleastNCNameQNameURIQualifiedName

numeric

When referring to a type, the term numeric denotes the types xs:integer, xs:decimal, xs:float, and xs:double which are all member types of the built-in union type xs:numeric.

numeric predicate

A predicate whose predicate expression returns a value of type xs:numeric+ is called a numeric predicate.

operator function

For each operator and valid combination of operand types, the operator mapping tables specify a result type and an expression that invokes an operator function; the operator function implements the semantics of the operator for the given types.

option declaration

An option declaration declares an option that affects the behavior of a particular implementation. Each option consists of an identifying EQName and a StringLiteral.

ordinary production rule

An ordinary production rule is a production rule in A.1 EBNF that is not annotated ws:explicit.

output declaration

An output declaration is an option declaration in the namespace http://www.w3.org/2010/xslt-xquery-serialization; it is used to declare serialization parameters.

partial function application

A static or dynamic function call is a partial function application if one or more arguments is an ArgumentPlaceholder.

partially applied function

A partially applied function is a function created by partial function application.

path expression

A path expression consists of a series of one or more steps, separated by / or //, and optionally beginning with / or //. A path expression is typically used to locate nodes within trees.

pattern-separator

pattern-separator(M) is a character used to separate positive and negative sub-pictures in a picture string; the default value is U+003B (SEMICOLON, ;) .

percent

percent(M, R) is used to indicate that the number is written as a per-hundred fraction; the default value for both the marker and the rendition is U+0025 (PERCENT SIGN, %) .

per-mille

per-mille(M, R) is used to indicate that the number is written as a per-thousand fraction; the default value for both the marker and the rendition is U+2030 (PER MILLE SIGN, ) .

positional variable

A positional variable is a variable that is preceded by the keyword at.

pragma

A pragma is denoted by the delimiters (# and #), and consists of an identifying EQName followed by implementation-defined content.

predefined entity reference

A predefined entity reference is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance.

predicate truth value

The predicate truth value of a value $V is the result of the expression if ($V instance of xs:numeric+) then ($V = position()) else fn:boolean($V).

primary expression

Primary expressions are the basic primitives of the language. They include literals, variable references, context value references, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.

principal node kind

Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.

private function

A private function is a function with a %private annotation. A private function is hidden from module import, which can not import it into the statically known function definitions of another module.

private item type

A private item type is a named item type with a %private annotation. A private item type is hidden from module import, which can not import it into the in-scope named item types of another module.

private variable

A private variable is a variable with a %private annotation. A private variable is hidden from module import, which can not import it into the in-scope variables of another module.

Prolog

A Prolog is a series of declarations and imports that define the processing environment for the module that contains the Prolog.

public function

A public function is a function without a %private annotation. A public function is accessible to module import, which can import it into the statically known function definitions of another module.

public item type

A public item type is an item type declaration without a %private annotation. A public item type is accessible to module import, which can import it into the in-scope named item types of another module.

public variable

A public variable is a variable without a %private annotation. A public variable is accessible to module import, which can import it into the in-scope variables of another module. Using %public and %private annotations in a main module is not an error, but it does not affect module imports, since a main module cannot be imported. It is a static error [err:XQST0116] if a variable declaration contains both a %private and a %public annotation, more than one %private annotation, or more than one %public annotation.

pure union type

A pure union type is a simple type that satisfies the following constraints: (a) {variety} is union, (b) the {facets} property is empty, (c) no type in the transitive membership of the union type has {variety}list, and (d) no type in the transitive membership of the union type is a type with {variety}union having a non-empty {facets} property

query

A query consists of one or more modules.

query body

The Query Body, if present, consists of an expression that defines the result of the query.

reserved namespaces

A reserved namespace is a namespace that must not be used in the name of a function declaration.

resolve

To resolve a relative URI$rel against a base URI $base is to expand it to an absolute URI, as if by calling the function fn:resolve-uri($rel, $base).

reverse document order

The node ordering that is the reverse of document order is called reverse document order.

same key

Two atomic items K1 and K2 have the same key value if fn:atomic-equal(K1, K2) returns true, as specified in Section 13.2.1 fn:atomic-equalFO

schema aware feature

The Schema Aware Feature permits the query Prolog to contain a schema import, and permits a query to contain a validate expression (see 4.24 Validate Expressions).

schema import

A schema import imports the element declarations, attribute declarations, and type definitions from a schema into the in-scope schema definitions. For each named user-defined simple type in the schema, schema import also adds a corresponding constructor function.

schema type

A schema type is a complex type or simple type as defined in the [XML Schema 1.0] or [XML Schema 1.1] specifications, including built-in types as well as user-defined types.

sequence

A sequence is an ordered collection of zero or more items.

sequence arrow operator

The sequence arrow operator=> applies a function to a supplied sequence.

sequence concatenation

The sequence concatenation of a number of sequences S1, S2, ... Sn is defined to be the sequence formed from the items of S1, followed by the items from S2, and so on, retaining order.

sequence type

A sequence type is a type that can be expressed using the SequenceType syntax. Sequence types are used whenever it is necessary to refer to a type in an XQuery 4.0 expression. The term sequence type suggests that this syntax is used to describe the type of an XQuery 4.0 value, which is always a sequence.

sequence type designator

A sequence type designator is a syntactic construct conforming to the grammar rule SequenceType. A sequence type designator is said to designate a sequence type.

SequenceType matching

SequenceType matching compares a value with an expected sequence type.

serialization

Serialization is the process of converting an XDM instance to a sequence of octets (step DM4 in Figure 1.), as described in [XSLT and XQuery Serialization 4.0].

serialization feature

The Serialization Feature provides means for serializing the result of a query as specified in 2.3.5 Serialization.

setter

Setters are declarations that set the value of some property that affects query processing, such as construction mode or default collation.

should

SHOULD means that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.

singleton

A sequence containing exactly one item is called a singleton.

singleton focus

A singleton focus is a fixed focus in which the context value is a singleton item.

stable

Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query , even if this order is implementation-dependent.

statically known collations

Statically known collations. This is an implementation-defined mapping from URI to collation. It defines the names of the collations that are available for use in processing queries and expressions.

statically known decimal formats

Statically known decimal formats. This is a mapping from QNames to decimal formats, with one default format that has no visible name, referred to as the unnamed decimal format. Each format is available for use when formatting numbers using the fn:format-number function.

statically known function definitions

Statically known function definitions. This is a set of function definitions.

statically known namespaces

Statically known namespaces. This is a mapping from prefix to namespace URI that defines all the namespaces that are known during static processing of a given expression.

static analysis phase

The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).

Static Base URI

Static Base URI. This is an absolute URI, used to resolve relative URIs during static analysis.

static context

The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.

static error

An error that can be detected during the static analysis phase, and is not a type error, is a static error.

static function call

A static function call consists of an EQName followed by a parenthesized list of zero or more arguments.

static type

The static type of an expression is the best inference that the processor is able to make statically about the type of the result of the expression.

step

A step is a part of a path expression that generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates, working from left to right. A step may be either an axis step or a postfix expression.

string constructor

A String Constructor creates a string from literal text and interpolated expressions.

string value

The string value of a node is a string and can be extracted by applying the Section 2.1.3 fn:stringFO function to the node.

substantively disjoint

Two sequence types are deemed to be substantively disjoint if (a) neither is a subtype of the other (see 3.3.1 Subtypes of Sequence Types) and (b) the only values that are instances of both types are one or more of the following:

  • The empty sequence, ().

  • The empty map, {}.

  • The empty array, [].

substitution group

Substitution groups are defined in Section 2.2.2.2 Element Substitution Group XS1-1 and Section 2.2.2.2 Element Substitution Group XS11-1. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.

subtype

Given two sequence types or item types, the rules in this section determine if one is a subtype of the other. If a type A is a subtype of type B, it follows that every value matched by A is also matched by B.

subtype substitution

The use of a value that has a dynamic type that is a subtype of the expected type is known as subtype substitution.

symbol

Each rule in the grammar defines one symbol, using the following format:

symbol ::= expression
symbol separators

Whitespace and Comments function as symbol separators. For the most part, they are not mentioned in the grammar, and may occur between any two terminal symbols mentioned in the grammar, except where that is forbidden by the /* ws: explicit */ annotation in the EBNF, or by the /* xgc: xml-version */ annotation.

system function

System functions include the functions defined in [XQuery and XPath Functions and Operators 4.0], functions defined by the specifications of a host language, constructor functions for atomic types, and any additional functions provided by the implementation. System functions are sometimes called built-in functions.

target namespace

The target namespace of a module is the namespace of the objects (such as elements or functions) that it defines.

terminal

A terminal is a symbol or string or pattern that can appear in the right-hand side of a rule, but never appears on the left-hand side in the main grammar, although it may appear on the left-hand side of a rule in the grammar for terminals.

tuple

A tuple is a set of zero or more named variables, each of which is bound to a value that is an XDM instance.

tuple stream

A tuple stream is an ordered sequence of zero or more tuples.

type annotation

Each element node and attribute node in an XDM instance has a type annotation (described in Section 2.8 Schema InformationDM). The type annotation of a node is a reference to a schema type.

typed data feature

The Typed Data Feature permits an XDM instance to contain element node types other than xs:untyped and attributes node types other than xs:untypedAtomic.

type declaration

A variable binding may be accompanied by a type declaration, which consists of the keyword as followed by the static type of the variable, declared using the syntax in 3.1 Sequence Types.

typed value

The typed value of a node is a sequence of atomic items and can be extracted by applying the Section 2.1.4 fn:dataFO function to the node.

type error

A type error may be raised during the static analysis phase or the dynamic evaluation phase. During the static analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the dynamic evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.

type promotion

Under certain circumstances, an atomic item can be promoted from one type to another.

URI

Within this specification, the term URI refers to a Universal Resource Identifier as defined in [RFC3986] and extended in [RFC3987] with the new name IRI.

user-defined function

User defined functions are functions that contain a function body, which provides the implementation of the function as a content expression.

value

In the data model, a value is always a sequence.

variable declaration

A variable declaration in the XQuery prolog defines the name and static type of a variable, and optionally a value for the variable. It adds to the in-scope variables in the static context, and may also add to the variable values in the dynamic context.

variable reference

A variable reference is an EQName preceded by a $-sign.

variable terminal

A variable terminal is an instance of a production rule that is not itself an ordinary production rule but that is named (directly) on the right-hand side of an ordinary production rule.

variable values

Variable values. This is a mapping from expanded QName to value. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.

version declaration

A version declaration can identify the applicable XQuery syntax and semantics for a module, as well as its encoding.

warning

In addition to static errors, dynamic errors, and type errors, an XQuery 4.0 implementation may raise warnings, either during the static analysis phase or the dynamic evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.

whitespace

A whitespace character is any of the characters defined by [http://www.w3.org/TR/REC-xml/#NT-S].

wildcard-matches

In these rules, if MU and NU are NameTestUnions, then MUwildcard-matchesNU is true if every name that matches MU also matches NU.

window

A window is a sequence of consecutive items drawn from the binding sequence.

XDM instance

The term XDM instance is used, synonymously with the term value, to denote an unconstrained sequence of items.

XPath 1.0 compatibility mode

XPath 1.0 compatibility mode.This component must be set by all host languages that include XPath 3.1 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false.

XQuery 1.0 Processor

An XQuery 1.0 Processor processes a query according to the XQuery 1.0 specification.

XQuery 3.0 Processor

An XQuery 3.0 Processor processes a query according to the XQuery 3.0 specification.

XQuery 3.1 Processor

An XQuery 3.1 Processor processes a query according to the XQuery 3.1 specification.

XQuery 4.0 Processor

An XQuery 4.0 Processor processes a query according to the XQuery 4.0 specification.

XQuery version number

An XQuery version number consists of two integers, referred to as the major version number and the minor version number.

xs:anyAtomicType

xs:anyAtomicType is an atomic type that includes all atomic items (and no values that are not atomic). Its base type is xs:anySimpleType from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as xs:decimal and xs:string, have xs:anyAtomicType as their base type.

xs:dayTimeDuration

xs:dayTimeDuration is derived by restriction from xs:duration. The lexical representation of xs:dayTimeDuration is restricted to contain only day, hour, minute, and second components.

xs:error

xs:error is a simple type with no value space. It is defined in Section 3.16.7.3 xs:error XS11-1 and can be used in the 3.1 Sequence Types to raise errors.

xs:untyped

xs:untyped is used as the type annotation of an element node that has not been validated, or has been validated in skip mode.

xs:untypedAtomic

xs:untypedAtomic is an atomic type that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.

xs:yearMonthDuration

xs:yearMonthDuration is derived by restriction from xs:duration. The lexical representation of xs:yearMonthDuration is restricted to contain only year and month components.

zero-digit

zero-digit(M) is the character used in the picture string to represent the digit zero; the default value is U+0030 (DIGIT ZERO, 0) . This character must be a digit (category Nd in the Unicode property database), and it must have the numeric value zero. This property implicitly defines the ten Unicode characters that are used to represent the values 0 to 9 in the function output: Unicode is organized so that each set of decimal digits forms a contiguous block of characters in numerical sequence. Within the picture string any of these ten character can be used (interchangeably) as a place-holder for a mandatory digit. Within the final result string, these ten characters are used to represent the digits zero to nine.

I Atomic Comparisons: An Overview (Non-Normative)

This appendix provides a non-normative summary of the various functions and operators used for comparison of atomic items, with some background on the history and rationale.

I.1 Equality Comparisons

In XQuery 4.0 there are essentially four ways of comparing two atomic items for equality:

  • $A = $B

    This operator was introduced in XPath 1.0. The semantics were changed slightly in XPath 2.0, but the original semantics remain available when XPath 1.0 compatibility mode is enabled.

    With a general comparison in XPath 2.0 or later (and in XQuery), the following rules are observed:

    • Either operand may be a sequence; the result is true if any pair of items from the two sequences compares equal.

      In consequence, if either operand is an empty sequence, the result is false.

    • If nodes are supplied, they are atomized.

    • Untyped atomic items appearing in one operand are converted to the type of the other operand (if both operands are untyped atomic, they are compared as strings).

    • As a result, the operator is not transitive: the untyped atomic items "4.0" and "4" are not equal to each other, but both compare equal to the integer value 4.

    • Comparison of certain values is context-sensitive. In particular, comparison of strings uses the default collation from the static context, while comparison of date/time values lacking an explicit timezone takes the timezone from the dynamic context.

    • NaN is not equal to NaN; negative zero is equal to positive zero.

    • xs:hexBinary and xs:base64Binary values are mutually comparable: they are equal if they represent the same sequence of octets.

    • Comparing incompatible values (for example xs:integer and xs:date) raises an error.

  • $A eq $B

    Value comparisons were introduced in XPath 2.0 and XQuery 1.0. One of the aims was to make the comparison transitive (a precondition for a wide variety of optimizations), however in edge cases involving comparisons across different numeric types this was not entirely achieved.

    With a value comparison, the rules are:

    • Each operand must either be a single atomic item, or an empty sequence.

    • If either operand is an empty sequence, the result is an empty sequence; in most contexts this has the same effect as returning false.

    • If nodes are supplied, they are atomized.

    • Untyped atomic items are converted to strings (regardless of the type of the other operand).

    • Numeric values of types xs:integer, xs:decimal, or xs:float are converted to xs:double.

      This can lead to problems with implementations of xs:decimal that support more precision than can be held in an xs:double.

    • As with general comparisons, the default collation and implicit timezone are taken from the context.

    • NaN is not equal to NaN; negative zero is equal to positive zero.

    • xs:hexBinary and xs:base64Binary values are mutually comparable: they are equal if they represent the same sequence of octets.

    • Comparing incompatible values (for example xs:integer and xs:date) raises an error.

  • deep-equal($A, $B)

    As the name implies, the deep-equal function was introduced primarily for comparing nodes, or sequences of nodes; however in its simplest form it can also be used to compare two atomic items. The semantics of the comparison used by deep-equal($A, $B) are also invoked by a wide variety of other functions including distinct-values, all-equal, and all-different; it is also used to underpin grouping constructs in both XQuery 4.0 and XSLT 4.0.

    Some of the relevant rules are:

    • Because deep-equal is used to compare sequences, if one of the operands is an empty sequence the result is false; but if both operands are empty sequences, the result is true.

    • If nodes are supplied, they are not atomized; they are compared as nodes.

    • Strings can be compared using the default collation or using an explicitly specified collation; there are also options to compare after normalizing whitespace or unicode.

    • Comparisons of dates and times lacking a timezone uses the implicit timezone from the dynamic context.

    • Numeric values are converted to xs:decimal prior to comparison, not to xs:double. This represents a departure in 4.0 from previous versions of the specification. The conversion must use an implementation of xs:decimal that does not cause loss of precision. As a result, the comparison is now truly transitive, which makes it suitable to underpin grouping operations.

    • To ensure that every value is equal to itself, comparing NaN to NaN returns true.

    • xs:hexBinary and xs:base64Binary values are mutually comparable: they are equal if they represent the same sequence of octets.

    • Comparing incompatible values (for example xs:integer and xs:date) returns false; it does not raise an error.

  • atomic-equal($A, $B)

    This comparison operation was introduced in XPath 3.0 (and XQuery 3.0) for comparing keys in maps; the 4.0 specifications expose it directly as a function that can be called from user applications. The dominant requirements for keys in maps were that the comparison should be transitive, error-free, and context-independent. The relevant rules are:

    • The type signature of the function ensures that it can only be used to compare single items; empty sequences do not arise.

    • If nodes are supplied, they are atomized.

    • Strings are compared codepoint-by-codepoint, without reference to any collation or normalization.

    • Dates and times lacking a timezone are never equal to dates and times that have a timezone. However, when comparing two dates or times that both have a timezone, the timezone is normalized.

    • As with deep-equal, numeric values are converted to xs:decimal prior to comparison, not to xs:double.

    • Comparing NaN to NaN returns true.

    • xs:hexBinary and xs:base64Binary values are distinct: both can co-exist as distinct keys in a map even if the underlying sequence of octets is the same.

    • Comparing incompatible values (for example xs:integer and xs:date) returns false; it does not raise an error.

The following table summarizes these differences. For all these examples it is assumed that (a) the default collation is the HTML case-blind collation, (b) the implicit timezone is +01:00, and (c) nodes are untyped.

$A$B$A = $B$A eq $Bdeep-equal(​$A, $B)atomic-equal(​$A, $B)

()

()

false

()

true

error

12

()

false

()

false

error

(1,2)

(2,3)

true

error

false

error

12

12e0

true

true

true

true

0.2

0.2e0

true

true

false

false

NaN

NaN

false

false

true

true

+0e0

-0e0

true

true

true

true

"A"

"a"

true

true

true

false

"A"

12

error

error

false

false

<a>A</a>

"A"

true

true

false

true

<a>12</a>

12

true

error

false

false

xs:time(​'12:00:00Z')

xs:time(​'13:00:00+01:00')

true

true

true

true

xs:time(​'12:00:00Z')

xs:time(​'13:00:00')

true

true

true

false

xs:hexBinary(​"0000")

xs:base64Binary(​"AAA=")

true

true

true

false

I.2 Ordering Comparisons

In XQuery 4.0 there are essentially three ways of comparing two atomic items for their relative ordering:

  • $A < $B

  • $A lt $B

  • Sorting

TODO: to be expanded.

J Backwards Compatibility (Non-Normative)

J.1 Incompatibilities relative to XQuery 3.1

In fn:format-integer, certain formatting pictures using a circumflex as a grouping separator might be interpreted differently in 4.0: for example format-integer(1234, "9^999") would output "1^234" in 3.1, but will output "1621" (1234 in base 9) with 4.0. As a workaround, this can be rewritten as format-integer(1234, "0^000").

In computed node constructors, the node name must now be written in quotation marks if it matches certain language keywords. For example element div {} must now be written element "div" {}. (Alternatively, element { "div" } {} and element Q{}div {} are permitted by both XQuery 3.1 and XQuery 4.0.) This change is made because {} is now a valid expression representing an empty map, so expressions such as element otherwise {} could (without this rule) be parsed in two different ways.

In XQuery 4.0, certain expressions are classified as implausible: an example is @code/text(), which will always return an empty sequence. A processor may report a static error when such expressions are encountered; however, processors are required to provide a mode of operation in which such expressions are accepted, thus retaining backwards compatibility.

In expressions that deliver a function item, notably partial function applications, named function references, and the fn:function-lookup function, errors may now be detected at the point where the function item is created when they were previously detected at the point where the function item was called. This was underspecified in previous versions. For example, the partial function application contains(?, 42) is now required to raise a type error (because the second argument should be a string, not an integer) at the point where the partial function application occurs, not at the point where the resulting function is called.

As explained in 3.4.3 Function Coercion, the fact that coercion rules are now applied to global variables and local variable bindings introduces an incompatibility in the case of variables whose value is a function item. Previously it was possible to supply a function item that accepted a wider range of argument values than those declared in the variable's type declaration; this is no longer the case.

J.2 Incompatibilities relative to XQuery 3.0

The following names are now reserved, and cannot appear as function names (see A.4 Reserved Function Names):

  • map

  • array

J.3 Incompatibilities relative to XQuery 1.0

The following names are now reserved, and cannot appear as function names (see A.4 Reserved Function Names):

  • function

  • namespace-node

  • switch

If U is a union type with T as one of its members, and if E is an element with T as its type annotation, the expression E instance of element(*, U) returns true in both XQuery 3.0 and 3.1. In XQuery 1.0, it returns false.

Note:

This is not an incompatibility with XQuery 3.0. It should be included in XQuery 3.0 as an incompatibility with XQuery 1.0, but it was discovered after publication.

K Change Log (Non-Normative)

  1. Use the arrows to browse significant changes since the 3.1 version of this specification.

    See 1 Introduction

  2. Sections with significant changes are marked Δ in the table of contents.

    See 1 Introduction

  3. Setting the default namespace for elements and types to the special value ##any causes an unprefixed element name to act as a wildcard, matching by local name regardless of namespace.

    See 3.2.7.2 Element Test

  4. The terms FunctionType, ArrayType, MapType, and RecordType replace FunctionTest, ArrayTest, MapTest, and RecordTest, with no change in meaning.

    See 3.2.8.1 Function Type

  5. Record types are added as a new kind of ItemType, constraining the value space of maps.

    See 3.2.8.3 Record Type

  6. Function coercion now allows a function with arity N to be supplied where a function of arity greater than N is expected. For example this allows the function true#0 to be supplied where a predicate function is required.

    See 3.4.3 Function Coercion

  7. The symbols × and ÷ can be used for multiplication and division.

    See 4.8 Arithmetic Expressions

  8. The rules for value comparisons when comparing values of different types (for example, decimal and double) have changed to be transitive. A decimal value is no longer converted to double, instead the double is converted to a decimal without loss of precision. This may affect compatibility in edge cases involving comparison of values that are numerically very close.

    See 4.10.1 Value Comparisons

  9. Operators such as < and > can use the full-width forms and to avoid the need for XML escaping.

    See 4.10.2 General Comparisons

  10. The lookup operator ? can now be followed by a string literal, for cases where map keys are strings other than NCNames. It can also be followed by a variable reference.

    See 4.14.3 Lookup Expressions

  11. The arrow operator => is now complemented by a “mapping arrow” operator =!> which applies the supplied function to each item in the input sequence independently.

    See 4.23.2 Mapping Arrow Expressions

  12. All implementations must now predeclare the namespace prefixes math, map, array, and err. In XQuery 3.1 it was permitted but not required to predeclare these namespaces.

    See 5.13 Namespace Declaration

  13. Function definitions in the static context may now have optional parameters, provided this does not cause ambiguity across multiple function definitions with the same name. Optional parameters are given a default value, which can be any expression, including one that depends on the context of the caller (so an argument can default to the context value).

    See 5.18 Function Declarations

  14. The operator mapping table has been simplified by removing entries for the operators ne, le, gt, and ge; these are now defined by reference to the rules for the operators eq and lt.

    See B.2 Operator Mapping

  15. $err:map contains entries for all values that are bound to the single variables.

    See 4.20 Try/Catch Expressions

  16. $err:stack-trace provides information about the current state of execution.

    See 4.20 Try/Catch Expressions

  17. PR 1023 1128 

    It has been clarified that function coercion applies even when the supplied function item matches the required function type. This is to ensure that arguments supplied when calling the function are checked against the signature of the required function type, which might be stricter than the signature of the supplied function item.

    See 3.4.3 Function Coercion

  18. PR tba 

    Predicates in filter expressions for maps and arrays can now be numeric.

    See 4.14.4 Filter Expressions for Maps and Arrays

  19. The ordered { E } and unordered { E } expressions are retained for backwards compatibility reasons, but in XQuery 4.0 they are deprecated and have no useful effect.

    See 4.15 Ordered and Unordered Expressions

    The ordering mode declaration is retained for backwards compatibility reasons, but in XQuery 4.0 it is deprecated and has no useful effect.

    See 5.7 Ordering Mode Declaration

  20. The static typing feature has been dropped.

    See 6 Conformance

    Parts of the static context that were there purely to assist in static typing, such as the statically known documents, were no longer referenced and have therefore been dropped.

    See C.1 Static Context Components

  21. The syntax record() is allowed; the only thing it matches is an empty map.

    See 3.2.8.3 Record Type

  22. The context value static type, which was there purely to assist in static typing, has been dropped.

    See 2.2.1 Static Context

  23. Four new axes have been defined: preceding-or-self, preceding-sibling-or-self, following-or-self, and following-sibling-or-self.

    See 4.6.4.1 Axes

  24. The syntax document-node(N), where N is a NameTestUnion, is introduced as an abbreviation for document-node(element(N)). For example, document-node(*) matches any well-formed XML document (as distinct from a document fragment).

    See 3.2.7 Node Types

  25. PR 159 

    Keyword arguments are allowed on static function calls, as well as positional arguments.

    See 4.5.1.1 Static Function Call Syntax

  26. PR 202 

    The presentation of the rules for the subtype relationship between sequence types and item types has been substantially rewritten to improve clarity; no change to the semantics is intended.

    See 3.3 Subtype Relationships

  27. PR 230 

    The rules for “errors and optimization” have been tightened up to disallow many cases of optimizations that alter error behavior. In particular there are restrictions on reordering the operands of and and or, and of predicates in filter expressions, in a way that might allow the processor to raise dynamic errors that the author intended to prevent.

    See 2.4.5 Guarded Expressions

  28. PR 254 

    The term "function conversion rules" used in 3.1 has been replaced by the term "coercion rules".

    See 3.4 Coercion Rules

    The coercion rules allow “relabeling” of a supplied atomic item where the required type is a derived atomic type: for example, it is now permitted to supply the value 3 when calling a function that expects an instance of xs:positiveInteger.

    See 3.4 Coercion Rules

    The value bound to a variable in a let clause is now converted to the declared type by applying the coercion rules.

    See 4.13.3 Let Clause

    The coercion rules are now used when binding values to variables (both global variable declarations and local variable bindings). This aligns XQuery with XSLT, and means that the rules for binding to variables are the same as the rules for binding to function parameters.

    See 5.16 Variable Declaration

  29. PR 284 

    Alternative syntax for conditional expressions is available: if (condition) { X } else { Y }, with the else part being optional.

    See 4.16 Conditional Expressions

  30. PR 286 

    Element and attribute tests can include alternative names: element(chapter|section), attribute(role|class).

    See 3.2.7 Node Types

    The NodeTest in an AxisStep now allows alternatives: ancestor::(section|appendix)

    See 3.2.7 Node Types

    Element and attribute tests of the form element(N) and attribute(N) now allow N to be any NameTest, including a wildcard. The forms element(A|B) and attribute(A|B) are also allowed.

    See 3.2.7.2 Element Test

    See 3.2.7.4 Attribute Test

  31. PR 324 

    String templates provide a new way of constructing strings: for example `{$greeting}, {$planet}!` is equivalent to $greeting || ', ' || $planet || '!'

    See 4.9.2 String Templates

  32. PR 326 

    Support for higher-order functions is now a mandatory feature (in 3.1 it was optional).

    See 6 Conformance

  33. PR 344 

    A for member clause is added to FLWOR expressions to allow iteration over an array.

    See 4.13.2 For Clause

  34. PR 364 

    Switch expressions now allow a case clause to match multiple atomic items.

    See 4.18 Switch Expressions

  35. PR 368 

    The concept of the context item has been generalized, so it is now a context value. That is, it is no longer constrained to be a single item.

    See 2.2.2 Dynamic Context

    See 5.17 Context Value Declaration

  36. PR 433 

    Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability.

    See 4.2.1.1 Numeric Literals

  37. PR 483 

    The start clause in window expressions has become optional, as well as the when keyword and its associated expression.

    See 4.13.4 Window Clause

  38. PR 493 

    A new variable err:map is available, capturing all error information in one place.

    See 4.20 Try/Catch Expressions

  39. PR 519 

    The rules for tokenization have been largely rewritten. In some cases the revised specification may affect edge cases that were handled in different ways by different 3.1 processors, which could lead to incompatible behavior.

    See A.3 Lexical structure

  40. PR 521 

    New abbreviated syntax is introduced (focus function) for simple inline functions taking a single argument. An example is fn { ../@code }

    See 4.5.2.5 Inline Function Expressions

  41. PR 587 

    Switch and typeswitch expressions can now be written with curly brackets, to improve readability.

    See 4.18 Switch Expressions

    See 4.21.2 Typeswitch

  42. PR 603 

    The rules for reporting type errors during static analysis have been changed so that a processor has more freedom to report errors in respect of constructs that are evidently wrong, such as @price/@value, even though dynamic evaluation is defined to return an empty sequence rather than an error.

    See 2.4.6 Implausible Expressions

    See 4.6.4.3 Implausible Axis Steps

  43. PR 635 

    The rules for the consistency of schemas imported by different query modules, and for consistency between imported schemas and those used for validating input documents, have been defined with greater precision. It is now recognized that these schemas will not always be identical, and that validation with respect to different schemas may produce different outcomes, even if the components of one are a subset of the components of the other.

    See 5.11 Schema Import

  44. PR 659 

    In previous versions the interpretation of location hints in import schema declarations was entirely at the discretion of the processor. To improve interoperability, XQuery 4.0 recommends (but does not mandate) a specific strategy for interpreting these hints.

    See 5.11 Schema Import

  45. PR 678 

    The comparand expression in a switch expression can be omitted, allowing the switch cases to be provided as arbitrary boolean expressions.

    See 4.18 Switch Expressions

  46. PR 682 

    The values true() and false() are allowed in function annotations, and negated numeric literals are also allowed.

    See 5.18.4 Function Annotations

  47. PR 691 

    Enumeration types are added as a new kind of ItemType, constraining the value space of strings.

    See 3.2.6 Enumeration Types

  48. PR 728 

    The syntax record(*) is allowed; it matches any map.

    See 3.2.8.3 Record Type

  49. PR 753 

    The default namespace for elements and types can now be declared to be fixed for a query module, meaning it is unaffected by a namespace declaration appearing on a direct element constructor.

    See 4.12.1.2 Namespace Declaration Attributes

    See 5.14 Default Namespace Declaration

  50. PR 815 

    The coercion rules now allow conversion in either direction between xs:hexBinary and xs:base64Binary.

    See 3.4 Coercion Rules

  51. PR 820 

    The value bound to a variable in a for clause is now converted to the declared type by applying the coercion rules.

    See 4.13.2 For Clause

  52. PR 837 

    A deep lookup operator ?? is provided for searching trees of maps and arrays.

    See 4.14.3 Lookup Expressions

  53. PR 911 

    The coercion rules now allow any numeric type to be implicitly converted to any other, for example an xs:double is accepted where the required type is xs:double.

    See 3.4 Coercion Rules

  54. PR 943 

    A FLWOR expression may now include a while clause, which causes early exit from the iteration when a condition is encountered.

    See 4.13.6 While Clause

  55. PR 985 

    With the lookup arrow expression and the =?> operator, a function in a map can be looked up and called with the map as first argument.

    See 4.23.3 Lookup Arrow Expressions

  56. PR 996 

    The value of a predicate in a filter expression can now be a sequence of integers.

    See 4.4 Filter Expressions

  57. PR 1031 

    An otherwise operator is introduced: A otherwise B returns the value of A, unless it is an empty sequence, in which case it returns the value of B.

    See 4.17 Otherwise Expressions

  58. PR 1071 

    In map constructors, the keyword map is now optional, so map { 0: false(), 1: true() } can now be written { 0: false(), 1: true() }, provided it is used in a context where this creates no ambiguity.

    See 4.14.1.1 Map Constructors

  59. PR 1125 

    Lookup expressions can now take a modifier (such as keys, values, or pairs) enabling them to return structured results rather than a flattened sequence.

    See 4.14.3 Lookup Expressions

  60. PR 1132 

    Choice item types (an item type allowing a set of alternative item types) are introduced.

    See 3.2.5 Choice Item Types

  61. PR 1163 

    Filter expressions for maps and arrays are introduced.

    See 4.14.4 Filter Expressions for Maps and Arrays

  62. PR 1181 

    The default namespace for elements and types can be set to the value ##any, allowing unprefixed names in axis steps to match elements with a given local name in any namespace.

    See 2.2.1 Static Context

    If the default namespace for elements and types has the special value ##any, then an unprefixed name in a NameTest acts as a wildcard, matching names in any namespace or none.

    See 4.6.4.2 Node Tests

    The default namespace for elements and types can be set to the value ##any, allowing unprefixed names in axis steps to match elements with a given local name in any namespace.

    See 5.14 Default Namespace Declaration

  63. PR 1197 

    The keyword fn is allowed as a synonym for function in function types, to align with changes to inline function declarations.

    See 3.2.8.1 Function Type

    In inline function expressions, the keyword function may be abbreviated as fn.

    See 4.5.2.5 Inline Function Expressions

  64. PR 1212 

    XQuery 3.0 included empty-sequence and item as reserved function names, and XQuery 3.1 added map and array. This was unnecessary since these names never appear followed by a left parenthesis at the start of an expression. They have therefore been removed from the list. New keywords introducing item types, such as record and enum, have not been included in the list.

    See A.4 Reserved Function Names

  65. PR 1249 

    A for key/value clause is added to FLWOR expressions to allow iteration over a map.

    See 4.13.2 For Clause

  66. PR 1250 

    Several decimal format properties, including minus sign, exponent separator, percent, and per-mille, can now be rendered as arbitrary strings rather than being confined to a single character.

    See 2.2.1.2 Decimal Formats

    See 5.10 Decimal Format Declaration

  67. PR 1254 

    The rules concerning the interpretation of xsi:schemaLocation and xsi:noNamespaceSchemaLocation attributes have been tightened up.

    See 4.24 Validate Expressions

  68. PR 1265 

    The rules regarding the document-uri property of nodes returned by the fn:collection function have been relaxed.

    See 2.2.2 Dynamic Context

  69. PR 1344 

    Parts of the static context that were there purely to assist in static typing, such as the statically known documents, were no longer referenced and have therefore been dropped.

    See 2.2.1 Static Context

    The static typing option has been dropped.

    See 2.3 Processing Model

  70. PR 1361 

    The term atomic value has been replaced by atomic item.

    See 2.1.2 Values

  71. PR 1384 

    If a type declaration is present, the supplied values in the input sequence are now coerced to the required type. Type declarations are now permitted in XPath as well as XQuery.

    See 4.19 Quantified Expressions

  72. PR 1432 

    In earlier versions, the static context for the initializing expression excluded the variable being declared. This restriction has been lifted.

    See 5.16 Variable Declaration

  73. PR 1480 

    When the element name matches a language keyword such as div or value, it must now be written in quotes as a string literal. This is a backwards incompatible change.

    See 4.12.3.1 Computed Element Constructors

    When the attribute name matches a language keyword such as by or of, it must now be written in quotes as a string literal. This is a backwards incompatible change.

    See 4.12.3.2 Computed Attribute Constructors

  74. PR 1498 

    The EBNF operators ++ and ** have been introduced, for more concise representation of sequences using a character such as "," as a separator. The notation is borrowed from Invisible XML.

    See 2.1 Terminology

    The EBNF notation has been extended to allow the constructs (A ++ ",") (one or more occurrences of A, comma-separated, and (A ** ",") (zero or more occurrences of A, comma-separated.

    See 2.1.1 Grammar Notation

    The EBNF operators ++ and ** have been introduced, for more concise representation of sequences using a character such as "," as a separator. The notation is borrowed from Invisible XML.

    See A.1 EBNF

    See A.1.1 Notation

  75. PR 1513 

    When the processing instruction name matches a language keyword such as try or validate, it must now be written in quotes as a string literal. This is a backwards incompatible change.

    See 4.12.3.5 Computed Processing Instruction Constructors

    When the namespace prefix matches a language keyword such as as or at, it must now be written in quotes as a string literal. This is a backwards incompatible change.

    See 4.12.3.7 Computed Namespace Constructors