W3C

XQuery 4.0 and XPath 4.0 WG Review Draft

W3C Editor's Draft 30 January 2024

This version:
http://www.w3.org/TR/2000/WD-shared-40-20000101/
Most recent version of XQuery and XPath:
http://www.w3.org/TR/shared/
Most recent Recommendation of XQuery and XPath:
https://www.w3.org/TR/2017/REC-xpath-31-20170321/ 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

XQuery 4.0 and XPath 4.0 is an expression language that allows the processing of values conforming to the data model defined in [XQuery and XPath Data Model (XDM) 3.1]. The name of the language derives from its most distinctive feature, the path expression, which provides a means of hierarchic addressing of the nodes in an XML tree. As well as modeling the tree structure of XML, the data model also includes atomic values, function items, maps, arrays, and sequences. This version of XPath supports JSON as well as XML, and adds many new functions in [XQuery and XPath Functions and Operators 4.0].

XQuery 4.0 and XPath 4.0 is a superset of [XML Path Language (XPath) Version 3.0]. A detailed list of changes made since XPath 3.0 can be found in L Change Log.

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.

JSON is a lightweight data-interchange format that is widely used to exchange data on the web and to store data in databases. Many applications use JSON together with XML and HTML. XQuery 4.0 and XPath 4.0 extends XQuery to support JSON as well as XML, adding maps and arrays to the data model and supporting them with new expressions in the language and new functions in [XQuery and XPath Functions and Operators 4.0]. A list of changes made since XQuery 3.1 can be found in L Change Log. These are the most important new features in XQuery 4.0 and XPath 4.0:

  1. 4.16.1 Maps.

  2. 4.16.2 Arrays.

Status of this Document

This is a first proposal by the editor, with no official standing whatsoever. Comments are invited.


1 Introduction

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 meet the requirements identified by the W3C XML Query Working Group [XQuery 3.1 Requirements]. It 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 XML information sources, including both databases and documents. The Query Working Group has identified a requirement for both a non-XML query syntax and an XML-based query syntax. XQuery is designed to meet the first of these requirements. XQuery is 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].

The primary purpose of XPath is to address the nodes of XML trees and JSON trees. XPath gets its name from its use of a path notation for navigating through the hierarchical structure of an XML document. XPath uses a compact, non-XML syntax, allowing XPath expressions to be embedded within URIs and to be used as XML attribute values. XQuery 4.0 and XPath 4.0 adds a similar syntax for navigating JSON trees.

[Definition: XQuery 4.0 and XPath 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) 3.1].]

XPath is designed to be embedded in a host language such as [XSL Transformations (XSLT) Version 3.0] or [XQuery 3.1: An XML Query Language]. [Definition: A host language for XPath is a language or specification that incorporates XPath as a sublanguage and that defines how the static and dynamic context for evaluation of XPath expressions are to be established.]

XQuery 4.0 is an extension of XPath 4.0. XPath 4.0 is a subset of XQuery 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, and their editors jointly work together.

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

[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 and XPath 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 expressions. 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 and XPath 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:

[180]    FunctionCall    ::=    EQName ArgumentList /* xgc: reserved-function-names */
/* gn: parens */
[159]    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 and XPath 4.0. In this document, examples and material labeled as “Note” are provided for explanatory purposes and are not normative.

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

A language aspect described in this specification as implementation-defined or implementation dependent may be further constrained by the specifications of a host language in which XPath is embedded.

2 Basics

2.1 Terminology

The basic building block of XQuery 4.0 and XPath 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 and XPath 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 and XPath 4.0 is a case-sensitive language. Keywords in XQuery 4.0 and XPath 4.0 use lower-case characters and are not reserved—that is, names in XQuery 4.0 and XPath 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.

2.1.1 Values

[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 value, a node, or a function item.]

[Definition: An atomic value 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 6 Nodes DM31.] 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 values. 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 4.16.1 Maps) and arrays (see 4.16.2 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.

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. As of XPath 2.0, the namespace axis is deprecated and need not be supported by a host language. A host language that does not support the namespace axis need not represent namespace bindings in the form of nodes.

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 [XML Path Language (XPath) Version 3.1]. 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 3.1] 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)}

2.1.2 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 Collations FO31), and the namespace URI parts must either both be absent, or must be equal under the Unicode codepoint collation.

In the XQuery 4.0 and XPath 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.

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

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

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

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

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

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

This document also uses the namespace URI http://www.w3.org/2012/xquery for which no prefix is used in this document, which is reserved for use in this specification. It is currently used for annotations and option declarations that are defined by the XML Query Working Group.

[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 Literals and 4.13.1.2 Namespace Declaration Attributes for details.

2.2 Module Context and Expression Context

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

[Definition: The module context for a given module consists of all the information that is accessible to top-level expressions in the module.] The context of a top-level expression is defined based on the context of the module in which it is defined: the context of the QueryBody is the context of the main module, and the context for evaluating a function body or for a variable’s initializing expression is defined based on the context of the module in which the function or variable is defined.

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

2.2.1 Static Context

[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. A default initial value for each component must be specified by the host language. The scope of each component is specified in D.1 Static Context Components. Rules governing the initialization and alteration of these components can be found in C.1 Static Context Components.

  • [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. This value is true if rules for backward compatibility with XPath Version 1.0 are in effect; otherwise it is 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 a namespace URI, or absentDM31. 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.

    • If the value is absentDM31, 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 absentDM31. 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: Context value static type. This is a sequence type; it defines the static type of the context value within the scope of a given expression.]

  • [Definition: Item type aliases. This is a mapping from expanded QName to ItemTypes.]

    [Definition: A type alias is an expanded QName that is mapped to an ItemType in the item type aliases of the static context.]

    Item type aliases 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.

    Note:

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

    Item type aliases can be defined in a host language such as XQuery 4.0 and in XSLT 4.0, but not in XPath 4.0 itself.

  • [Definition: Statically known function definitions. This is a set of 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 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 set of implementation-defined external functions in addition to the core function library described in [XQuery and XPath Functions and Operators 4.0] or a host language.

      [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.

    • The function name, which is an expanded QName.

    • A (possibly empty) list of required parameters, each having:

    • A (possibly empty) list of optional parameters, each having:

    • A return type (a sequence type)

    • 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 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.

    System functions (also commonly called built-in functions) are function definitions that are always present in the static context by virtue of rules in the host language; they will typically include the functions specified in [XQuery and XPath Functions and Operators 4.0].

    The function definitions are available for reference from a static function call, or from a named function reference.

  • [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 strings FO31.]

  • [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: Ordering mode. Ordering mode, which has the value ordered or unordered, affects the ordering of the result sequence returned by certain expressions, as discussed in 4.18 Ordered and Unordered Expressions.]

  • [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 4.17.8 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 4.13.1.4 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 4.13.1 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. If E is a subexpression of F then the Static Base URI of E is the same as the Static Base URI of F. There are no constructs in XPath that require resolution of relative URI references during static analysis.

    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 documents. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument. ] If the argument to fn:doc is a string literal that is not present in statically known documents, then the static type of fn:doc is document-node()?.

    Note:

    The purpose of the statically known documents is to provide static type information, not to determine which documents are available. A URI need not be found in the statically known documents to be accessed using fn:doc.

  • [Definition: Statically known collections. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of items that would result from calling the fn:collection function with this URI as its argument.] If the argument to fn:collection is a string literal that is not present in statically known collections, then the static type of fn:collection is item()*.

    Note:

    The purpose of the statically known collections is to provide static type information, not to determine which collections are available. A URI need not be found in the statically known collections to be accessed using fn:collection.

  • [Definition: Statically known default collection type. This is the type of the sequence of items that would result from calling the fn:collection function with no arguments.] Unless initialized to some other value by an implementation, the value of statically known default collection type is item()*.

  • [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.]

    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.

    The following properties specify characters used both in the picture string, and in the formatted number. In each case the value is a single character:

    • [Definition: decimal-separator is the character used to separate the integer part of the number from the fractional part, both in the picture string and in the formatted number; the default value is the period character (.)]

    • [Definition: exponent-separator is the character used to separate the mantissa from the exponent in scientific notation both in the picture string and in the formatted number; the default value is the Unicode Latin small letter e character (#x65).]

    • [Definition: grouping-separator is the character typically used as a thousands separator, both in the picture string and in the formatted number; the default value is the comma character (,)]

    • [Definition: percent is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-hundred fraction; the default value is the percent character (%)]

    • [Definition: per-mille is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-thousand fraction; the default value is the Unicode per mille sign character (#x2030)]

    • [Definition: zero-digit is the character used to represent the digit zero; the default value is the Unicode digit zero (#x30). 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: 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.]

    The following properties specify characters to be used in the picture string supplied to the fn:format-number function, but not in the formatted number. In each case the value must be a single character.

    • [Definition: digit is a character used in the picture string to represent an optional digit; the default value is the number sign character (#)]

    • [Definition: pattern-separator is a character used to separate positive and negative sub-pictures in a picture string; the default value is the semicolon character (;)]

    The following properties specify characters or strings that may appear in the result of formatting the number, but not in the picture string:

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

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

    • [Definition: minus-sign is the single character used to mark negative numbers; the default value is the hyphen-minus character (#x2D). ]

2.2.2 Dynamic Context

[Definition: The dynamic context of an expression is defined as information that is needed for the dynamic evaluation of an expression.] If evaluation of an expression relies on some part of the dynamic context that is absentDM31, a dynamic error is raised [err:XPDY0002].

The individual components of the dynamic context are described below. Rules governing the initialization and alteration of these components can be found in C.2 Dynamic Context Components. Further rules governing the semantics of these components can be found in D.2 Dynamic Context Components.

The dynamic context consists of all the components of the static context, and the additional components 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. If any component in the focus is defined, both the context value and context position are known.

Note:

If any component in the focus is defined, context size is usually defined as well. However, when streaming, the context size cannot be determined without lookahead, so it may be undefined. If so, expressions like last() will raise a dynamic error because the context size is undefined.

[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 operator E1/E2, the simple map operator E1!E2, and the predicate E1[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 absentDM31, 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 an expression, 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 an expression, 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 formatting dates and times using functions such as fn:format-date and fn:format-dateTime, 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.]

  • [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 is not limited to the set of statically known documents, and it may be empty.

    If there are one or more URIs in available documents that map to a document node D, then the document-uri property of D must either be absent, or must be one of these URIs.

    Note:

    This means that given a document node $N, the result of fn:doc(fn:document-uri($N)) is $N will always be true, unless fn:document-uri($N) is an empty sequence.

  • [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 is not limited to the set of statically known documents, and it 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 is not limited to the set of statically known collections, and it may be empty.

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

    Note:

    This means that for any document node $N retrieved using the fn:collection function, either directly or by navigating to the root of a node that was returned, the result of fn:doc(fn:document-uri($N)) is $N will always be true, unless fn:document-uri($N) is an empty sequence. This implies a requirement for the fn:doc and fn:collection functions to be consistent in their effect. If the implementation uses catalogs or user-supplied URI resolvers to dereference URIs supplied to the fn:doc function, the implementation of the fn:collection function must take these mechanisms into account. For example, an implementation might achieve this by mapping the collection URI to a set of document URIs, which are then resolved using the same catalog or URI resolver that is used by the fn:doc function.

  • [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 expression is evaluated.

2.3 Processing Model

XQuery 4.0 and XPath 4.0 is defined in terms of the data model and the expression context.

Processing                          Model OverviewProcessing                          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 and XPath 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 2.3.4 Serialization). The area inside the boundaries of the language is known as the query processing domain XPath processing domain , which includes the static analysis and dynamic evaluation phases (see 2.3.3 Expression Processing). Consistency constraints on the query XPath processing domain are defined in 2.3.5 Consistency Constraints.

2.3.1 Data Model Generation

The input data for a query an expression must be represented as one or more XDM instances. This process occurs outside the domain of XQuery 4.0 and XPath 4.0, which is why Figure 1 represents it in the external processing domain. 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 Fig. 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) 3.1]. (See DM2 in Fig. 1.)

The above steps provide an example of how an XDM instance might be constructed. An XDM instance might also be synthesized directly from a relational database, or constructed in some other way (see DM3 in Fig. 1.) XQuery 4.0 and XPath 4.0 is defined in terms of the data model, but it does not place any constraints on how XDM instances are constructed.

[Definition: Each element node and attribute node in an XDM instance has a type annotation (described in Section 2.7 Schema Information DM31). The type annotation of a node is a reference to an XML Schema type. ] The type-name of a node is the name of the type referenced by its type annotation. If the XDM instance was derived from a validated XML document as described in Section 3.3 Construction from a PSVI DM31, the type annotations of the element and attribute nodes are derived from schema validation. XQuery 4.0 and XPath 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 annotation xs: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 type xs: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 2.3.5 Consistency Constraints.

The in-scope schema definitions in the static context are provided by the host language (see step SI1 in Figure 1) and must satisfy the consistency constraints defined in 2.3.5 Consistency Constraints.

2.3.3 Expression Processing

XQuery 4.0 and XPath 4.0 defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Fig. 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 XPath expression is 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 3.6.3.2 Element Test and 3.6.3.4 Attribute Test.)

The operation tree is then 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 XQuery 3.1 and XPath 3.1, 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 of type xs:double.

If the Static Typing Feature Static Typing Feature is in effect, a processor must raise a type error during static analysis if the inferred static type of an expression is not subsumed by the required type of the context where the expression is used. For example, the call of substring above would cause a type error if the inferred static type of $a is xs:integer; equally, a type error would be reported during static analysis if the inferred static type is xs:anyAtomicType.

If the Static Typing Feature Static Typing Feature is not in effect, a processor may raise a type error during static analysis only when one of the following conditions is met:

  1. When 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.

  2. When the only possible value of an expression that is consistent with the required type is the empty sequence. Consider for example the expression fn:codepoints-to-string(fn:tokenize($in)). Since fn:codepoints-to-string requires xs:integer* while fn:tokenize($in) delivers xs:string*, this expression can succeed only in the special case where the value is empty, so processors may report this as an error. An error must not be raised under this rule unless both the inferred static type and the required type permit values other than the empty sequence.

  3. When an ForwardStep or ReverseStep is used, and it is known during static analysis that the step will select no nodes.

    One example of this is an expression such as @price/text(): attribute nodes never have children, so this expression will never select anything.

    Another example arises when schema information is available: if it is known that the variable $emp holds a value of type schema-element(employee), and that no element of this type can have an attribute named @sallary (sic), then a type error may be reported if the expression $emp/@sallary is encountered.

    Note:

    A static error must not be reported simply because a predicate will always return false: the expression a[name()='b'] will always return an empty sequence, but it is not an error.

  4. When the KeySpecifier in a Lookup expression is such that the result of the lookup will inevitably be empty. For example if the context value is known to be of type record(longitude, latitude) then a static type error may be raised against the expression ?altitude.

For backwards compatibility, processors should provide an option to avoid reporting type errors in respect of constructs such as @a/@b that were executed without error in previous versions. Note in particular that the construct /.. was sometimes recommended in XPath 1.0 as the preferred way to denote an empty node-set.

Alternatively, if the Static Typing Feature Static Typing Feature is not in effect, 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. If the Static Typing Feature Static Typing Feature is in effect, all type errors are detected during static analysis and serve to inhibit the dynamic evaluation 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 type T 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 value 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 value 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.

When the Static Typing Feature Static Typing Feature is in effect, it is also possible for static analysis of an expression to raise a type error, even though execution of the expression on certain inputs would be successful. For example, an expression might contain a function that requires an element as its parameter, and the static analysis phase might infer the static type of the function parameter to be an optional element. This case is treated as a type error and inhibits evaluation, even though the function call would have been successful for input data in which the optional element is present.

2.3.4 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 3.1].]

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 3.1] is outside the scope of the XQuery 4.0 and XPath 4.0 specification.

The host language may provide a serialization option.

Note:

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

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.

[XSLT and XQuery Serialization 3.1] 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 C.1 Static Context Components. 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 Parameters SER31. 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/me/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 Data Model Instance SER31. 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.

2.3.5 Consistency Constraints

In order for XQuery 4.0 and XPath 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 and XPath 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 an expression 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 equivalent to its definition in the type annotation.

  • 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 mapping of a string to a document node in available documents, if there exists a mapping of the same string to a document type in statically known documents, the document node must match the document type, using the matching rules in 3.5 Sequence Type Matching.

  • For each mapping of a string to a sequence of items in available collections, if there exists a mapping of the same string to a type in statically known collections, the sequence of items must match the type, using the matching rules in 3.5 Sequence Type Matching.

  • The sequence of items in the default collection must match the statically known default collection type, using the matching rules in 3.5 Sequence Type Matching.

  • The context value must match the context value static type, using the matching rules in 3.5 Sequence Type Matching.

  • 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 3.5 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 3.5 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 3.5 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. If two participating ISSDs contain a definition for the same schema type, element name, or attribute name, the definitions must be equivalent in both ISSDs. In this context, equivalence means that validating an instance against type T in one ISSD will always have the same effect as validating the same instance against type T in the other ISSD (that is, it will produce the same PSVI, insofar as the PSVI is used during subsequent processing). This means, for example, that the membership of the substitution group of an element declaration in one ISSD must be the same as that of the corresponding element declaration in the other ISSD; that the set of types derived by extension from a given type must be the same; and that in the presence of a strict or lax wildcard, the set of global element (or attribute) declarations capable of matching the wildcard must be the same.

  • 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 and XPath 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.

During the static analysis phase, if the Static Typing Feature Static Typing Feature is in effect and the static type assigned to an expression other than () or data(()) is empty-sequence(), a static error is raised [err:XPST0005]. This catches cases in which a query refers to an element or attribute that is not present in the in-scope schema definitions, possibly because of a spelling error.

Independently of whether the Static Typing Feature Static Typing Feature is in effect, if an implementation can determine during the static analysis phase that a QueryBody an XPath expression, 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 an XPath expression statically only if the query expression 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 and XPath 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:XPYYnnnn 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.

  • XP identifies the error as an XPath error (some errors, originally defined by XQuery and later added to XPath, use the code XQ instead).

  • 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 XPath to another. However, the contents of this namespace may be extended to include additional error definitions.

The method by which an XQuery 4.0 and XPath 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 3.17 Try/Catch Expressions XQ31. The host language may also provide error handling mechanisms.

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:error FO31. 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

[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 for expression (ForExpr) such as for $x in S return E, the expression E is guarded by the existence of an item bound to $x.

    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

[Definition: Certain expressions, while not erroneous, are classified as being implausible, because there is a high probability that they were written incorrectly.]

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.

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 and XPath 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.

2.5 Concepts

This section explains some concepts that are important to the processing of XQuery 4.0 and XPath 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 expression, which may consist of one or more trees (documents or fragments). Document order is defined in Section 2.4 Document Order DM31, 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 expression, 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. Namespace nodes immediately follow the element node with which they are associated. The relative order of namespace nodes is stable but implementation-dependent.

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

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

  6. 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 Atomization

The semantics of some XQuery 4.0 and XPath 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 values is required. The result of atomization is either a sequence of atomic values or a type error [err:FOTY0012]FO31. [Definition: Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.4 fn:data FO31.]

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

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

  • If the item is a node, its typed value is returned (a type error [err:FOTY0012]FO31 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]FO31 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

2.5.3 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:boolean FO31.]

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]FO31.

    Note:

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

Note:

The effective boolean value of a sequence that contains at least one node and at least one atomic value is implementation-dependent in regions of a query where ordering mode is unordered.

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.

2.5.4 Input Sources

XQuery 4.0 and XPath 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 14.6 Functions giving access to external information FO31.

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.

2.5.5 URI Literals

XQuery 4.0 and XPath 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

The type system of XQuery 4.0 and XPath 4.0 is based on [XML Schema 1.0] or [XML Schema 1.1].

[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 and XPath 4.0 expression. The term sequence type suggests that this syntax is used to describe the type of an XQuery 4.0 and XPath 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.] With the exception of the generic types item(), which matches all items, and xs:error, which matches no items, the set of items matched by an item type consists either exclusively of atomic values, exclusively of nodes, or exclusively of function itemsDM31.

Note:

These definitions require a caveat: types defined in a schema may be anonymous, in which case they cannot be referenced directly using the ItemType or SequenceType syntax. For example an element that is validated against an anonymous complex type A conforms to an item type which could be written element(*, A) but for the fact that A is anonymous.

[Definition: A schema type is a type that is (or could be) defined using the facilities of [XML Schema 1.0] or [XML Schema 1.1] (including the built-in types).] A schema type can be used as a type annotation on an element or attribute node (unless it is a non-instantiable type such as xs:NOTATION or xs:anyAtomicType, in which case its derived types can be so used). 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.)

Note:

Local union types (see 3.6.2.1 Local Union Types) and enumeration types (see 3.6.2.2 Enumeration Types) are classified as schema types, even though they are not defined in any XSD schema.

[Definition: A generalized atomic type is a schema type that is either (a) an atomic type or (b) a pure union type ].

[Definition: A pure union type is a simple type that satisfies the following constraints: (1) {variety} is union, (2) the {facets} property is empty, (3) no type in the transitive membership of the union type has {variety} list, and (4) 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 value 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:

A local union type (see 3.6.2.1 Local Union Types) is always a pure union type

Generalized atomic types represent the intersection between the categories of sequence type and schema type. A generalized atomic type, such as xs:integer or my:hatsize, is both a sequence type and a schema type.

3.1 Predefined Schema Types

The in-scope schema types in the static context are initialized with a set of predefined schema types that is determined by the host language. This set may include some or all of the schema types in the namespace http://www.w3.org/2001/XMLSchema, represented in this document by the 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) 3.1]. An implementation that has based its type system on [XML Schema 1.0] is not required to support the xs:dateTimeStamp or xs:error types.

The schema types defined in Section 2.7.2 Predefined Types DM31 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) 3.1]. 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) 3.1] 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 annotation xs: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 values (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 3.4 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 and XPath 4.0 type hierarchy can be found in Section 1.6 Type System FO31.

Type Hierarchy Diagram

Figure 2: Hierarchy of Schema Types used in XQuery 4.0 and XPath 4.0.

3.2 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 and XPath 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]FO31 if the namespace bindings for the result cannot be determined.

3.3 Typed Value and String Value

Every node has a typed value and a string value, except for nodes whose value is absentDM31. [Definition: The typed value of a node is a sequence of atomic values and can be extracted by applying the Section 2.4 fn:data FO31 function to the node.] [Definition: The string value of a node is a string and can be extracted by applying the Section 2.3 fn:string FO31 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. If the node was created by mapping from an Infoset or PSVI, the relationships among these properties are defined by rules in Section 2.7 Schema Information DM31.

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

As a convenience to the reader, 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, namespace, 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 annotation xs: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 values ("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 type hatsize, 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 absentDM31. The fn:data function raises a type error [err:FOTY0012]FO31 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 absentDM31, and the fn:data function applied to E6 raises an error.

3.4 Sequence Types

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

[230]    SequenceType    ::=    ("empty-sequence" "(" ")")
| (ItemType OccurrenceIndicator?)
[232]    ItemType    ::=    AnyItemTest | TypeName | KindTest | FunctionTest | MapTest | ArrayTest | AtomicOrUnionType | RecordTest | LocalUnionType | EnumerationType | ParenthesizedItemType
[231]    OccurrenceIndicator    ::=    "?" | "*" | "+" /* xgc: occurrence-indicators */

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 occurrence-indicators constraint.

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

  • (function(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

3.5 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 and XPath 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 and XPath 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.

3.6 Item Types

[232]    ItemType    ::=    AnyItemTest | TypeName | KindTest | FunctionTest | MapTest | ArrayTest | AtomicOrUnionType | RecordTest | LocalUnionType | EnumerationType | ParenthesizedItemType
[233]    AnyItemTest    ::=    "item" "(" ")"
[251]    TypeName    ::=    EQName
[235]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
[237]    DocumentTest    ::=    "document-node" "(" (ElementTest | SchemaElementTest)? ")"
[245]    ElementTest    ::=    "element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
[246]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[247]    ElementDeclaration    ::=    ElementName
[242]    AttributeTest    ::=    "attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
[243]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[244]    AttributeDeclaration    ::=    AttributeName
[249]    ElementName    ::=    EQName
[248]    AttributeName    ::=    EQName
[241]    PITest    ::=    "processing-instruction" "(" (NCName | StringLiteral)? ")"
[239]    CommentTest    ::=    "comment" "(" ")"
[240]    NamespaceNodeTest    ::=    "namespace-node" "(" ")"
[238]    TextTest    ::=    "text" "(" ")"
[236]    AnyKindTest    ::=    "node" "(" ")"
[252]    FunctionTest    ::=    Annotation* (AnyFunctionTest
| TypedFunctionTest)
[253]    AnyFunctionTest    ::=    "function" "(" "*" ")"
[254]    TypedFunctionTest    ::=    "function" "(" (SequenceType ("," SequenceType)*)? ")" "as" SequenceType
[270]    ParenthesizedItemType    ::=    "(" ItemType ")"
[255]    MapTest    ::=    AnyMapTest | TypedMapTest
[258]    RecordTest    ::=    AnyRecordTest | TypedRecordTest
[267]    ArrayTest    ::=    AnyArrayTest | TypedArrayTest
[234]    AtomicOrUnionType    ::=    EQName
[265]    LocalUnionType    ::=    "union" "(" ItemType ("," ItemType)* ")"
[266]    EnumerationType    ::=    "enum" "(" StringLiteral ("," StringLiteral)* ")"

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

An item type written simply as an EQName (that is, a NamedType) 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 an entry in the item type aliases 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 plain union type. See 3.6.2 Atomic and Union Types for details.

    Note:

    A name in the xs namespace will always fall into this category, since the namespace is reserved.

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

3.6.1 General item types

  • item() matches any single item.

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

  • A ParenthesizedItemType matches an item if and only if the item matches the ItemType that is in parentheses.

    Note:

    Parenthesized item types are 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 (function() as xs:boolean)*. In this example the parentheses are needed to indicate where the occurrence indicator belongs.

3.6.2 Atomic and Union Types

A generalized atomic type may be expressed as an ItemType in any of the following ways:

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

Example: The ItemType xs: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 ItemType dress-size is a union type that allows either xs:decimal values for numeric sizes (e.g. 4, 6, 10, 12), or one of an enumerated set of xs:strings (e.g. small, medium, large). The ItemType dress-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+.

3.6.2.1 Local Union Types

A LocalUnionType defines an anonymous union type locally (for example, within a function signature) which may be more convenient than defining the type in an imported schema.

[265]    LocalUnionType    ::=    "union" "(" ItemType ("," ItemType)* ")"

Although the grammar allows any ItemType to appear, each ItemType must identify a generalized atomic type [err:XPST0147].

A LocalUnionType is a generalized atomic type. It is classified as a schema type even though it is not defined in any XSD schema.

An item matches a LocalUnionType if it matches any of the generalized atomic types listed within the parentheses.

For example, the type union(xs:date, xs:dateTime, xs:time) matches any value that is an instance of xs:date, xs:dateTime, or xs:time.

Similarly, the type union(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.

Note:

Local union types are particularly useful in function signatures, allowing a function to take arguments of a variety of types. 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 union(xs:date, xs:dateTime) allows the attribute @when to be either a date, or a 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 union(xs:string, xs:anyURI, xs:untypedAtomic) returns true if $x is an instance of any of these three atomic types.

3.6.2.2 Enumeration Types

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

[266]    EnumerationType    ::=    "enum" "(" StringLiteral ("," StringLiteral)* ")"

An EnumerationType 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 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 union(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 3.7.2 Subtypes of Item Types.

An enumeration type is thus a generalized atomic type.

It follows from these rules that an atomic value 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.

3.6.3 Node Types

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 type alias.

3.6.3.1 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 ) matches any document node that contains exactly one element node, optionally accompanied by one or more comment and processing instruction nodes, if E is an ElementTest or SchemaElementTest that matches the element node (see 3.6.3.2 Element Test and 3.6.3.3 Schema Element Test).

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

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

3.6.3.2 Element Test
[245]    ElementTest    ::=    "element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
[111]    NameTestUnion    ::=    NameTest ("|" NameTest)*
[154]    NameTest    ::=    EQName | Wildcard
[155]    Wildcard    ::=    "*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
[251]    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.

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]

Note:

Substitution groups do not affect the semantics of ElementTest.

An ElementTest ET 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 NameTest NT 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.

3.6.3.3 Schema Element Test
[246]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[247]    ElementDeclaration    ::=    ElementName
[249]    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 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 SchemaElementTest schema-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.

3.6.3.4 Attribute Test
[242]    AttributeTest    ::=    "attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
[111]    NameTestUnion    ::=    NameTest ("|" NameTest)*
[154]    NameTest    ::=    EQName | Wildcard
[155]    Wildcard    ::=    "*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
[251]    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 AttributeTest AT 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 NameTest NT 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.

3.6.3.5 Schema Attribute Test
[243]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[244]    AttributeDeclaration    ::=    AttributeName
[248]    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 SchemaAttributeTest schema-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.

3.6.4 Function, Map, and Array Tests

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

The subtype relation among these types is described in the various subsections of 3.7.2 Subtypes of Item Types.

3.6.4.1 Function Test
[252]    FunctionTest    ::=    Annotation* (AnyFunctionTest
| TypedFunctionTest)
[253]    AnyFunctionTest    ::=    "function" "(" "*" ")"
[254]    TypedFunctionTest    ::=    "function" "(" (SequenceType ("," SequenceType)*)? ")" "as" SequenceType

A FunctionTest matches a function item, potentially also checking its function signatureDM31 and annotations (see 5.15 Annotations). An AnyFunctionTest matches any item that is a function. A TypedFunctionTest matches an item if it is a function and the function’s type signature (as defined in Section 2.8.1 Functions DM31) is a subtype of the TypedFunctionTest.

Here are some examples of FunctionTests:

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

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

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

  4. %assertion function(int, int) as int matches any function item with the function signature function(int, int) as int if the implementation-defined function assertion %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 FunctionTest. It uses the same syntax as 5.15 Annotations.] XQuery 4.0 and XPath 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.

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, e.g. 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 test.

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.

3.6.4.2 Map Test
[255]    MapTest    ::=    AnyMapTest | TypedMapTest
[256]    AnyMapTest    ::=    "map" "(" "*" ")"
[257]    TypedMapTest    ::=    "map" "(" ItemType "," SequenceType ")"

The MapTest map(*) matches any map. The MapTest map(X, Y) matches any map where the type of every key is an instance of X and the type of every value is an instance of Y.

Although the grammar for TypedMapTest 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 map{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()

Because of the rules for subtyping of function types according to their signature, it follows that the item type function(A) as item()*, where A is an atomic type, also matches any map, regardless of the type of the keys actually found in the map. For example, a map whose keys are all strings can be supplied where the required type is function(xs:integer) as item()*; a call on the map that treats it as a function with an integer argument will always succeed, and will always return an empty sequence.

The function signature of a map matching type map(K, V), treated as a function, is function(xs:anyAtomicType) as V?. It is thus always a subtype of function(xs:anyAtomicType) as item()* regardless of the actual types of the keys and values in the map. The rules for function coercion mean that any map can be supplied as a value in a context where the required type has a more specific return type, such as function(xs:anyAtomicType) as xs:integer, even when the map does not match in the sense required to satisfy the instance of operator. In such cases, a type error will occur only if an actual call on the map (treated as a function) returns a value that is not an instance of the required return type.

Examples:

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

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

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

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

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

  • not($M instance of function(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 function(xs:integer) as xs:string.

Rules defining whether one map type is a subtype of another are given in 3.7.2.7 Maps.

3.6.4.3 Record Test
[258]    RecordTest    ::=    AnyRecordTest | TypedRecordTest
[259]    AnyRecordTest    ::=    "record" "(" "*" ")"
[260]    TypedRecordTest    ::=    "record" "(" FieldDeclaration ("," FieldDeclaration)* ExtensibleFlag? ")"
[261]    FieldDeclaration    ::=    FieldName "?"? ("as" (SequenceType | SelfReference))?
[262]    FieldName    ::=    NCName | StringLiteral
[263]    SelfReference    ::=    ".." OccurrenceIndicator?
[264]    ExtensibleFlag    ::=    "," "*"

A RecordTest matches maps that meet specific criteria.

For example, the RecordTest record(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 test is said to be extensible. For example, the RecordTest record(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(*) define an extensible record type that has no explicit field declarations. The item type denoted by record(*) is equivalent to the item type map(*): that is, it allows any map.

A record test can constrain only those entries whose keys are strings, but when the record test is marked as extensible, then other entries may be present in the map with 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 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 RecordTest record(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 test, 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.

If a field is declared using .. (optionally followed by an occurrence indicator) in place of a SequenceType, this indicates that the record type is recursive: the value of this field, if present, must be an instance of the record type being declared. For example, a record designed to hold error information might be declared as:

record(error-code as xs:QName, message as xs:string, cause? as ..)

A map conforms to this type if it has entries with keys error-code and message of the correct types, and if the cause entry is either absent, or is a map that itself conforms to this type.

A FieldDeclaration that a SelfReference to identify its type must either be optional (marked with a question mark after the name), or must allow the empty sequence as a permitted value (marked by using the occurrence indicator ? or * after the item type). If the field is not optional and does not allow an empty sequence, a static error is raised [err:XPST0140]. This rule ensures that finite instances of the type can be constructed.

A record used to represent a node in a binary tree might be represented as:

record(left? as .., value, right? as ..)

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

declare item-type binary-tree as
    record(left? as .., value, right? as ..);                 
declare function flatten($tree as binary-tree?) as item()* {
    $tree ! (flatten(?left), ?value, flatten(?right))   
}

 

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

record(value, children as ..*)

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

declare item-type tree as
    record(value, children as ..*);                 
declare function flatten($tree as tree) as item()* {
    $tree?value, $tree?children ! flatten(.))   
}

Note:

If a RecordTest contains a SelfReference field that is not optional, and whose type does not permit an empty sequence, then it will not be possible to construct an instance. So a RecordTest such as record(a as ..) serves no practical purpose; but it is not disallowed.

Record tests 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.

In particular, 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 4.16.3.3 Implausible Lookup Expressions), and (b) the processor can make static type inferences about the type of value returned by $rec?field.

Note:

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 tests 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 function(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 test 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 tests 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 tests 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 3.7.2.9 Record Tests.

3.6.4.4 Array Test
[267]    ArrayTest    ::=    AnyArrayTest | TypedArrayTest
[268]    AnyArrayTest    ::=    "array" "(" "*" ")"
[269]    TypedArrayTest    ::=    "array" "(" SequenceType ")"

The AnyArrayTest array(*) matches any array. The TypedArrayTest array(X) matches any array in which every array member matches the SequenceType X.

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 ItemTypes, including:

  • item()

  • function(*)

  • function(xs:integer) as item()*

The function signature of an array matching array(X), treated as a function, is function(xs:integer) as X. It is thus always a subtype of function(xs:integer) as item()* regardless of the actual member types in the array. The rules for function coercion mean that any array can be supplied as a value in a context where the required type has a more specific return type, such as function(xs:integer) as xs:integer, even when the array does not match in the sense required to satisfy the instance of operator. In such cases, a type error will occur only if an actual call on the array (treated as a function) returns a value that is not an instance of the required return type.

Rules defining whether one array type is a subtype of another are given in 3.7.2.8 Arrays.

3.6.5 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 and XPath 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]FO31, regardless of the value of $x.

  • $x cast as xs:error? raises a dynamic error [err:FORG0001]FO31 if exists($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.

3.7 Subtype Relationships

[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 3.7.1 Subtypes of Sequence Types. The rules for deciding whether one item type is a subtype of another are given in 3.7.2 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.

3.7.1 Subtypes of Sequence Types

We use the notation A ⊑ B, or subtype(A, B) to indicate that a sequence type A 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 3.7.2 Subtypes of Item Types.

Sequence type B
empty Bi? Bi* Bi Bi+ void
Sequence type A empty true true true false false false
Ai? false AiBi AiBi false false false
Ai* false false AiBi false false false
Ai false AiBi AiBi AiBi AiBi false
Ai+ false false AiBi false AiBi false
void true true true true true true

3.7.2 Subtypes of Item Types

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

Before applying these rules, any ItemType written as item-type(N) is replaced with the definition of the named item type N, recursively. The rules are written in terms of the lexical form of the two item types, but it is assumed that trivial variations are first eliminated: comments and unnecessary whitespace are removed, lexical QNames are replaced by URI-qualified names with appropriate defaults applied in the case of unprefixed names, equivalent forms such as element() and element(*) are normalized.

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

3.7.2.1 General Rules

Given item types A 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 type X 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 3.7.2.2 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 .

3.7.2.2 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 3.5 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 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:
    • union(xs:short, xs:long) ⊆ xs:integer because xs:short ⊆ xs:integer and xs:long ⊆ xs:integer.

    • union(P, Q) ⊆ union(P, Q, R) because P ⊆ union(P, Q, R) and Q ⊆ union(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") ⊆ union(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.

    Note:

    This rule applies both when A is a schema-defined union type and when it is a LocalUnionType; in addition it applies when A is an enumeration type with multiple enumerated values, which is defined to be equivalent to a union type.

3.7.2.3 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 ElementTest E, and B is document-node().

    Example:

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

  4. All the following are true:

    1. A is document-node(Ae)

    2. B is document-node(Be)

    3. AeBe

    Example:

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

3.7.2.4 Node Types: Element Tests

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

More specifically, this is the case if for every NameTest M in MU there is a NameTest N 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. An wildcard-matches Bn

    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. An wildcard-matches Bn

    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. An wildcard-matches Bn

    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.

3.7.2.5 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. An wildcard-matches Bn

    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. An wildcard-matches Bn

    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

3.7.2.6 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 FunctionTest 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.

3.7.2.7 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. Both the following are true:

    1. A is map(K, V)

    2. B is function(xs:anyAtomicType) as W , where W has the same item type as V, but also allows an empty sequence.

    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.

3.7.2.8 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

3.7.2.9 Record Tests

Given item types A and B, A B 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 test.

    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 test

    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 test.

    2. B is a non-extensible record test.

    3. Every field in A is also declared in B.

    4. Every mandatory field in B is also declared 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 test

    2. B is an extensible record test

    3. Every mandatory field in B is also declared 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 test.

    2. B is an extensible record test.

    3. Every mandatory field in B is also declared in A.

    4. Every field that is declared in B with a type other than item()* is also declared 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(y as xs:integer) ⊆ record(x?, y as xs:decimal, *)

3.7.3 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 FunctionTests. 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 FunctionTests without the %local:nondeterministic annotation only match deterministic functions, subtype-assertions() must be false.

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 and XPath 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 and XPath 4.0 Grammar].

The highest-level symbol in the XPath grammar is XPath. [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.

[1]    XPath    ::=    Expr
[46]    Expr    ::=    ExprSingle ("," ExprSingle)*
[47]    ExprSingle    ::=    WithExpr
| ForExpr
| LetExpr
| FLWORExpr
| QuantifiedExpr
| SwitchExpr
| TypeswitchExpr
| IfExpr
| TryCatchExpr
| OrExpr

The XQuery 4.0 and XPath 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 an 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, ForExpr, LetExpr, QuantifiedExpr, SwitchExpr, TypeswitchExpr, IfExpr, TryCatchExpr, and OrExpr. Each of these expressions is described in a separate section of this document.

4.1 Setting Namespace Context

[48]    WithExpr    ::=    "with" NamespaceDeclaration ("," NamespaceDeclaration)* EnclosedExpr
[49]    NamespaceDeclaration    ::=    QName "=" URILiteral StringLiteral
[271]    URILiteral    ::=    StringLiteral
[42]    EnclosedExpr    ::=    "{" Expr? "}"

The namespace context for an expression can be set using a construct of the form:

with xmlns="http://example.com/,
     xmlns:a="http://example.com/a" {
       /doc/a:element/b
}

The static context for the enclosed expression will be the same as the static context for the WithExpr itself, except for modifications defined below.

The QName used in a NamespaceDeclaration must be either xmlns or xmlns:prefix where prefix is some NCName.

If more than one NamespaceDeclaration specifies the same QName, all but the last of the duplicates are ignored.

If the QName is "xmlns" then:

  • If the URILiteral StringLiteral is a zero-length string:

  • If the URILiteral StringLiteral is not zero-length:

If the QName is in the form xmlns:prefix then the URILiteral StringLiteral must not be zero-length; the effect is that a binding that maps the given prefix to the specified namespace URI is added to the statically known namespaces.

For example, the expression:

with xmlns="http://www.acme.com/" {a/b[c=3]}

is equivalent to the expression:

Q{http://www.acme.com/}a/Q{http://www.acme.com/}b[Q{http://www.acme.com/}c=3]

4.2 Comments

[287]    Comment    ::=    "(:" (CommentContents | Comment)* ":)" /* ws: explicit */
/* gn: comments */
[300]    CommentContents    ::=    (Char+ - (Char* ('(:' | ':)') Char*))

Comments may be used to provide information relevant to programmers who read a query, either in the Prolog or in the Query Body an expression. Comments are lexical constructs only, and do not affect query expression 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 :)

4.3 Primary Expressions

[Definition: Primary expressions are the basic primitives of the language. They include literals, variable references, context value expressions, 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 4.13 Node Constructors.Map and Array Constructors are described in 4.16 Maps and Arrays. String Constructors are described in 4.10.3 String Constructors.

[171]    PrimaryExpr    ::=    Literal
| VarRef
| ParenthesizedExpr
| ContextValueExpr
| FunctionCall
| OrderedExpr
| UnorderedExpr
| NodeConstructor
| FunctionItemExpr
| MapConstructor
| ArrayConstructor
| StringTemplate
| StringConstructor
| UnaryLookup
[210]    FunctionItemExpr    ::=    NamedFunctionRef | InlineFunctionExpr

4.3.1 Literals

[Definition: A literal is a direct syntactic representation of an atomic value.] XQuery 4.0 and XPath 4.0 supports two kinds of literals: numeric literals and string literals.

[172]    Literal    ::=    NumericLiteral | StringLiteral
[173]    NumericLiteral    ::=    IntegerLiteral | HexIntegerLiteral | BinaryIntegerLiteral | DecimalLiteral | DoubleLiteral
[273]    IntegerLiteral    ::=    Digits /* ws: explicit */
[274]    HexIntegerLiteral    ::=    "0x" HexDigits /* ws: explicit */
[275]    BinaryIntegerLiteral    ::=    "0b" BinaryDigits /* ws: explicit */
[276]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[277]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits /* ws: explicit */
[278]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'") /* ws: explicit */
[281]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[282]    EscapeQuot    ::=    '""' /* ws: explicit */
[283]    EscapeApos    ::=    "''" /* ws: explicit */
[294]    Digits    ::=    DecDigit ((DecDigit | "_")* DecDigit)?
[295]    DecDigit    ::=    [0-9]
[296]    HexDigits    ::=    HexDigit ((HexDigit | "_")* HexDigit)?
[297]    HexDigit    ::=    [0-9a-fA-F]
[298]    BinaryDigits    ::=    BinaryDigit ((BinaryDigit | "_")* BinaryDigit)?
[299]    BinaryDigit    ::=    [01]

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 value of type xs:integer; the value is obtained by casting from xs:string to xs:integer as specified in Section 19.2 Casting from xs:string and xs:untypedAtomic FO31.

  5. The value of a numeric literal containing . but no e or E character is an atomic value of type xs:decimal; the value is obtained by casting from xs:string to xs:decimal as specified in Section 19.2 Casting from xs:string and xs:untypedAtomic FO31.

  6. The value of a numeric literal containing an e or E character is an atomic value of type xs:double; the value is obtained by casting from xs:string to xs:double as specified in Section 19.2 Casting from xs:string and xs:untypedAtomic FO31.

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]FO31 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 values FO31 for details.)

The limits of numeric datatypes are specified in 6.4 Data Model Conformance.

The XML Schema specification allows implementations to impose a limit (which must not be less than 18 digits) on the size of integer and decimal values. The full range of values of built-in subtypes of xs:integer, such as xs:long and xs:unsignedLong, can be supported only if the limit is 20 digits or higher. Negative numbers such as the minimum value of xs:long (-9223372036854775808) are technically unary expressions rather than literals, but implementations may prefer to ensure that they are expressible.

The value of a string literal is an atomic value 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.

A string literal may contain a predefined entity reference. [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 XQuery are as follows:

Entity Reference Character Represented
&lt; <
&gt; >
&amp; &
&quot; "
&apos; '

A string literal may also contain a character reference. [Definition: A character reference is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal codepoint.] For example, the Euro symbol (€) can be represented by the character reference &#8364;. 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 literal expressions:

  • "12.5" denotes the string containing the characters 1, 2, ., and 5.

  • 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.

  • 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.

  • "He said, ""I don't like it.""" denotes a string containing two quotation marks and one apostrophe.

    Note:

    When XPath expressions are embedded in contexts where quotation marks have special significance, such as inside XML attributes, additional escaping may be needed.

    An alternative solution is to use a StringTemplate, for example `He said, "I don't like it."`. Technically this is not a literal, but a string template with no embedded expressions can be used in the same way as a string literal in nearly all contexts.

  • "Ben &amp; Jerry&apos;s" denotes the xs:string value "Ben & Jerry's".

  • "&#8364;99.50" denotes the xs:string value "€99.50".

The xs:boolean values true and false can be constructed by calls to the system functions fn: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 18.1 Constructor functions for XML Schema built-in atomic types FO31. 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 value 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 value 9 whose type is hatsize.

4.3.2 Variable References

[174]    VarRef    ::=    "$" VarName
[175]    VarName    ::=    EQName

[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.

4.3.3 Parenthesized Expressions

[176]    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 4.8.1 Sequence Concatenation.

4.3.4 Context Value Expression

[177]    ContextValueExpr    ::=    "."

A context value expression evaluates to the context value.

In many syntactic contexts, the context value will be a single item. For example this appplies on the right-hand side of the / or ! operators, or within a Predicate.

If the context value is absentDM31, a context value expression raises a dynamic error [err:XPDY0002].

Note:

Being absent is not the same thing as being empty.

4.3.5 Enclosed Expressions

[42]    EnclosedExpr    ::=    "{" Expr? "}"

[Definition: An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly braces.] [Definition: In an enclosed expression, the optional expression enclosed in curly braces 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.

4.4 Postfix Expressions

[157]    PostfixExpr    ::=    PrimaryExpr | FilterExpr | DynamicFunctionCall | LookupExpr
[156]    FilterExpr    ::=    PostfixExpr Predicate
[158]    DynamicFunctionCall    ::=    PostfixExpr PositionalArgumentList
[166]    LookupExpr    ::=    PostfixExpr Lookup

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 4.5 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 4.6.2.1 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 4.16.3.2 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.

4.5 Filter Expressions

[156]    FilterExpr    ::=    PostfixExpr Predicate
[165]    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 4.7.5 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 4.8.1 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[position() = (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.

The predicate truth value is derived by applying the following rules, in order:

  1. If the value of the predicate expression is a singleton atomic value of a numeric type or derived from a numeric type, the predicate truth value is true if the value of the predicate expression is equal (by the eq operator) to the context position, and is false otherwise. [Definition: A predicate whose predicate expression returns a numeric type is called a numeric predicate.]

    Note:

    In a region of a query where ordering mode is unordered, the result of a numeric predicate is implementation-dependent , as explained in 4.18 Ordered and Unordered Expressions.

  2. Otherwise, the predicate truth value is the effective boolean value of the predicate expression.

4.6 Functions

Functions in XQuery 4.0 and XPath 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.

4.6.1 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 4.6.1.2 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.

4.6.1.1 Static Function Call Syntax
[180]    FunctionCall    ::=    EQName ArgumentList /* xgc: reserved-function-names */
/* gn: parens */
[159]    ArgumentList    ::=    "(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
[161]    PositionalArguments    ::=    Argument ("," Argument)*
[181]    Argument    ::=    ExprSingle | ArgumentPlaceholder
[182]    ArgumentPlaceholder    ::=    "?"
[162]    KeywordArguments    ::=    KeywordArgument ("," KeywordArgument)*
[163]    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 4.6.2.3 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 4.6.1.2 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].

4.6.1.2 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 4.6.2.3 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 definition FD 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 definition FD 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 definition FD is matched to an argument expression as follows:

    1. If there are N positional arguments in the function call, 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.

  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 2.3.5 Consistency Constraints).

    • Errors raised by host-language-dependent functions are implementation-defined.

    Example: A System Function

    The following function call uses the function Section 2.5 fn:base-uri FO31. 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()

4.6.2 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 and XPath 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 4.6.2.1 Dynamic Function Calls.

A number of constructs can be used to produce a function item, notably:

  • A named function reference (see 4.6.2.4 Named Function References) constructs a function item by reference to function definitions in the static context. For example, fn:node-name#1 returns a function item whose effect is to call the static fn:node-name function with one argument.

  • An inline function (see 4.6.2.5 Inline Function Expressions ) constructs a function item whose body is defined locally. For example, the construct fn($x) { $x + 1 } returns a function item whose effect is to increment the value of the supplied argument.

  • A partial function application (see 4.6.2.3 Partial Function Application) derives one function item from another by supplying the values of some of its arguments. For example, fn:ends-with(?, ".txt") returns a function item with one argument that tests whether the supplied string ends with the substring ".txt".

  • Maps and arrays are also function items. See 4.16.1.1 Map Constructors and 4.16.2.1 Array Constructors.

  • The fn:function-lookup function can be called to discover functions that are present in the dynamic context.

  • The fn:load-xquery-module function can be called to load functions dynamically from an external XQuery library module.

  • Some system functions such as fn:random-number-generator and fn:op return a function item as their result.

These constructs are described in detail in the following sections, or in [XQuery and XPath Functions and Operators 4.0].

4.6.2.1 Dynamic Function Calls
[158]    DynamicFunctionCall    ::=    PostfixExpr PositionalArgumentList
[160]    PositionalArgumentList    ::=    "(" PositionalArguments? ")"
[161]    PositionalArguments    ::=    Argument ("," Argument)*
[181]    Argument    ::=    ExprSingle | ArgumentPlaceholder
[182]    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 4.6.2.2 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.

4.6.2.2 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 4.6.2.3 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 item F 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 F 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 F’s signature by applying the coercion rules, resulting in a converted argument value

  4. If F is a map, it is evaluated as described in 4.16.1.2 Map Lookup using Function Call Syntax.

  5. If F is an array, it is evaluated as described in 4.16.2.2 Array Lookup using Function Call Syntax.

  6. If F’s body is an XQuery 4.0 and XPath 4.0 expression (for example, if F is a user-defined function or an anonymous function, or a partial application of such a function):

    1. F’s body is evaluated. The static context for this evaluation is the static context of the XQuery 4.0 and XPath 4.0 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the module InlineFunctionExpr that contains the FunctionBody, and making the following changes:

      • The focus (context value, context position, and context size) is absentDM31.

      • 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.

      • F’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 F 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 F. 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 dynamic error [err:XPDY0002]:

    let $vat := function() { @vat + @price }
    return shop/article/$vat()

    Instead, the context value can be used as an argument to the anonymous function:

    let $vat := function($art) { $art/@vat + $art/@price }
    return shop/article/$vat(.)

    Alternatively, the value can be referenced as a nonlocal variable binding:

    let $ctx := shop/article,
    $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(shop/article)
  7. If F’s implementation is not an XQuery 4.0 and XPath 4.0 expression (e.g., F is a system function or 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 4.6.1.1 Static Function Call Syntax).

    Errors may be raised in the same way.

4.6.2.3 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 definition F to be partially applied is determined in the same way as for a static function call without placeholders, as described in 4.6.1.1 Static Function Call Syntax. For this purpose an ArgumentPlaceholder contributes to the count of arguments.

  2. The parameters of F 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.

  4. The result is a partially applied function having the following properties (which are defined in Section 2.8.1 Functions DM31):

    • name: Absent.

    • identity: A new function identity distinct from the identity of any other function item.

      Note:

      See also 4.6.2.7 Function Identity.

    • arity: The number of placeholders in the function call.

    • parameter names: The names of the parameters of F 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 F 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 F.

      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 F.

    • 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 item F to be partially applied is determined in the same way as for a dynamic function call without placeholders, as described in 4.6.2.1 Dynamic Function Calls. For this purpose an ArgumentPlaceholder contributes to the count of arguments.

  2. The parameters of F 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.

  4. The result of the partial function application is a partially applied function with the following properties (which are defined in Section 2.8.1 Functions DM31):

    • name: Absent.

    • arity: the number of placeholders in the function call.

    • parameter names: The names of parameters in F 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 F, 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 F.

    • captured context: the captured context of F, 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 := map {"A": 1, "B": 2}(?)
return $a("A")
4.6.2.4 Named Function References
[211]    NamedFunctionRef    ::=    EQName "#" IntegerLiteral /* xgc: reserved-function-names */
[272]    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 definition FD.

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".

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 item FI obtained from FD as follows:

  • The name of FI is the name of FD.

  • The identity of FI is as follows:

    • 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 2.9.1 Function ItemsDM40) 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 scopesFO40: 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 nondeterministicFO40. 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.

    Note:

    See also 4.6.2.7 Function Identity.

  • The parameter names of FI are the first A parameter names of FD, where A is the required arity.

  • The signature of FI is formed from the required types of the first A parameters of FD, and the function result type of FD.

  • The implementation of FI is the implementation of FD.

  • The captured context of FI 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. Although the base function referred to may be variadic, the result of evaluating the function reference is a function that has fixed arity. In effect, the result of evaluating my:func#3 is the same as the result of evaluating the inline function expression function($x, $y, $z){my:func($x, $y, $z)}, except that the returned function has a name (it retains the name my:func).

4.6.2.5 Inline Function Expressions
[212]    InlineFunctionExpr    ::=    Annotation* ("function" | "fn") FunctionSignature? FunctionBody
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[29]    AnnotationValue    ::=    StringLiteral | ("-"? NumericLiteral) | ("true" "(" ")") | ("false" "(" ")")
[36]    FunctionSignature    ::=    "(" ParamList? ")" TypeDeclaration?
[39]    ParamList    ::=    Param ("," Param)*
[40]    Param    ::=    "$" EQName TypeDeclaration?
[229]    TypeDeclaration    ::=    "as" SequenceType
[41]    FunctionBody    ::=    EnclosedExpr

[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 4.6.2.6 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 and XPath 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 absentDM31.

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 with the following properties (as defined in Section 2.8.1 Functions DM31):

  • name: Absent.

  • identity: A new function identity distinct from the identity of any other function item.

    Note:

    See also 4.6.2.7 Function Identity.

  • parameter names: The parameter names in the InlineFunctionExpr’s ParamList.

  • signature: A FunctionTest constructed from the Annotations and SequenceTypes 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.

  • implementation: 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 absentDM31. 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

4.6.2.6 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 arrow operator and dt-mapping-arrow operator. For example, $s => tokenize() =!> fn { `"{.}"` }() first tokenizes the string $s, then wraps each token in double quotation marks.

The expression function{EXPR} (or fn{EXPR}) is a syntactic shorthand for the expression function($Z as item()*) as item()* {$Z!(EXPR)}, where $Z is a variable name that is otherwise unused. Note that the function body (EXPR) is evaluated with a fixed focus: the context position and context size will always be 1 (one).

Editorial note 2023-09-14
TODO: The above no longer works. We don't currently have any construct (other than this one) that sets the context value to something other than a singleton.
4.6.2.7 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 4.6.2.4 Named Function References.

  • An optimizer is permitted to rewrite expressions in such a way that repeated evaluation is avoided if it can be established that the result will be the same each time, and this may be done without consideration of function identity. For example, if the expression contains(?, "e") appears within the body of a for expression, 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, optimizers are allowed to replace any expression with an equivalent expression; for example, count(?) may be rewritten as count#1.

4.6.3 Coercion Rules

[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.

The coercion rules are applied to a supplied value V and a required sequence type T as follows:

  • If XPath 1.0 compatibility mode is true and V is not of the required type T, then the following conversions are applied sequentially to V:

    1. If T requires a single item or optional single item (examples: xs:string, xs:string?, xs:untypedAtomic, xs:untypedAtomic?, node(), node()?, item(), item()?), then V is effectively replaced by V[1].

    2. If T is xs:string or xs:string?, then V is effectively replaced by fn:string(V).

      Note:

      This rule does not apply where T is derived from xs:string or xs:string?, because derived types did not arise in XPath 1.0.

    3. If T is xs:double or xs:double?, then V is effectively replaced by fn:number(V).

      Note:

      This rule does not apply where T is derived from xs:double or xs:double?, because derived types did not arise in XPath 1.0.

    Note:

    The special rules for XPath 1.0 compatibility mode are used for converting the arguments of a static function call, and in certain XSLT constructs. They are not invoked in other contexts such as dynamic function calls, for converting the result of an inline function to its required type, for partial function application, or for implicit function calls such as occur when evaluating functions such as fn:for-each and fn:filter.

  • If T is a SequenceType whose ItemType is a generalized atomic type (possibly with an occurrence indicator *, +, or ?), then the following conversions are applied, in order:

    Note:

    Enumeration types are generalized atomic types, so these rules apply.

    1. Atomization is applied to the given value, resulting in a sequence of atomic values.

    2. Each item in the atomic sequence that is of type xs:untypedAtomic is cast to the expected generalized atomic type. If the expected atomic type is an EnumerationType, the value is cast to xs:string . If the item is of type xs:untypedAtomic and the expected type is namespace-sensitive, a type error [err:XPTY0117] is raised.

    3. For each numeric item in the atomic sequence that can be promoted to the expected atomic type using numeric promotion as described in B.1 Type Promotion, the promotion is done.

      Note:

      Numeric promotion is performed only when the required type is xs:double or xs:float (perhaps with an occurrence indicator). It is not performed when the required type is derived from xs:double or xs:float.

    4. For each item of type xs:anyURI in the atomic sequence that can be promoted to the expected atomic type using URI promotion as described in B.1 Type Promotion, the promotion is done.

      Note:

      Promotion of xs:anyURI values is performed only when the required type is xs:string (perhaps with an occurrence indicator). It is not performed when the required type is derived from xs:string.

    5. If T is a sequence type whose item type is an atomic type D, where D is derived from some primitive type P, then any atomic value A in the atomic sequence is relabeled as an instance of D if it satisfies all the following conditions:

      1. A is an instance of P.

      2. A is not an instance of D.

      3. The datumDM40 of A is within the value space of D.

      Relabeling an atomic value changes the type annotation but not the datumDM40. 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.

      Note:

      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 can be defined as xs:positiveInteger rather than xs:integer. To enable this to be done without breaking backwards compatibility in respect of error behavior, system functions in many cases define custom error codes to be raised where relabeling of argument values fails.

      Note:

      Numeric promotion and xs:anyURI promotion occur only when T is a primitive type (xs:double, xs:float, or xs:string). Relabeling occurs only when T is a derived type. Promotion and relabeling are therefore never combined.

    6. If T is a sequence type whose item type is a pure union type U, then any atomic value A in the atomic sequence is relabeled as an instance of some member type M in the transitive membership of U if M satisfies all the conditions for relabeling defined in the previous rule, and if it is the first member type in the transitive membership of U to satisfy those conditions. For example, if T is the type union(xs:negativeInteger, xs:positiveInteger)* and the supplied value is the sequence (20, -20), then the first item 20 is relabeled as type xs:positiveInteger and the second item -20is relabeled as type xs:negativeInteger.

      Note:

      This rule also ensures that if the required type is enum("red", "green", "blue") and the supplied value is "green", then the supplied value will be accepted, and will be relabeled as an instance of the derived atomic type enum("green").

  • If T is a RecordTest (possibly with an occurrence indicator *, +, or ?), then V must be a map or sequence of maps, and the values of any entries in these maps whose keys correspond to field declarations in the RecordTest are converted to the required type defined by that field declaration, by applying these rules recursively (but with XPath 1.0 compatibility mode treated as false).

    For example, if the required type is record(longitude as xs:double, latitude as xs:double) and the supplied value is map{"longitude": 0, "latitude":53.2}, then the map is converted to map{"longitude": 0.0e0, "latitude": 53.2e0}.

  • If the expected type is a TypedFunctionTest (possibly with an occurrence indicator *, +, or ?), function coercion is applied to each function in the given value.

    Note:

    Maps and arrays are functions, so function coercion applies to them as well.

  • If, after the above conversions, the resulting value does not match the expected type T 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.

  • 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. Two sequence types are considered to be substantively disjoint if (a) neither is a subtype of the other (see 3.7.1 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, 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: this case can always be reported as a static error.

4.6.4 Function Coercion

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, function coercion proceeds as follows:

  1. If F has higher arity than the expected type, a type error is raised [err:XPTY0004]

  2. If F has lower arity than the expected type, 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 the expected type 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.

    TODO: this change to fn:filter has not yet been made.

  3. Function coercion then returns a new function item with the following properties (as defined in Section 2.8.1 Functions DM31):

    • name: The name of F (if not absent).

    • identity: A new function identity distinct from the identity of any other function item.

      Note:

      See also 4.6.2.7 Function Identity.

    • parameter names: The parameter names of F.

    • signature: Annotations is set to the annotations of F. TypedFunctionTest 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.

If the result of invoking the new function would necessarily result in a type error, that error may be raised during function coercion. It is implementation dependent whether this happens or not.

These rules have the following consequences:

  • SequenceType matching of the function’s arguments and result are delayed until that function is called.

  • 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.

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:

Although the semantics of function coercion are specified in terms of wrapping the functions, static typing will often be able to reduce the number of places where this is actually necessary.

Since maps and arrays are also functions in XQuery 4.0 and XPath 4.0, function coercion applies to them as well. For instance, consider the following expression:

let $m := map {
  "Monday" : true(),
  "Wednesday" : true(),
  "Friday" : true(),
  "Saturday" : false(),
  "Sunday" : false()
},
$days := ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
return filter($days,$m)

The map $m has a function signature of function(xs:anyAtomicType) as item()*. When the fn:filter() function is called, the following occurs to the map:

  1. The map $m is treated as function($f), equivalent to map:get($m,?).

  2. The coercion rules result in applying function coercion to $f, wrapping $f in a new function ($p) with the signature function(item()) as xs:boolean.

  3. $p is matched against the SequenceType function(item()) as xs:boolean, and succeeds.

  4. When $p is called by fn:filter(), coercion and SequenceType matching rules are applied to the argument, resulting in an item() value ($a) or a type error.

  5. $f is called with $a, which returns an xs:boolean or the empty sequence.

  6. $p applies coercion rule and SequenceType matching to the result sequence from $f. When the result is an xs:boolean the SequenceType matching succeeds. When it is an empty sequence (such as when $m does not contain a key for "Tuesday"), SequenceType matching results in a type error [err:XPTY0004], since the expected type is xs:boolean and the actual type is an empty sequence.

Consider the following expression:

let $m := map {
   "Monday" : true(),
   "Tuesday" : false(),
   "Wednesday" : true(),
   "Thursday" : false(),
   "Friday" : true(),
   "Saturday" : false(),
   "Sunday" : false()
}
let $days := ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
return filter($days,$m)

The result of the expression is the sequence ("Monday", "Wednesday", "Friday")

4.7 Path Expressions

[141]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* xgc: leading-lone-slash */
[142]    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 4.7.4 Steps.

4.7.1 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.

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 or namespace nodes.

Note:

A // on its own is not allowed by the grammar.

4.7.2 Relative Path Expressions

[142]    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 4.7.7 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 4.7.3 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.

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, 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 /*.

4.7.3 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. If ordering mode is ordered, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent order.

  2. If every evaluation of E2 returns a (possibly empty) sequence of non-nodes, these sequences are concatenated, in order, and returned. If ordering mode is ordered, the The returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2 . ; otherwise the order of the returned sequence is implementation-dependent.

  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 (forming the union with an empty sequence ($R | ()) has the effect of eliminating duplicates and sorting nodes into document order):

E1/E2 ::= let $R := E1!E2
  return
    if (every $r in $R satisfies $r instance of node())
    then ($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 4.25 Simple map operator (!).

4.7.4 Steps

[143]    StepExpr    ::=    PostfixExpr | AxisStep
[144]    AxisStep    ::=    (ReverseStep | ForwardStep) PredicateList
[145]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbrevForwardStep
[148]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbrevReverseStep
[164]    PredicateList    ::=    Predicate*

[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 4.4 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. if ordering mode is ordered, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent 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 4.7.7 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 4.7.4.1 Axes. The available node tests are described in 4.7.4.2 Node Tests. Examples of steps are provided in 4.7.6 Unabbreviated Syntax and 4.7.7 Abbreviated Syntax.

4.7.4.1 Axes
[146]    ForwardAxis    ::=    ("child" "::")
| ("descendant" "::")
| ("attribute" "::")
| ("self" "::")
| ("descendant-or-self" "::")
| ("following-sibling" "::")
| ("following" "::")
| ("namespace" "::")
[149]    ReverseAxis    ::=    ("parent" "::")
| ("ancestor" "::")
| ("preceding-sibling" "::")
| ("preceding" "::")
| ("ancestor-or-self" "::")

XPath defines a full set of axes for traversing documents, but a host language may define a subset of these axes. The following axes are defined:

XQuery supports the following axes:

  • The child axis contains the children of the context node, which are the nodes returned by the Section 5.3 children Accessor DM31.

    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, namespace, 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).

  • The parent axis contains the sequence returned by the Section 5.11 parent Accessor DM31, 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).

    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 following-sibling axis contains the context node’s following siblings, 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.

  • the preceding-sibling axis contains the context node’s preceding siblings, 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.

  • 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.

  • 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.

  • The attribute axis contains the attributes of the context node, which are the nodes returned by the Section 5.1 attributes Accessor DM31 ; the axis will be empty unless the context node is an element.

  • The self axis contains just the context node itself.

  • The descendant-or-self axis contains the context node and the descendants of the context 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.

  • The namespace axis contains the namespace nodes of the context node, which are the nodes returned by the Section 5.7 namespace-nodes Accessor DM31; this axis is empty unless the context node is an element node. The namespace axis is deprecated as of XPath 2.0. If XPath 1.0 compatibility mode is true, the namespace axis must be supported. If XPath 1.0 compatibility mode is false, then support for the namespace axis is implementation-defined. An implementation that does not support the namespace axis when XPath 1.0 compatibility mode is false must raise a static error [err:XPST0010] if it is used. Applications needing information about the in-scope namespaces of an element should use the functions Section 10.2.6 fn:in-scope-prefixes FO31, and Section 10.2.5 fn:namespace-uri-for-prefix FO31.

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, and preceding-sibling axes are reverse axes; all other axes are forward axes. The ancestor, descendant, following, preceding and self axes partition a document (ignoring attribute and namespace 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 the namespace axis, the principal node kind is namespace.

  • For all other axes, the principal node kind is element.

4.7.4.2 Node Tests

[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.]

[151]    NodeTest    ::=    UnionNodeTest | SimpleNodeTest
[152]    UnionNodeTest    ::=    "(" SimpleNodeTest ("|" SimpleNodeTest)* ")"
[153]    SimpleNodeTest    ::=    KindTest | NameTest
[154]    NameTest    ::=    EQName | Wildcard
[155]    Wildcard    ::=    "*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
[272]    EQName    ::=    QName | URIQualifiedName
[235]    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 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 an 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 3.4 Sequence Types and 3.5 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 content consists of a single element node that satisfies the kind test element(book), interleaved with zero or more comments and processing instructions.

4.7.4.3 Implausible Axis Steps

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.

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.

4.7.5 Predicates within Steps

[144]    AxisStep    ::=    (ReverseStep | ForwardStep) PredicateList
[164]    PredicateList    ::=    Predicate*
[165]    Predicate    ::=    "[" Expr "]"

A predicate within a Step 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.

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.

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]

Note:

When using predicates with a sequence of nodes selected using a reverse axis, the context positions for such a sequence are assigned in reverse document order. For example, preceding::foo[1] returns the first qualifying foo element in reverse document order, because the predicate is part of an axis step using a reverse axis. By contrast, (preceding::foo)[1] returns the first qualifying foo element in document order, because the parentheses cause (preceding::foo) to be parsed as a primary expression in which context positions are assigned in document order. Similarly, ancestor::*[1] returns the nearest ancestor element, because the ancestor axis is a reverse axis, whereas (ancestor::*)[1] returns the root element (first ancestor 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 (when in ordered mode) 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. 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.

4.7.6 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 4.7.7 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.

4.7.7 Abbreviated Syntax

[147]    AbbrevForwardStep    ::=    ("@" NodeTest) | SimpleNodeTest
[150]    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 NamespaceNodeTest then a static error is raised [err:XQST0134]. then the default axis is namespace, but in an implementation that does not support the namespace axis, an 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 expression, is a primary expression, and is described in 4.3.4 Context Value Expression.

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.

4.8 Sequence Expressions

XQuery 4.0 and XPath 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).

4.8.1 Sequence Concatenation

[46]    Expr    ::=    ExprSingle ("," 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.

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)

4.8.2 Range Expressions

[116]    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)

4.8.3 Combining Node Sequences

[120]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[121]    IntersectExceptExpr    ::=    InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*

XQuery 4.0 and XPath 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 ordering mode is ordered, the resulting sequence is returned in document order; otherwise it is returned in implementation-dependent 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 ordering mode is ordered. 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 14 Functions and operators on sequences FO31 for functions defined on sequences.

4.9 Arithmetic Expressions

XQuery 4.0 and XPath 4.0 provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.

[117]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[118]    MultiplicativeExpr    ::=    OtherwiseExpr ( ("*" | "×" | "div" | "÷" | "idiv" | "mod") OtherwiseExpr )*
[127]    UnaryExpr    ::=    ("-" | "+")* ValueExpr
[128]    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.

If XPath 1.0 compatibility mode is true, 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 the xs:double value NaN, 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, any items after the first item in the sequence are discarded.

  4. If the atomized operand is now an instance of type xs:boolean, xs:string, xs:decimal (including xs:integer), xs:float, or xs:untypedAtomic, then it is converted to the type xs:double by applying the fn:number function. (Note that fn:number returns the value NaN if its operand cannot be converted to a number.)

If XPath 1.0 compatibility mode is false, each 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]FO31

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 value 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 and XPath 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.

4.10 String Expressions

This section describes several ways of constructing strings.

4.10.1 String Concatenation Expressions

[115]    StringConcatExpr    ::=    RangeExpr ( "||" RangeExpr )*

String concatenation expressions allow the string representations of values to be concatenated. In XQuery 4.0 and XPath 4.0, $a || $b is equivalent to fn:concat($a, $b). The following expression evaluates to the string concatenate:

() || "con" || ("cat", "enate")

4.10.2 String Templates

[220]    StringTemplate    ::=    "`" (StringTemplateFixedPart | StringTemplateVariablePart)* "`" /* ws: explicit */
[221]    StringTemplateFixedPart    ::=    ((Char - ('{' | '}' | '`')) | "{{" | "}}" | "``")* /* ws: explicit */
[222]    StringTemplateVariablePart    ::=    EnclosedExpr /* ws: explicit */
[42]    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 a grave accent (x60), 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 curly bracket within a StringLiteral or within a comment.

    Currently no XPath expression starts with an opening curly bracket, so the use of {{ creates no ambiguity. If an enclosed expression ends with a closing curly bracket, no whitespace is required between this and the closing delimiter.

    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:

    • a left curly bracket must be written as {{

    • a right curly bracket must be written as }}.

    • a back-tick must be written as ``.

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 values.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic value 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 StringConstructor, 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. Although the token ``[ is not used in XPath, it is reserved for compatibility reasons, and must be rejected as syntactically invalid. 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.

4.10.3 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 and XPath 4.0.

[223]    StringConstructor    ::=    "``[" StringConstructorContent "]``" /* ws: explicit */
[224]    StringConstructorContent    ::=    StringConstructorChars (StringInterpolation StringConstructorChars)* /* ws: explicit */
[225]    StringConstructorChars    ::=    (Char* - (Char* ('`{' | ']``') Char*)) /* ws: explicit */
[226]    StringInterpolation    ::=    "`{" Expr? "}`" /* ws: explicit */

Note:

String templates (see 4.10.2 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 braces, 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:

map {
  "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
}

4.11 Comparison Expressions

Comparison expressions allow two values to be compared. XQuery 4.0 and XPath 4.0 provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.

[114]    ComparisonExpr    ::=    StringConcatExpr ( (ValueComp
| GeneralComp
| NodeComp) StringConcatExpr )?
[133]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[132]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[134]    NodeComp    ::=    "is" | "<<" | ">>"

Note:

When an XPath expression is written within an XML document, the XML escaping rules for special characters must be followed; thus < must be written as &lt;.

4.11.1 Value Comparisons

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 value, 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")

4.11.2 General Comparisons

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.

If XPath 1.0 compatibility mode is true, a general comparison is evaluated by applying the following rules, in order:

  1. If either operand is a single atomic value that is an instance of xs:boolean, then the other operand is converted to xs:boolean by taking its effective boolean value.

  2. Atomization is applied to each operand. After atomization, each operand is a sequence of atomic values.

  3. If the comparison operator is <, <=, >, or >=, then each item in both of the operand sequences is converted to the type xs:double by applying the fn:number function. (Note that fn:number returns the value NaN if its operand cannot be converted to a number.)

  4. The result of the comparison is true if and only if there is a pair of atomic values, 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 values 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]FO31

    1. If at least one of the two atomic values is an instance of a numeric type, then both atomic values are converted to the type xs:double by applying the fn:number function.

    2. If at least one of the two atomic values is an instance of xs:string, or if both atomic values are instances of xs:untypedAtomic, then both atomic values are cast to the type xs:string.

    3. If one of the atomic values is an instance of xs:untypedAtomic and the other is not an instance of xs:string, xs:untypedAtomic, or any numeric type, then the xs:untypedAtomic value is cast to the dynamic type of the other value.

    4. After performing the conversions described above, the atomic values 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.

If XPath 1.0 compatibility mode is false, a 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 values.

  2. The result of the comparison is true if and only if there is a pair of atomic values, 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 values 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]FO31

    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 values are instances of xs:untypedAtomic, then the values are cast to the type xs:string.

    2. If exactly one of the atomic values 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 values 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.

4.11.3 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) 3.1] 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"]

4.12 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.

[112]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[113]    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 2.5.3 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 = true EBV2 = false error in EBV2
EBV1 = true true false error
EBV1 = false false false either false or error if XPath 1.0 compatibility mode is true, then false; otherwise either false or error.
error in EBV1 error either false or error if XPath 1.0 compatibility mode is true, then error; otherwise either false or error. error

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 = true EBV2 = false error in EBV2
EBV1 = true true true either true or error if XPath 1.0 compatibility mode is true, then true; otherwise either true or error.
EBV1 = false true false error
error in EBV1 either true or error if XPath 1.0 compatibility mode is true, then error; otherwise either true or error. error error

If XPath 1.0 compatibility mode is true, the order in which the operands of a logical expression are evaluated is effectively prescribed. Specifically, it is defined that when there is no need to evaluate the second operand in order to determine the result, then no error can occur as a result of evaluating the second operand.

If XPath 1.0 compatibility mode is false, the order in which the operands of a logical expression are evaluated is implementation-dependent. In this case, 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:

In addition to and- and or-expressions, XQuery 4.0 and XPath 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.

4.13 Node Constructors

XQuery provides node constructors that can create XML nodes within a query.

[183]    NodeConstructor    ::=    DirectConstructor
| ComputedConstructor
[184]    DirectConstructor    ::=    DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
[185]    DirElemConstructor    ::=    "<" QName DirAttributeList ("/>" | (">" DirElemContent* "</" QName S? ">")) /* ws: explicit */
[190]    DirElemContent    ::=    DirectConstructor
| CDataSection
| CommonContent
| ElementContentChar
[284]    ElementContentChar    ::=    (Char - [{}<&])
[191]    CommonContent    ::=    PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
[196]    CDataSection    ::=    "<![CDATA[" CDataSectionContents "]]>" /* ws: explicit */
[197]    CDataSectionContents    ::=    (Char* - (Char* ']]>' Char*)) /* ws: explicit */
[186]    DirAttributeList    ::=    (S (QName S? "=" S? DirAttributeValue)?)* /* ws: explicit */
[187]    DirAttributeValue    ::=    ('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
[188]    QuotAttrValueContent    ::=    QuotAttrContentChar
| CommonContent
[189]    AposAttrValueContent    ::=    AposAttrContentChar
| CommonContent
[285]    QuotAttrContentChar    ::=    (Char - ["{}<&])
[286]    AposAttrContentChar    ::=    (Char - ['{}<&])
[282]    EscapeQuot    ::=    '""' /* ws: explicit */
[283]    EscapeApos    ::=    "''" /* ws: explicit */
[42]    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.

4.13.1 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, it is interpreted according to the default namespace for elements and types.

Note:

Both the statically known namespaces and the default namespace for elements and types 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) 3.1]. 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 braces { } 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 curly braces to denote enclosed expressions, some convention is needed to denote a curly brace used as an ordinary character. For this purpose, a pair of identical curly brace characters within the content of an element or attribute are interpreted by XQuery as a single curly brace character (that is, the pair "{{" represents the character { and the pair "}}" represents the character }.) Alternatively, the character references &#x7b; and &#x7d; can be used to denote curly brace characters. A single left curly brace ({) is interpreted as the beginning delimiter for an enclosed expression. A single right curly brace (}) without a matching left curly brace is treated as a static error [err:XPST0003].

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.

4.13.1.1 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 4.13.1.2 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) 3.1]. 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.

    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 values.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic value 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.

4.13.1.2 Namespace Declaration Attributes

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 4.13.1.1 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 the namespace URI specifies the default namespace for elements and types of the constructor expression (overriding any existing default), and is added (with no prefix) to the in-scope namespaces of the constructed element (overriding any existing binding of the zero-length prefix).

    If the namespace URI is a zero-length string then the default namespace for elements and types of the constructor expression is set to absentDM31, and any no-prefix namespace binding is removed from the in-scope namespaces of the constructed element.

  • 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 for elements and types to http://example.org/animals:

    <cat xmlns="http://example.org/animals">
      <breed>Persian</breed>
    </cat>
  • 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>
4.13.1.3 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 values. 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 4.13.1.4 Boundary Whitespace for the definition of boundary whitespace.)

    2. Predefined entity references and character references are expanded into their referenced strings, as described in 4.3.1 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 4.13.1 Direct Element Constructors or 4.13.2 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 values returned by an enclosed expression, a new text node is constructed, containing the result of casting each atomic value 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 4.13.1 Direct Element Constructors.

    2. parent is set to empty.

    3. attributes consist of all the attributes specified in the start tag as described in 4.13.1.1 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 4.13.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 4.13.4 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".

4.13.1.4 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 values 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.

4.13.2 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.

[194]    DirPIConstructor    ::=    "<?" PITarget (S DirPIContents)? "?>" /* ws: explicit */
[195]    DirPIContents    ::=    (Char* - (Char* '?>' Char*)) /* ws: explicit */
[192]    DirCommentConstructor    ::=    "<!--" DirCommentContents "-->" /* ws: explicit */
[193]    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.

4.13.3 Computed Constructors

[198]    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, and processing instruction 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 4.13.1 Direct Element Constructors:

element book {
   attribute isbn {"isbn-0060229357" },
   element title { "Harold and the Purple Crayon"},
   element author {
      element first { "Crockett" },
      element last {"Johnson" }
   }
}
4.13.3.1 Computed Element Constructors
[200]    CompElemConstructor    ::=    "element" (EQName | ("{" Expr "}")) EnclosedContentExpr
[272]    EQName    ::=    QName | URIQualifiedName
[201]    EnclosedContentExpr    ::=    EnclosedExpr
[42]    EnclosedExpr    ::=    "{" Expr? "}"

[Definition: A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.]

If the keyword element is followed by an EQName, it is expanded to an expanded QName as follows: if the EQName has a BracedURILiteral it is expanded using the specified URI; if the EQName is a lexical QName with a namespace prefix it is expanded using the statically known namespaces; if the EQName is a lexical QName without a prefix it 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. . The resulting expanded QName is used as the node-name property of the constructed element node. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

If the keyword element is followed by a name expression, the name expression 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 value 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 QName as follows:

    1. Leading and trailing whitespace is removed.

    2. If the value is an unprefixed NCName, it is interpreted according to the default namespace for elements and types.

    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.

    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). If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

A dynamic 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 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 4.13.1.3 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 lexical QName or name expression, 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 4.13.4 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($e) is xs:QName?, denoting zero or one QName. Therefore, if the Static Typing Feature is in effect, the above example raises a static type error, since the name expression in a computed element constructor is required to return exactly one string or QName. In order to avoid the static type error, the name expression fn:node-name($e) could be rewritten as fn:exactly-one(fn:node-name($e)). If the Static Typing Feature is not in effect, 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>

Note:

As in the previous example, if the Static Typing Feature is in effect, the enclosed expression that computes the element name in the above computed element constructor must be wrapped in a call to the fn:exactly-one function in order to avoid a static type error.

Additional examples of computed element constructors can be found in J.3 Recursive Transformations.

4.13.3.2 Computed Attribute Constructors
[202]    CompAttrConstructor    ::=    "attribute" (EQName | ("{" Expr "}")) EnclosedExpr
[272]    EQName    ::=    QName | URIQualifiedName
[42]    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.

If the keyword attribute is followed by an EQName, it is expanded to an expanded QName as follows:

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:

  1. Atomization is applied to the result of the name expression. If the result of atomization is not a single atomic value 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 QName as 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.

    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. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

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 values. (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 value 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".

4.13.3.3 Document Node Constructors
[199]    CompDocConstructor    ::=    "document" EnclosedExpr
[42]    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 4.13.1.3 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.

4.13.3.4 Text Node Constructors
[207]    CompTextConstructor    ::=    "text" EnclosedExpr
[42]    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 values.

  2. If the result of atomization is an empty sequence, no text node is constructed. Otherwise, each atomic value 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"}
4.13.3.5 Computed Processing Instruction Constructors
[209]    CompPIConstructor    ::=    "processing-instruction" (NCName | ("{" Expr "}")) EnclosedExpr
[42]    EnclosedExpr    ::=    "{" Expr? "}"

A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity.

If the keyword processing-instruction is followed by an NCName, that NCName is used as the target property of the constructed node. If the keyword processing-instruction is followed by a name expression, the name expression 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 value 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 values. (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 value 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",
    $content := "beep"
return processing-instruction {$target} {$content}

The processing instruction node constructed by this example might be serialized as follows:

<?audio-output beep?>
4.13.3.6 Computed Comment Constructors
[208]    CompCommentConstructor    ::=    "comment" EnclosedExpr
[42]    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 values.

  2. If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value 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.-->
4.13.3.7 Computed Namespace Constructors
[203]    CompNamespaceConstructor    ::=    "namespace" (Prefix | EnclosedPrefixExpr) EnclosedURIExpr
[204]    Prefix    ::=    NCName
[205]    EnclosedPrefixExpr    ::=    EnclosedExpr
[206]    EnclosedURIExpr    ::=    EnclosedExpr
[42]    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 empty.

If the constructor specifies a Prefix, it is used as the prefix for the namespace node.

If the constructor specifies a PrefixExpr, the prefix expression is evaluated as follows:

  1. Atomization is applied to the result of the PrefixExpr.

  2. If the result of atomization is an empty sequence or a single atomic value 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 value, 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 value 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. As defined in the data model, the name of the node is the prefix, the string value of the node is the URI, the relative order of nodes that share no common ancestor is implementation dependent, and the relative order of namespace nodes that share a parent is also 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>

4.13.4 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 2.3.4 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>

4.14 For Expressions

XPath provides an iteration facility called a for expression. It can be used to iterate over the items of a sequence, or the members of an array.

[50]    ForExpr    ::=    SimpleForClause SimpleReturnClause
[51]    SimpleForClause    ::=    "for" SimpleForBinding (("for" | ",") SimpleForBinding)*
[52]    SimpleForBinding    ::=    "member"? "$" VarName "in" ExprSingle
[53]    SimpleReturnClause    ::=    "return" ExprSingle

A for expression is evaluated as follows:

  1. If the for expression uses multiple variables, it is first expanded to a set of nested for expressions, each of which uses only one variable. More specifically, every separating comma or for keyword is replaced by return for.

    For example, the expression for $x in X, $y in Y return $x + $y is expanded to for $x in X return for $y in Y return $x + $y.

    Similarly, the expression for member $x in X for member $y in Y return $x + $y is expanded to for member $x in X return for member $y in Y return $x + $y.

  2. In a single-variable for expression, the variable is called the range variable, the expression that follows the in keyword is called the binding expression, and the expression that follows the return keyword is called the return expression.

    [Definition: The result of evaluating the binding expression in a for expression is called the binding collection ].

  3. When the member keyword is absent, the result of the single-variable for expression is obtained by evaluating the return expression once for each item in the binding collection, with the range variable bound to that item. The resulting sequences are concatenated (as if by the comma operator) in the order of the items in the binding collection from which they were derived.

  4. When the member keyword is present, the value of the binding collection must be a single array. Otherwise, a type error is raised: [err:XPTY0141]. The result of the single-variable for member expression is obtained by evaluating the return expression once for each member of that array, with the range variable bound to that member (recall that this can be any sequence, not necessarily a single item). The resulting sequences are concatenated (as if by the comma operator) in the order of the members of the binding collection from which they were derived.

    Note that the result is a sequence, not an array.

The following example illustrates the use of a for expression in restructuring an input document. The example is based on the following input:

<bib>
  <book>
    <title>TCP/IP Illustrated</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Advanced Programming in the Unix Environment</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Data on the Web</title>
    <author>Abiteboul</author>
    <author>Buneman</author>
    <author>Suciu</author>
  </book>
</bib>

The following example transforms the input document into a list in which each author’s name appears only once, followed by a list of titles of books written by that author. This example assumes that the context value is the bib element in the input document.

for $a in distinct-values(book/author)
return ((book/author[. = $a])[1], book[author = $a]/title)

The result of the above expression consists of the following sequence of elements. The titles of books written by a given author are listed after the name of the author. The ordering of author elements in the result is implementation-dependent due to the semantics of the fn:distinct-values function.

<author>Stevens</author>
<title>TCP/IP Illustrated</title>
<title>Advanced Programming in the Unix environment</title>
<author>Abiteboul</author>
<title>Data on the Web</title>
<author>Buneman</author>
<title>Data on the Web</title>
<author>Suciu</author>
<title>Data on the Web</title>

The following example illustrates a for expression containing more than one variable:

for $i in (10, 20),
    $j in (1, 2)
return ($i + $j)

The result of the above expression, expressed as a sequence of numbers, is as follows: 11, 12, 21, 22

The scope of a variable bound in a for expression comprises all subexpressions of the for expression that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following example illustrates how a variable binding may reference another variable bound earlier in the same for expression:

for $x in $z, $y in f($x)
return g($x, $y)

The following example illustrates processing of an array.

for member $map in parse-json('[{"x":1, "y":2}, {"x":10, "y":20}]') return $map!(?x+?y)

The result is the sequence (3, 30).

Note:

The focus for evaluation of the return clause of a for expression is the same as the focus for evaluation of the for expression itself. The following example, which attempts to find the total value of a set of order-items, is therefore incorrect:

sum(for $i in order-item return @price * @qty)

Instead, the expression must be written to use the variable bound in the for clause:

sum(for $i in order-item return $i/@price * $i/@qty)

Note:

XPath 4.0 allows the format:

for $order in //orders
for $line in $order/order-line
return $line/value

primarily because it is familiar to XQuery users, some of whom may regard it as more readable than the XPath 3.1 alternative which uses a comma in place of the second for.

4.15 Let Expressions

XPath allows a variable to be declared and bound to a value using a let expression.

[54]    LetExpr    ::=    SimpleLetClause SimpleReturnClause
[55]    SimpleLetClause    ::=    "let" SimpleLetBinding (("let" | ",") SimpleLetBinding)*
[56]    SimpleLetBinding    ::=    "$" VarName ":=" ExprSingle
[53]    SimpleReturnClause    ::=    "return" ExprSingle

A let expression is evaluated as follows:

  • If the let expression uses multiple variables, it is first expanded to a set of nested let expressions, each of which uses only one variable. Specifically, any separating comma or let keyword is replaced by return let .

    For example, the expression let $x := 4, $y := 3 return $x + $y is expanded to let $x := 4 return let $y := 3 return $x + $y.

    Likewise, the expression let $x := 4 let $y := 3 return $x + $y is expanded to let $x := 4 return let $y := 3 return $x + $y.

  • In a single-variable let expression, the variable is called the range variable, the value of the expression that follows the := symbol is called the binding sequence, and the expression that follows the return keyword is called the return expression. The result of the let expression is obtained by evaluating the return expression with the range variable bound to the binding sequence.

The scope of a variable bound in a let expression comprises all subexpressions of the let expression that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following example illustrates how a variable binding may reference another variable bound earlier in the same let expression:

let $x := doc('a.xml')/*, $y := $x//*
return $y[@value gt $x/@min]

Note:

It is not required that the variables should have distinct names. It is permitted, for example, to write:

let $x := "[A fine romance]"
let $x := substring-after($x, "[")
let $x := substring-before($x, "]")
return upper-case($x)

which returns the result "A FINE ROMANCE". Note that this expression declares three separate variables which happen to have the same name; it should not be read as declaring a single variable and binding it successively to different values.

Note:

XPath 4.0 allows the form using multiple let clauses, as illustrated in the previous example, primarily because it is familiar to XQuery users, some of whom may regard it as more readable than the XPath 3.1 alternative which uses a comma in place of the second and subsequent let keywords.

4.16 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 and XPath 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 and XPath 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 and XPath 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 Maps and Arrays FO31, 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.

4.16.1 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.]

4.16.1.1 Map Constructors

A Map is created using a MapConstructor.

[213]    MapConstructor    ::=    "map" "{" (MapConstructorEntry ("," MapConstructorEntry)*)? "}"
[214]    MapConstructorEntry    ::=    MapKeyExpr ":" MapValueExpr
[215]    MapKeyExpr    ::=    ExprSingle
[216]    MapValueExpr    ::=    ExprSingle

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 map{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 map{a :b} or map{a: b} will prevent this, resulting in the intended parse.

Similarly, consider these three expressions:

    map{a:b:c}
    map{a:*:c}
    map{*: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 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 value. 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 values K1 and K2 have the same key value if fn:atomic-equal(K1, K2) returns true, as specified in Section 18.2.1 fn:atomic-equalFO40 ] If two or more entries have the same key value then a dynamic error is raised [err:XQDY0137].

Example:

The following expression constructs a map with seven entries:

map {
  "Su" : "Sunday",
  "Mo" : "Monday",
  "Tu" : "Tuesday",
  "We" : "Wednesday",
  "Th" : "Thursday",
  "Fr" : "Friday",
  "Sa" : "Saturday"
}

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:

map {
    "book": map {
        "title": "Data on the Web",
        "year": 2000,
        "author": [
            map {
                "last": "Abiteboul",
                "first": "Serge"
            },
            map {
                "last": "Buneman",
                "first": "Peter"
            },
            map {
                "last": "Suciu",
                "first": "Dan"
            }
        ],
        "publisher": "Morgan Kaufmann Publishers",
        "price": 39.95
    }
}
4.16.1.2 Map Lookup using Function Call Syntax

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 17.1.6 map:get FO31.

Examples:

Note:

XQuery 4.0 and XPath 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 4.16.3 The Lookup Operator ("?") for Maps and Arrays 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 4.16.2.2 Array Lookup using Function Call Syntax with map lookups.)

4.16.2 Arrays

4.16.2.1 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.

[217]    ArrayConstructor    ::=    SquareArrayConstructor | CurlyArrayConstructor
[218]    SquareArrayConstructor    ::=    "[" (ExprSingle ("," ExprSingle)*)? "]"
[219]    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 and XPath 4.0 does not provide explicit support for sparse arrays. Use integer-valued maps to represent sparse arrays, e.g. map { 27 : -1, 153 : 17 } .

4.16.2.2 Array Lookup using Function Call Syntax

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 17.3.2 array:get FO31.

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]FO31.

Note:

XQuery 4.0 and XPath 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 4.16.3 The Lookup Operator ("?") for Maps and Arrays for details.

4.16.3 The Lookup Operator ("?") for Maps and Arrays

XQuery 4.0 and XPath 4.0 provides a lookup operator for maps and arrays that is more convenient for some common cases. It provides a terse syntax for simple strings as keys in maps or integers as keys in arrays, supports wildcards, and iterates over sequences of maps and arrays.

4.16.3.1 Unary Lookup
[227]    UnaryLookup    ::=    "?" KeySpecifier
[168]    KeySpecifier    ::=    NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | "*"

Unary lookup is used in predicates (e.g. $map[?name='Mike'] or with the simple map operator (e.g. $maps ! ?name='Mike'). See 4.16.3.2 Postfix Lookup Expressions for the postfix lookup operator.

UnaryLookup returns a sequence of values selected from the context value.

If the context value is anything other than a single item, the semantics of the expression ?KS are defined to be equivalent to the expression . ! ?KS. The remainder of this section therefore explains the semantics on the assumption that the context value is a single item, referred to as the context item.

The context item must be a map or array. If the context item is not a map or an array, a type error is raised [err:XPTY0004].

If the context item is a map:

  1. If the KeySpecifier is an NCName or a StringLiteral , the UnaryLookup operator is equivalent to .(KS), where KS is the value of the NCName or StringLiteral.

  2. If the KeySpecifier is an IntegerLiteral, the UnaryLookup operator is equivalent to .(KS), where KS is the value of the IntegerLiteral.

  3. If the KeySpecifier is a ParenthesizedExpr or a VarRef the UnaryLookup operator is equivalent to the following expression, where KS is the value of the ParenthesizedExpr or VarRef :

    for $k in data(KS)
    return .($k)
  4. If the KeySpecifier is a wildcard (*), the UnaryLookup operator is equivalent to the following expression:

    for $k in map:keys(.)
    return .($k)

    Note:

    The order of keys in map:keys() is implementation-dependent, so the order of values in the result sequence is also implementation-dependent.

If the context item is an array:

  1. If the KeySpecifier is an IntegerLiteral, the UnaryLookup operator is equivalent to .(KS), where KS is the value of the IntegerLiteral.

  2. If the KeySpecifier is an NCName or StringLiteral , the UnaryLookup operator raises a type error [err:XPTY0004].

  3. If the KeySpecifier is a ParenthesizedExpr or a VarRef , the UnaryLookup operator is equivalent to the following expression, where KS is the value of the ParenthesizedExpr or VarRef :

    for $k in data(KS)
    return .($k)
  4. If the KeySpecifier is a wildcard (*), the UnaryLookup operator is equivalent to the following expression:

    for $k in 1 to array:size(.)
    return .($k)

    Note:

    Note that array items are returned in order.

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.

  • ?"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 4.16.1 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])

4.16.3.2 Postfix Lookup Expressions
[166]    LookupExpr    ::=    PostfixExpr Lookup
[167]    Lookup    ::=    "?" KeySpecifier
[168]    KeySpecifier    ::=    NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | "*"

The semantics of a Postfix Lookup expression depend on the form of the KeySpecifier, as follows:

  • If the KeySpecifier is an NCName, StringLiteral, VarRef, IntegerLiteral, or Wildcard (*), then the expression E?S is equivalent to E!?S. (That is, the semantics of the postfix lookup operator are defined in terms of the unary lookup operator).

  • If the KeySpecifier is a ParenthesizedExpr, then the expression E?(S) is equivalent to

    for $e in E, $s in data(S) return $e($s)

    Note:

    The focus for evaluating S is the same as the focus for the Lookup expression itself.

Examples:

  • map { "first" : "Jenna", "last" : "Scott" }?first evaluates to "Jenna"

  • map { "first name" : "Jenna", "last name" : "Scott" }?"first name" evaluates to "Jenna"

  • [4, 5, 6]?2 evaluates to 5.

  • (map {"first": "Tom"}, map {"first": "Dick"}, map {"first": "Harry"})?first evaluates to the sequence ("Tom", "Dick", "Harry").

  • ([1,2,3], [4,5,6])?2 evaluates to the sequence (2, 5).

  • ["a","b"]?3 raises a dynamic error [err:FOAY0001]FO31

4.16.3.3 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 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 test (see 3.6.4.3 Record Test), 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 test (see 3.6.4.3 Record Test), 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 IntegerLiteral 0 (zero).

Note:

Other errors, such as using an NCName KeySpecifier for an array lookup, are handled under the general provisions for type errors.

4.17 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.

[57]    FLWORExpr    ::=    InitialClause IntermediateClause* ReturnClause
[58]    InitialClause    ::=    ForClause | ForMemberClause | LetClause | WindowClause
[59]    IntermediateClause    ::=    InitialClause | WhereClause | GroupByClause | OrderByClause | CountClause
[60]    ForClause    ::=    "for" ForBinding ("," ForBinding)*
[61]    ForBinding    ::=    "$" VarName TypeDeclaration? AllowingEmpty? PositionalVar? "in" ExprSingle
[66]    LetClause    ::=    "let" LetBinding ("," LetBinding)*
[67]    LetBinding    ::=    "$" VarName TypeDeclaration? ":=" ExprSingle
[229]    TypeDeclaration    ::=    "as" SequenceType
[62]    AllowingEmpty    ::=    "allowing" "empty"
[65]    PositionalVar    ::=    "at" "$" VarName
[68]    WindowClause    ::=    "for" (TumblingWindowClause | SlidingWindowClause)
[69]    TumblingWindowClause    ::=    "tumbling" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition?
[70]    SlidingWindowClause    ::=    "sliding" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition
[71]    WindowStartCondition    ::=    "start" WindowVars ("when" ExprSingle)?
[72]    WindowEndCondition    ::=    "only"? "end" WindowVars ("when" ExprSingle)?
[73]    WindowVars    ::=    ("$" CurrentItem)? PositionalVar? ("previous" "$" PreviousItem)? ("next" "$" NextItem)?
[74]    CurrentItem    ::=    EQName
[75]    PreviousItem    ::=    EQName
[76]    NextItem    ::=    EQName
[77]    CountClause    ::=    "count" "$" VarName
[78]    WhereClause    ::=    "where" ExprSingle
[79]    GroupByClause    ::=    "group" "by" GroupingSpecList
[80]    GroupingSpecList    ::=    GroupingSpec ("," GroupingSpec)*
[81]    GroupingSpec    ::=    GroupingVariable (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
[82]    GroupingVariable    ::=    "$" VarName
[83]    OrderByClause    ::=    (("order" "by") | ("stable" "order" "by")) OrderSpecList
[84]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[85]    OrderSpec    ::=    ExprSingle OrderModifier
[86]    OrderModifier    ::=    ("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?
[87]    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.

4.17.1 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 4.17.7 Group By Clause, the binding of variables in window clauses is discussed in 4.17.4 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 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.

  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 3.4 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 or an array. 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.

4.17.2 For Clause

[60]    ForClause    ::=    "for" ForBinding ("," ForBinding)*
[63]    ForMemberClause    ::=    "for" "member" ForMemberBinding ("," ForMemberBinding)*
[61]    ForBinding    ::=    "$" VarName TypeDeclaration? AllowingEmpty? PositionalVar? "in" ExprSingle
[64]    ForMemberBinding    ::=    "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle
[229]    TypeDeclaration    ::=    "as" SequenceType
[62]    AllowingEmpty    ::=    "allowing" "empty"
[65]    PositionalVar    ::=    "at" "$" VarName

A for clause is used for iteration. Each variable in a for clause iterates over a sequence or array and is bound in turn to each item in the sequence, or to each member in the array.

If a for clause contains multiple variables, it is semantically equivalent to multiple for clauses, each containing one of the variables 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

Without the member keyword, the expression iterates over the items in a sequence. With the member keyword, it iterates over the members of an array. We refer to the sequence or array generically as the binding collection, and to its items or members as the components of the collection.

If member is specified, then the corresponding ExprSingle must evaluate to a single array, otherwise a type error is raised [err:XPTY0141].

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 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. If ordering mode is ordered, the order of tuples in the tuple stream preserves the order of the binding collection; otherwise the order of the tuple stream is implementation-dependent.

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. 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 member $x allowing empty in []

    Output tuple stream:

    ($x = ())

[Definition: A positional variable is a variable that is preceded by the keyword at.] A positional variable may be associated with a variable that is bound in a for clause. In this case, as the main variable iterates 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 always 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), the result depends on whether allowing empty is specified. If allowing empty is specified, the input tuple generates one output tuple, with the original variable bindings plus a binding of the new variable to an empty sequence. If allowing empty is not specified, the input tuple generates zero output tuples (it is not represented in the output tuple stream.)

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.

If ordering mode is ordered, 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 (assuming ordering mode is ordered):

    ($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 (assuming ordering mode is ordered):

    ($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 (assuming ordering mode is ordered):

    ($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 (assuming ordering mode is ordered):

    ($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 (assuming ordering mode is ordered):

    ($x = 1, $y = 1)
    ($x = 1, $y = 2)
    ($x = 1, $y = 3)
    ($x = 2, $y = 2)
    ($x = 2, $y = 3)
    ($x = 3, $y = 3)

In the above examples, if ordering mode had been unordered, the output tuple streams would have consisted of the same tuples, with the same values for the positional variables, but the ordering of the tuples would have been implementation-dependent.

A for clause may contain one or more type declarations, identified by the keyword as. The semantics of type declarations are defined in 4.17.1 Variable Bindings.

4.17.3 Let Clause

[66]    LetClause    ::=    "let" LetBinding ("," LetBinding)*
[67]    LetBinding    ::=    "$" VarName TypeDeclaration? ":=" ExprSingle
[229]    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 4.17.1 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]

4.17.4 Window Clause

[68]    WindowClause    ::=    "for" (TumblingWindowClause | SlidingWindowClause)
[69]    TumblingWindowClause    ::=    "tumbling" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition?
[70]    SlidingWindowClause    ::=    "sliding" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition
[71]    WindowStartCondition    ::=    "start" WindowVars ("when" ExprSingle)?
[72]    WindowEndCondition    ::=    "only"? "end" WindowVars ("when" ExprSingle)?
[73]    WindowVars    ::=    ("$" CurrentItem)? PositionalVar? ("previous" "$" PreviousItem)? ("next" "$" NextItem)?
[74]    CurrentItem    ::=    EQName
[65]    PositionalVar    ::=    "at" "$" VarName
[75]    PreviousItem    ::=    EQName
[76]    NextItem    ::=    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 4.17.4.1 Tumbling Windows and 4.17.4.2 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 4.17.4.1 Tumbling Windows and 4.17.4.2 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.

4.17.4.1 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>
4.17.4.2 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>
4.17.4.3 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 4.17.4 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. If ordering mode is ordered, the order of tuples in the tuple stream is the order in which their start items appear in the binding sequence; otherwise the order of the tuple stream is implementation-dependent. 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. If ordering mode is ordered, 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. If ordering mode is unordered, the order of tuples in the output stream is implementation-dependent.

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 4.17.7 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>

4.17.5 Where Clause

[78]    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 $inputvalues
    where $i mod 100 = 0
    return $x

4.17.6 Count Clause

[77]    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.

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
    where $rank <= 3
    return
       <product rank="{$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>

4.17.7 Group By Clause

[79]    GroupByClause    ::=    "group" "by" GroupingSpecList
[80]    GroupingSpecList    ::=    GroupingSpec ("," GroupingSpec)*
[81]    GroupingSpec    ::=    GroupingVariable (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
[82]    GroupingVariable    ::=    "$" VarName

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.] If these values are of different numeric types, and differ from each other by small amounts, then the deep-equal relationship is not transitive, because of rounding effects occurring during type promotion. When comparing three values A, B, and C such that A eq B, B eq C, but A ne C, then the number of items in the result of the function (as well as the choice of which items are returned) is implementation-dependent, subject only to the constraints that (a) no two items in the result sequence compare equal to each other, and (b) every input item that does not appear in the result sequence compares equal to some item that does appear in the result sequence. See Section 14.2.1 fn:distinct-values FO31 for further discussion of this issue in a different context.

    Note:

    The atomized grouping key will always be either an empty sequence or a single atomic value. 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 values 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 equivalent grouping 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. If ordering mode is ordered, the values derived from individual tuples are concatenated in a way that preserves the order of the pre-grouping tuple stream; otherwise the ordering of these values is implementation-dependent.

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,
        $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,
             $p in $products[itemno = $s2/itemno]
         let $category := $p/category,
             $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>

4.17.8 Order By Clause

[83]    OrderByClause    ::=    (("order" "by") | ("stable" "order" "by")) OrderSpecList
[84]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[85]    OrderSpec    ::=    ExprSingle OrderModifier
[86]    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 value nor an empty sequence, a type error is raised [err:XPTY0004].

  • If the value of an orderspec has the dynamic type xs:untypedAtomic (such as character data in a schemaless document), it is cast to the type xs:string.

    Note:

    Consistently treating untyped values as strings enables the sorting process to begin without complete knowledge of the types of all the values to be sorted.

  • If the resulting sequence contains values that are instances of more than one primitive type (meaning the 19 primitive types defined in Section 3.2 Primitive datatypesXS2, then:

    1. If each value is an instance of one of the types xs:string or xs:anyURI, then all values are cast to type xs:string.

    2. If each value is an instance of one of the types xs:decimal or xs:float, then all values are cast to type xs:float.

    3. If each value is an instance of one of the types xs:decimal, xs:float, or xs:double, then all values 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.

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 W greater-than V is true.

    2. If V is NaN and W is neither NaN nor an empty sequence, then W greater-than V is true.

    3. If a specific collation C is specified, and V and W are both of type xs:string or are convertible to xs:string by subtype substitution and/or type promotion, then:

      If fn:compare(V, W, C) is less than zero, then W greater-than V is true; otherwise W greater-than V is false.

    4. If none of the above rules apply, then:

      If W gt V is true, then W greater-than V is true; otherwise W greater-than V 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 W greater-than V is true.

    2. If W is NaN and V is neither NaN nor an empty sequence, then W greater-than V is true.

    3. If a specific collation C is specified, and V and W are both of type xs:string or are convertible to xs:string by subtype substitution and/or type promotion, then:

      If fn:compare(V, W, C) is less than zero, then W greater-than V is true; otherwise W greater-than V is false.

    4. If none of the above rules apply, then:

      If W gt V is true, then W greater-than V is true; otherwise W greater-than V 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-than V2: 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-than V1: 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:

An alternative way of sorting is available from XQuery 3.1 using the fn:sort function. In previous versions of the language, a set of books might be sorted into alphabetic order by title using the FLWOR expression:

for $b in $books/book[price < 100]
order by $b/title
return $b

In XQuery 3.1 the same effect can be achieved using the expression:

sort(
  $books/book[price < 100],
  function($book){ $book/title }
)

4.17.9 Return Clause

[87]    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 and by ordering mode. 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. If ordering mode is ordered, subsequences of assignment elements with equal deptno values will be ordered by the document order of their name elements within the emps.xml document; otherwise the ordering of these subsequences will be implementation-dependent.

  • 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,
        $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,
        $j := 20 * $i
    return ($i, $j)

4.18 Ordered and Unordered Expressions

[178]    OrderedExpr    ::=    "ordered" EnclosedExpr
[179]    UnorderedExpr    ::=    "unordered" EnclosedExpr
[42]    EnclosedExpr    ::=    "{" Expr? "}"

The purpose of ordered and unordered expressions is to set the ordering mode in the static context to ordered or unordered for the content expression. For expressions where the ordering of the result is not significant, a performance advantage may be realized by setting the ordering mode to unordered, thereby granting the system flexibility to return the result in the order that it finds most efficient.

Ordering mode affects the behavior of path expressions that include a / or // operator or an axis step; union, intersect, and except expressions; the fn:id, fn:element-with-id, and fn:idref functions; and certain clauses within a FLWOR expression. If ordering mode is ordered, node sequences returned by path expressions, union, intersect, and except expressions, and the fn:id and fn:idref functions are in document order; otherwise the order of these return sequences is implementation-dependent. The effect of ordering mode on FLWOR expressions is described in 4.17.2 For Clause, 4.17.4.3 Effects of Window Clauses on the Tuple Stream, and 4.17.7 Group By Clause. Ordering mode has no effect on duplicate elimination.

Note:

In a region of a query where ordering mode is unordered, the result of an expression is implementation-dependent if the expression calls certain functions that are affected by the ordering of node sequences. These functions include fn:position, fn:last, fn:index-of, fn:insert-before, fn:remove, fn:reverse, and fn:subsequence. The functions fn:boolean and fn:not are implementation-dependent if ordering mode is unordered and the argument contains at least one node and at least one atomic value (see 2.5.3 Effective Boolean Value). Also, within a path expression in an unordered region, numeric predicates are implementation-dependent. For example, in an ordered region, the path expression (//a/b)[5] will return the fifth qualifying b-element in document order. In an unordered region, the same expression will return an implementation-dependent qualifying b-element.

Note:

The fn:id and fn:idref functions are described in [XQuery and XPath Functions and Operators 4.0] as returning their results in document order. Since ordering mode is a feature of XQuery, relaxation of the ordering requirement for function results when ordering mode is unordered is a feature of XQuery rather than of the functions themselves.

The use of an unordered expression is illustrated by the following example, which joins together two documents named parts.xml and suppliers.xml. The example returns the part numbers of red parts, paired with the supplier numbers of suppliers who supply these parts. If an unordered expression were not used, the resulting list of (part number, supplier number) pairs would be required to have an ordering that is controlled primarily by the document order of parts.xml and secondarily by the document order of suppliers.xml. However, this might not be the most efficient way to process the query if the ordering of the result is not important. An XQuery implementation might be able to process the query more efficiently by using an index to find the red parts, or by using suppliers.xml rather than parts.xml to control the primary ordering of the result. The unordered expression gives the query evaluator freedom to make these kinds of optimizations.

unordered {
  for $p in doc("parts.xml")/parts/part[color = "Red"],
      $s in doc("suppliers.xml")/suppliers/supplier
  where $p/suppno = $s/suppno
  return
    <ps>
       { $p/partno, $s/suppno }
    </ps>
}

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 an unordered expression sets the ordering mode for its operand expression and all nested expressions.

4.19 Conditional Expressions

XQuery 4.0 and XPath 4.0 allows conditional expressions to be written in several different ways.

[101]    IfExpr    ::=    "if" "(" Expr ")" (UnbracedActions | BracedActions)
[102]    UnbracedActions    ::=    "then" ExprSingle "else" ExprSingle
[103]    BracedActions    ::=    ThenAction ElseIfAction* ElseAction?
[104]    ThenAction    ::=    EnclosedExpr
[105]    ElseIfAction    ::=    "else" "if" "(" Expr ")" EnclosedExpr
[106]    ElseAction    ::=    "else" EnclosedExpr
[42]    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.

4.20 Otherwise Expression

[119]    OtherwiseExpr    ::=    UnionExpr ( "otherwise" UnionExpr )*

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.

Editorial note 2022-12-20
This change was approved during QT4CG meeting 016 on 20 December, 2022

4.21 Switch Expression

[90]    SwitchExpr    ::=    "switch" SwitchComparand? (SwitchCases | BracedSwitchCases)
[91]    SwitchComparand    ::=    "(" Expr ")"
[92]    SwitchCases    ::=    SwitchCaseClause+ "default" "return" ExprSingle
[93]    BracedSwitchCases    ::=    "{" SwitchCases "}"
[94]    SwitchCaseClause    ::=    ("case" SwitchCaseOperand)+ "return" ExprSingle
[95]    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 values 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 braces 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.

4.22 Quantified Expressions

Quantified expressions support existential and universal quantification. The value of a quantified expression is always true or false.

[88]    QuantifiedExpr    ::=    ("some" | "every") QuantifierBinding ("," QuantifierBinding)* "satisfies" ExprSingle
[89]    QuantifierBinding    ::=    "$" VarName TypeDeclaration? "in" ExprSingle
[229]    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 value true; 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 value true; 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 bound in an in-clause of a quantified expression may have an optional type declaration. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is raised [err:XPTY0004].

The order in which test expressions are evaluated for the various binding tuples is implementation-dependent. If the quantifier is some, an implementation may return true as soon as it finds one binding tuple 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 binding tuple 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 binding tuple 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 binding tuple 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 and XPath 4.0 is to use the higher-order functions fn:some and fn:every. This example can be written fn:every(/emps/employee, function{salary/@current='true'})

  • In the following examples, each quantified expression evaluates its test expression over nine pairs of variable bindings, 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 variable binding 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 variable binding and raises a type error for another:

    every $x in (1, 2, "cat") satisfies $x * 2 = 4
  • This quantified expression contains a type declaration that is not satisfied by every item in the test expression. If the Static Typing Feature is implemented, this expression raises a type error during the static analysis phase. Otherwise, the expression may either return true or raise a type error during the dynamic evaluation phase.

    some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4

4.23 Try/Catch Expressions

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.

[107]    TryCatchExpr    ::=    TryClause CatchClause+
[108]    TryClause    ::=    "try" EnclosedTryTargetExpr
[109]    EnclosedTryTargetExpr    ::=    EnclosedExpr
[110]    CatchClause    ::=    "catch" NameTestUnion EnclosedExpr
[111]    NameTestUnion    ::=    NameTest ("|" NameTest)*
[154]    NameTest    ::=    EQName | Wildcard
[42]    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:

Variable Type Value
$err:code xs:QName The error code
$err:description xs: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:value item()* 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:module xs: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-number xs: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-number xs: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:additional item()* Implementation-defined. This variable must be bound so that a query can reference it without raising an error. The purpose of this variable is to allow implementations to provide any additional information that might be useful.
$err:map map(*) 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 a CatchErrorList catches any error:

    try {
      $x cast as xs:integer
    } catch * {
      0
    }
  • The CatchErrorList in this try/catch expression specifies that only err:FORG0001 is caught:

    try {
      $x cast as xs:integer
    } catch err:FORG0001 {
      0
    }
  • The CatchErrorList in 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. Since the CatchErrorList is a wildcard, it catches any error:

    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, map { 'method': 'adaptive' })
    }

4.24 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.

4.24.1 Instance Of

[122]    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 absentDM31, a dynamic 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 4.24.4 Castable

4.24.2 Typeswitch

[96]    TypeswitchExpr    ::=    "typeswitch" "(" Expr ")" (TypeswitchCases | BracedTypeswitchCases)
[97]    TypeswitchCases    ::=    CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[98]    BracedTypeswitchCases    ::=    "{" TypeswitchCases "}"
[99]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceTypeUnion "return" ExprSingle
[100]    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 braces 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(*, AustraliaAddress)
            | element(*, MexicoAddress)
     return $a/state
   case $a as element(*, CanadaAddress)
     return $a/province
   case $a as element(*, JapanAddress)
     return $a/prefecture
   default
     return "unknown"
}

4.24.3 Cast

[125]    CastExpr    ::=    ArrowExpr ( "cast" "as" SingleType )?
[228]    SingleType    ::=    CastTarget "?"?
[251]    TypeName    ::=    EQName
[265]    LocalUnionType    ::=    "union" "(" ItemType ("," ItemType)* ")"
[266]    EnumerationType    ::=    "enum" "(" StringLiteral ("," StringLiteral)* ")"

Sometimes it is necessary to convert a value to a specific datatype. For this purpose, XQuery 4.0 and XPath 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 one of:

  • The name of an item type alias 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 [err:XQST0052]. In addition, the target type cannot be xs:NOTATION, xs:anySimpleType, or xs:anyAtomicType

  • A LocalUnionType such as union(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 value, 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 value, the result of the cast expression is determined by casting to the target type as described in Section 19 Casting FO31. 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 union(enum("red"), enum("green")).

4.24.4 Castable

[124]    CastableExpr    ::=    CastExpr ( "castable" "as" SingleType )?
[228]    SingleType    ::=    CastTarget "?"?
[251]    TypeName    ::=    EQName
[265]    LocalUnionType    ::=    "union" "(" ItemType ("," ItemType)* ")"
[266]    EnumerationType    ::=    "enum" "(" StringLiteral ("," StringLiteral)* ")"

XQuery 4.0 and XPath 4.0 provides an expression that tests whether a given value is castable into a given target type. The target type must be one of:

  • The name of an item type alias 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 [err:XQST0052]. In addition, the target type cannot be xs:NOTATION, xs:anySimpleType, or xs:anyAtomicType

  • A LocalUnionType such as union(xs:date, xs:dateTime).

  • An EnumerationType such as enum("red", "green", "blue").

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.

4.24.5 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 18 Constructor functions FO31. There is also a constructor function for every named item type in the item type aliases that maps to a generalized atomic type.

All such constructor functions are classified as system functions.

[Definition: The constructor function for a given 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 defined as a type alias for union(xs:date, xs:time, xs:dateTime), then the result of my:chrono("12:00:00Z") is the xs:time value 12:00:00Z.

Note:

An instance of an atomic type that is not in a 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.

4.24.6 Treat

[123]    TreatExpr    ::=    CastableExpr ( "treat" "as" SequenceType )?

XQuery 4.0 and XPath 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].

4.25 Simple map operator (!)

[140]    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 values, 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. These sequences are concatenated and returned. If ordering mode is ordered, the The returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2 . ; otherwise the order of the returned sequence is implementation-dependent.

Simple map operators have functionality similar to 4.7.3 Path operator (/). The following table summarizes the differences between these two operators

Operator Path operator (E1 / E2) Simple map operator (E1 ! E2)
E1 Any sequence of nodes Any sequence of items
E2 Either a sequence of nodes or a sequence of non-node items A sequence of items
Additional processing Duplicate elimination and document ordering Simple 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 value.)

  • 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.

4.26 Arrow Expressions

[126]    ArrowExpr    ::=    UnaryExpr ( (SequenceArrowTarget | MappingArrowTarget) )*
[129]    SequenceArrowTarget    ::=    "=>" ArrowTarget
[130]    MappingArrowTarget    ::=    "=!>" ArrowTarget
[131]    ArrowTarget    ::=    (ArrowStaticFunction ArgumentList) | (ArrowDynamicFunction PositionalArgumentList)
[169]    ArrowStaticFunction    ::=    EQName
[170]    ArrowDynamicFunction    ::=    VarRef | InlineFunctionExpr | ParenthesizedExpr
[212]    InlineFunctionExpr    ::=    Annotation* ("function" | "fn") FunctionSignature? FunctionBody
[159]    ArgumentList    ::=    "(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
[160]    PositionalArgumentList    ::=    "(" PositionalArguments? ")"

[Definition: The arrow operator applies a function to the value of an expression, using the value as the first argument to the function.]

The sequence arrow operator => is defined as follows:

[Definition: The mapping arrow operator =!> applies a function to each item in a sequence.] It is defined as follows:

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.

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+")

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()

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()).

4.27 Validate Expressions

[135]    ValidateExpr    ::=    "validate" (ValidationMode | ("type" TypeName))? "{" Expr "}"
[136]    ValidationMode    ::=    "lax" | "strict"
[42]    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 as a name in 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) 3.1]. 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. 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.

  5. 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) 3.1] 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 annotation xs:anyType, and any attribute information items whose validity property is notKnown are converted into attribute nodes with type annotation xs:untypedAtomic, as described in Section 3.3.1.1 Element and Attribute Node Types DM31.

4.28 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.

[137]    ExtensionExpr    ::=    Pragma+ "{" Expr? "}"
[138]    Pragma    ::=    "(#" S? EQName (S PragmaContents)? "#)" /* ws: explicit */
[139]    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 (however, static type errors are raised only if the Static Typing Feature is in effect.)

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 braces may be omitted, in which case implementations that do not recognize the pragma will raise a static error.

5 Modules and Prologs

[2]    Module    ::=    VersionDecl? (LibraryModule | MainModule)
[4]    MainModule    ::=    Prolog QueryBody
[5]    LibraryModule    ::=    ModuleDecl Prolog
[7]    Prolog    ::=    ((DefaultNamespaceDecl | Setter | NamespaceDecl | Import) Separator)* ((ContextValueDecl | AnnotatedDecl | OptionDecl) Separator)*
[9]    Setter    ::=    BoundarySpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl | DecimalFormatDecl
[21]    Import    ::=    SchemaImport | ModuleImport
[8]    Separator    ::=    ";"
[45]    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, ordering 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

[3]    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 separated by a dot. The first integer is referred to as the major version number; the second as the minor version number.] Any XQuery processor that implements any version of XQuery with a given major number must accept any query with the same major version number. The processor may reject queries labeled with a different major version number. The processor may reject queries with the same major version number and a greater minor version number than the processor recognizes. If a query is rejected because of a version mismatch with the processor, a static error [err:XQST0031] must be raised.

Note:

The processor is allowed to provide an option to require that minor versions also match, or that the minor number of the version in the query is not larger than the largest minor version understood by the processor in this major release of XQuery, or to allow more permissive version matching, perhaps with warnings, but the behaviour is then outside the scope of this specification.

The version number “1.0” indicates the intent that the module be processed by an XQuery 1.0 processor, the version number “3.0” indicates the intent that the module be processed by an XQuery 3.0 processor, the version number “3.1” indicates the intent that the module be processed by an XQuery 3.1 processor. If the version declaration is not present or the version is not included in the declaration, an XQuery 3.1 processor assumes a version of “3.1”.

[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 "1.0";
xquery version "3.0" encoding "utf-8";

5.2 Module Declaration

[6]    ModuleDecl    ::=    "module" "namespace" NCName "=" URILiteral Separator

[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

[10]    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 4.13.1.4 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

[11]    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

[12]    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 absentDM31 [err:XPST0001]. When the Static Base URI property is absentDM31, any attempt to use its value to resolve a relative URI reference will result in an error [err:XPST0001].

5.6 Construction Declaration

[13]    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

[14]    OrderingModeDecl    ::=    "declare" "ordering" ("ordered" | "unordered")

[Definition: An ordering mode declaration sets the ordering mode in the static context, overriding any implementation-defined default.] This ordering mode applies to all expressions in a module (including both the Prolog and the Query Body, if any), unless overridden by an ordered or unordered expression.

The following example illustrates an ordering mode declaration:

declare ordering unordered;

If a Prolog contains more than one ordering mode declaration, a static error is raised [err:XQST0065].

5.8 Empty Order Declaration

[15]    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].

Note:

It is important to distinguish an empty order declaration from an ordering mode declaration. An empty order declaration applies only when an order by clause is present, and specifies how empty sequences are treated by the order by clause (unless overridden). An ordering mode declaration, on the other hand, applies only in the absence of an order by clause.

5.9 Copy-Namespaces Declaration

[16]    CopyNamespacesDecl    ::=    "declare" "copy-namespaces" PreserveMode "," InheritMode
[17]    PreserveMode    ::=    "preserve" | "no-preserve"
[18]    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 4.13.1 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

[19]    DecimalFormatDecl    ::=    "declare" (("decimal-format" EQName) | ("default" "decimal-format")) (DFPropertyName "=" StringLiteral)*
[20]    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

[22]    SchemaImport    ::=    "import" "schema" SchemaPrefix? URILiteral ("at" URILiteral ("," URILiteral)*)?
[23]    SchemaPrefix    ::=    ("namespace" NCName "=") | ("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].

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.

The first URILiteral in a schema import specifies the target namespace of the schema to be imported. The URILiterals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an implementation-dependent way. Multiple location hints might be used to indicate more than one possible place to look for the schema or multiple physical resources to be assembled to form the schema.

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.

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 element and/or type namespace 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 .

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:XQST0035] if multiple imported schemas, or multiple physical resources within one schema, contain definitions for the same name in the same symbol space (for example, two definitions for the same element name, even if the definitions are consistent). However, it is not an error to import the schema with target namespace http://www.w3.org/2001/XMLSchema (predeclared prefix xs), even though the built-in types defined in this schema are implicitly included in the in-scope schema types.

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--i.e., each definition must be valid, complete, and unique.

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

[24]    ModuleImport    ::=    "import" "module" ("namespace" NCName "=")? URILiteral ("at" URILiteral ("," 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 item type aliases 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 in-scope schema definitions and statically known function definitions of module B, and the dynamic context of module A will contain the variable values and dynamically known function definitions of module B, with the exception of non-public functions and variables, and of the functions and variables not declared directly in B.

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].

Each module has its own static context. A module import imports only functions, variable declarations, and item type declaratons; it does not import other objects from the imported modules, such as in-scope schema definitions or statically known namespaces. Module imports are not transitive—that is, 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 $t as geometry:triangle := geo:make-triangle(); 
$t

Without the type declaration for the variable, the variable declaration succeeds:

import module namespace geo = "http://example.org/geo-functions";
declare variable $t := geo:make-triangle(); $t

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 $t as geometry:triangle := geo:make-triangle(); $t

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 module contexts of a query: that is, 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

[25]    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 that are present in the statically known namespaces before each query is processed. These prefixes may be used without an explicit declaration. 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]). The predeclared namespace prefixes are as follows:

  • 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

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

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

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

  • err = http://www.w3.org/2005/xqt-errors

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

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 $i := <foo:bar xmlns:foo = "http://example.org">
              <foo:bing> Lentils </foo:bing>
          </foo:bar>
return $i/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

[26]    DefaultNamespaceDecl    ::=    "declare" "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 absentDM31.

    The following example illustrates the declaration of a default namespace for elements:

    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.)

  • 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 absentDM31). 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.

Unprefixed attribute names and variable names are in no namespace.

5.15 Annotations

[27]    AnnotatedDecl    ::=    "declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl)
[212]    InlineFunctionExpr    ::=    Annotation* ("function" | "fn") FunctionSignature? FunctionBody
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[29]    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.

Implementations may define further annotations, whose behaviour is implementation-defined. For instance, if the eg prefix is bound to a namespace associated with a particular implementation, it could define an annotation like eg:sequential. If the namespace URI of an annotation is not recognized by the implementation, then the annotation is ignored. Implementations may also provide a way for users to define their own annotations. Implementations must not define annotations in reserved namespaces; it is a static error [err:XQST0045] for a user to define an annotation 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.

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

[27]    AnnotatedDecl    ::=    "declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl)
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[30]    VarDecl    ::=    "variable" "$" VarName TypeDeclaration? ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
[175]    VarName    ::=    EQName
[229]    TypeDeclaration    ::=    "as" SequenceType
[31]    VarValue    ::=    ExprSingle
[32]    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

  • If the Static Typing Feature is in effect and VarValue is present, then the static type inferred from static analysis of the expression VarValue;

    Note:

    Type inference might not be computable until after the check for circular dependencies, described below, is complete.

  • 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, other than the variable being declared.]

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 $a depends 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

[33]    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

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.

[27]    AnnotatedDecl    ::=    "declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl)
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[34]    FunctionDecl    ::=    "function" EQName FunctionSignatureWithDefaults (FunctionBody | "external") /* xgc: reserved-function-names */
[35]    FunctionSignatureWithDefaults    ::=    "(" ParamListWithDefaults? ")" TypeDeclaration?
[37]    ParamListWithDefaults    ::=    ParamWithDefault ("," ParamWithDefault)*
[38]    ParamWithDefault    ::=    "$" EQName TypeDeclaration? (":=" ExprSingle)?
[41]    FunctionBody    ::=    EnclosedExpr
[229]    TypeDeclaration    ::=    "as" SequenceType
[42]    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 and XPath 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 $d in fn:distinct-values($emps/deptno) 
   let $e := $emps[deptno = $d]
   return 
      <dept> 
          <deptno>{$d}</deptno> 
          <headcount> {fn:count($e)} </headcount> 
          <payroll> {fn:sum($e/salary)} </payroll> 
      </dept> 
};
          
local:summary(fn: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. However, its context value static type component is absentDM31, and an implementation should raise a static error [err:XPST0008] if an expression depends on the context value.

The properties of the function definition F 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/math

  • http://www.w3.org/2012/xquery

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

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

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 4.6.1.2 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. 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(*) := 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 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

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) 3.1] 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 (fn:empty($e/*)) 
   then 1
   else fn: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 definition in full.

[27]    AnnotatedDecl    ::=    "declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl)
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[43]    ItemTypeDecl    ::=    "item-type" EQName "as" ItemType

An item-type declaration adds a named item type to the item type aliases of the containing module. This enables the item type to be referred to using a simple name.

For example, given the declaration:

declare item-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 item-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 no namespace.

All item type names declared in a library module must (when expanded) be in the target namespace of the library module [err:XQST0048].

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. [Definition: 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 item type aliases of another module. ] [Definition: 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 item type aliases 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 an item type declaration contains both a %private and a %public annotation, more than one %private annotation, or more than one %public annotation.

It is a static error if two item type declarations (whether locally declared in a module or imported from a public declaration in an imported module) share the same name [err:XQST0146]

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.

5.20 Option Declaration

[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.]

[44]    OptionDecl    ::=    "declare" "option" EQName StringLiteral

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";

6 Conformance

This section defines the conformance criteria for an XQuery 4.0 and XPath 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.]

XPath is intended primarily as a component that can be used by other specifications. Therefore, XPath relies on specifications that use it (such as [XPointer] and [XSL Transformations (XSLT) Version 3.0]) to specify conformance criteria for XPath in their respective environments. Specifications that set conformance criteria for their use of XPath MUST NOT change the syntactic or semantic definitions of XPath as given in this specification, except by subsetting and/or compatible extensions.

If a language is described as an extension of XPath, then every expression that conforms to the XPath grammar MUST behave as described in this specification.

An XQuery processor that claims to conform to this specification MUST include a claim of Minimal Conformance as defined in 6.2 Minimal Conformance. In addition to a claim of Minimal Conformance, it MAY claim conformance to one or more optional features defined in 6.3 Optional Features.

6.1 Static Typing Feature

[Definition: The Static Typing Feature is an optional feature of XPath that provides support for static semantics, and requires implementations to detect and report type errors during the static analysis phase.] Specifications that use XPath MAY specify conformance criteria for use of the Static Typing Feature.

If an implementation does not support the Static Typing Feature, but can nevertheless determine during the static analysis phase that a QueryBody an XPath expression, if evaluated, would necessarily raise a dynamic error or that an expression, if evaluated, would necessarily raise a type error, the implementation MAY raise that error during the static analysis phase. The choice of whether to raise such an error at analysis time is implementation dependent.

6.2 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 6.3 Optional Features to be optional. If an implementation does not provide a given optional feature, it MUST implement any requirements specified in 6.3 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 E 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) 3.1], as specified in 6.4 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.

6.3 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.

6.3.1 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 4.27 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 6.3.2 Typed Data Feature.

6.3.2 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.)

6.3.3 Static Typing Feature

[Definition: The Static Typing Feature requires implementations to report all type errors during the static analysis phase.]

If an implementation provides the Static Typing Feature, then it MUST raise an error during static analysis whenever the inferred static type of an expression is not subsumed by the required type for the context in which it appears.

If an implementation does not provide the Static Typing Feature, then it MUST NOT report type errors during the static analysis phase except in cases where the inferred static type and the required type have an empty intersection (that is, where evaluation of the expression is guaranteed to fail). It MAY defer some or all type checking until the dynamic evaluation phase.

6.3.4 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.

6.3.5 Serialization Feature

[Definition: The Serialization Feature provides means for serializing the result of a query as specified in 2.3.4 Serialization.] A conforming XQuery implementation that provides the Serialization Feature MUST conform to 2.3.4 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 3.1], 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 14.7.3 fn:serialize FO31. 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.

6.4 Data Model Conformance

All XQuery implementations process data represented in the data model as specified in [XQuery and XPath Data Model (XDM) 3.1]. 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 Infoset DM31, 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 PSVI DM31, 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) 3.1], 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.

6.5 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 and XPath 4.0 Grammar

A.1 EBNF

The grammar of XQuery 4.0 and XPath 4.0 uses the same simple Extended Backus-Naur Form (EBNF) notation as [XML 1.0] with the following minor differences.

  • 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.

[1]    XPath    ::=    Expr
[2]    Module    ::=    VersionDecl? (LibraryModule | MainModule)
[3]    VersionDecl    ::=    "xquery" (("encoding" StringLiteral) | ("version" StringLiteral ("encoding" StringLiteral)?)) Separator
[4]    MainModule    ::=    Prolog QueryBody
[5]    LibraryModule    ::=    ModuleDecl Prolog
[6]    ModuleDecl    ::=    "module" "namespace" NCName "=" URILiteral Separator
[7]    Prolog    ::=    ((DefaultNamespaceDecl | Setter | NamespaceDecl | Import) Separator)* ((ContextValueDecl | AnnotatedDecl | OptionDecl) Separator)*
[8]    Separator    ::=    ";"
[9]    Setter    ::=    BoundarySpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderDecl | CopyNamespacesDecl | DecimalFormatDecl
[10]    BoundarySpaceDecl    ::=    "declare" "boundary-space" ("preserve" | "strip")
[11]    DefaultCollationDecl    ::=    "declare" "default" "collation" URILiteral
[12]    BaseURIDecl    ::=    "declare" "base-uri" URILiteral
[13]    ConstructionDecl    ::=    "declare" "construction" ("strip" | "preserve")
[14]    OrderingModeDecl    ::=    "declare" "ordering" ("ordered" | "unordered")
[15]    EmptyOrderDecl    ::=    "declare" "default" "order" "empty" ("greatest" | "least")
[16]    CopyNamespacesDecl    ::=    "declare" "copy-namespaces" PreserveMode "," InheritMode
[17]    PreserveMode    ::=    "preserve" | "no-preserve"
[18]    InheritMode    ::=    "inherit" | "no-inherit"
[19]    DecimalFormatDecl    ::=    "declare" (("decimal-format" EQName) | ("default" "decimal-format")) (DFPropertyName "=" StringLiteral)*
[20]    DFPropertyName    ::=    "decimal-separator" | "grouping-separator" | "infinity" | "minus-sign" | "NaN" | "percent" | "per-mille" | "zero-digit" | "digit" | "pattern-separator" | "exponent-separator"
[21]    Import    ::=    SchemaImport | ModuleImport
[22]    SchemaImport    ::=    "import" "schema" SchemaPrefix? URILiteral ("at" URILiteral ("," URILiteral)*)?
[23]    SchemaPrefix    ::=    ("namespace" NCName "=") | ("default" "element" "namespace")
[24]    ModuleImport    ::=    "import" "module" ("namespace" NCName "=")? URILiteral ("at" URILiteral ("," URILiteral)*)?
[25]    NamespaceDecl    ::=    "declare" "namespace" NCName "=" URILiteral
[26]    DefaultNamespaceDecl    ::=    "declare" "default" ("element" | "function") "namespace" URILiteral
[27]    AnnotatedDecl    ::=    "declare" Annotation* (VarDecl | FunctionDecl | ItemTypeDecl)
[28]    Annotation    ::=    "%" EQName ("(" AnnotationValue ("," AnnotationValue)* ")")?
[29]    AnnotationValue    ::=    StringLiteral | ("-"? NumericLiteral) | ("true" "(" ")") | ("false" "(" ")")
[30]    VarDecl    ::=    "variable" "$" VarName TypeDeclaration? ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
[31]    VarValue    ::=    ExprSingle
[32]    VarDefaultValue    ::=    ExprSingle
[33]    ContextValueDecl    ::=    "declare" "context" (("value" ("as" SequenceType)?) | ("item" ("as" ItemType)?)) ((":=" VarValue) | ("external" (":=" VarDefaultValue)?))
[34]    FunctionDecl    ::=    "function" EQName FunctionSignatureWithDefaults (FunctionBody | "external") /* xgc: reserved-function-names */
[35]    FunctionSignatureWithDefaults    ::=    "(" ParamListWithDefaults? ")" TypeDeclaration?
[36]    FunctionSignature    ::=    "(" ParamList? ")" TypeDeclaration?
[37]    ParamListWithDefaults    ::=    ParamWithDefault ("," ParamWithDefault)*
[38]    ParamWithDefault    ::=    "$" EQName TypeDeclaration? (":=" ExprSingle)?
[39]    ParamList    ::=    Param ("," Param)*
[40]    Param    ::=    "$" EQName TypeDeclaration?
[41]    FunctionBody    ::=    EnclosedExpr
[42]    EnclosedExpr    ::=    "{" Expr? "}"
[43]    ItemTypeDecl    ::=    "item-type" EQName "as" ItemType
[44]    OptionDecl    ::=    "declare" "option" EQName StringLiteral
[45]    QueryBody    ::=    Expr
[46]    Expr    ::=    ExprSingle ("," ExprSingle)*
[47]    ExprSingle    ::=    WithExpr
| ForExpr
| LetExpr
| FLWORExpr
| QuantifiedExpr
| SwitchExpr
| TypeswitchExpr
| IfExpr
| TryCatchExpr
| OrExpr
[48]    WithExpr    ::=    "with" NamespaceDeclaration ("," NamespaceDeclaration)* EnclosedExpr
[49]    NamespaceDeclaration    ::=    QName "=" URILiteral StringLiteral
[50]    ForExpr    ::=    SimpleForClause SimpleReturnClause
[51]    SimpleForClause    ::=    "for" SimpleForBinding (("for" | ",") SimpleForBinding)*
[52]    SimpleForBinding    ::=    "member"? "$" VarName "in" ExprSingle
[53]    SimpleReturnClause    ::=    "return" ExprSingle
[54]    LetExpr    ::=    SimpleLetClause SimpleReturnClause
[55]    SimpleLetClause    ::=    "let" SimpleLetBinding (("let" | ",") SimpleLetBinding)*
[56]    SimpleLetBinding    ::=    "$" VarName ":=" ExprSingle
[57]    FLWORExpr    ::=    InitialClause IntermediateClause* ReturnClause
[58]    InitialClause    ::=    ForClause | ForMemberClause | LetClause | WindowClause
[59]    IntermediateClause    ::=    InitialClause | WhereClause | GroupByClause | OrderByClause | CountClause
[60]    ForClause    ::=    "for" ForBinding ("," ForBinding)*
[61]    ForBinding    ::=    "$" VarName TypeDeclaration? AllowingEmpty? PositionalVar? "in" ExprSingle
[62]    AllowingEmpty    ::=    "allowing" "empty"
[63]    ForMemberClause    ::=    "for" "member" ForMemberBinding ("," ForMemberBinding)*
[64]    ForMemberBinding    ::=    "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle
[65]    PositionalVar    ::=    "at" "$" VarName
[66]    LetClause    ::=    "let" LetBinding ("," LetBinding)*
[67]    LetBinding    ::=    "$" VarName TypeDeclaration? ":=" ExprSingle
[68]    WindowClause    ::=    "for" (TumblingWindowClause | SlidingWindowClause)
[69]    TumblingWindowClause    ::=    "tumbling" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition?
[70]    SlidingWindowClause    ::=    "sliding" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition? WindowEndCondition
[71]    WindowStartCondition    ::=    "start" WindowVars ("when" ExprSingle)?
[72]    WindowEndCondition    ::=    "only"? "end" WindowVars ("when" ExprSingle)?
[73]    WindowVars    ::=    ("$" CurrentItem)? PositionalVar? ("previous" "$" PreviousItem)? ("next" "$" NextItem)?
[74]    CurrentItem    ::=    EQName
[75]    PreviousItem    ::=    EQName
[76]    NextItem    ::=    EQName
[77]    CountClause    ::=    "count" "$" VarName
[78]    WhereClause    ::=    "where" ExprSingle
[79]    GroupByClause    ::=    "group" "by" GroupingSpecList
[80]    GroupingSpecList    ::=    GroupingSpec ("," GroupingSpec)*
[81]    GroupingSpec    ::=    GroupingVariable (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
[82]    GroupingVariable    ::=    "$" VarName
[83]    OrderByClause    ::=    (("order" "by") | ("stable" "order" "by")) OrderSpecList
[84]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[85]    OrderSpec    ::=    ExprSingle OrderModifier
[86]    OrderModifier    ::=    ("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?
[87]    ReturnClause    ::=    "return" ExprSingle
[88]    QuantifiedExpr    ::=    ("some" | "every") QuantifierBinding ("," QuantifierBinding)* "satisfies" ExprSingle
[89]    QuantifierBinding    ::=    "$" VarName TypeDeclaration? "in" ExprSingle
[90]    SwitchExpr    ::=    "switch" SwitchComparand? (SwitchCases | BracedSwitchCases)
[91]    SwitchComparand    ::=    "(" Expr ")"
[92]    SwitchCases    ::=    SwitchCaseClause+ "default" "return" ExprSingle
[93]    BracedSwitchCases    ::=    "{" SwitchCases "}"
[94]    SwitchCaseClause    ::=    ("case" SwitchCaseOperand)+ "return" ExprSingle
[95]    SwitchCaseOperand    ::=    Expr
[96]    TypeswitchExpr    ::=    "typeswitch" "(" Expr ")" (TypeswitchCases | BracedTypeswitchCases)
[97]    TypeswitchCases    ::=    CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[98]    BracedTypeswitchCases    ::=    "{" TypeswitchCases "}"
[99]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceTypeUnion "return" ExprSingle
[100]    SequenceTypeUnion    ::=    SequenceType ("|" SequenceType)*
[101]    IfExpr    ::=    "if" "(" Expr ")" (UnbracedActions | BracedActions)
[102]    UnbracedActions    ::=    "then" ExprSingle "else" ExprSingle
[103]    BracedActions    ::=    ThenAction ElseIfAction* ElseAction?
[104]    ThenAction    ::=    EnclosedExpr
[105]    ElseIfAction    ::=    "else" "if" "(" Expr ")" EnclosedExpr
[106]    ElseAction    ::=    "else" EnclosedExpr
[107]    TryCatchExpr    ::=    TryClause CatchClause+
[108]    TryClause    ::=    "try" EnclosedTryTargetExpr
[109]    EnclosedTryTargetExpr    ::=    EnclosedExpr
[110]    CatchClause    ::=    "catch" NameTestUnion EnclosedExpr
[111]    NameTestUnion    ::=    NameTest ("|" NameTest)*
[112]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[113]    AndExpr    ::=    ComparisonExpr ( "and" ComparisonExpr )*
[114]    ComparisonExpr    ::=    StringConcatExpr ( (ValueComp
| GeneralComp
| NodeComp) StringConcatExpr )?
[115]    StringConcatExpr    ::=    RangeExpr ( "||" RangeExpr )*
[116]    RangeExpr    ::=    AdditiveExpr ( "to" AdditiveExpr )?
[117]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[118]    MultiplicativeExpr    ::=    OtherwiseExpr ( ("*" | "×" | "div" | "÷" | "idiv" | "mod") OtherwiseExpr )*
[119]    OtherwiseExpr    ::=    UnionExpr ( "otherwise" UnionExpr )*
[120]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[121]    IntersectExceptExpr    ::=    InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*
[122]    InstanceofExpr    ::=    TreatExpr ( "instance" "of" SequenceType )?
[123]    TreatExpr    ::=    CastableExpr ( "treat" "as" SequenceType )?
[124]    CastableExpr    ::=    CastExpr ( "castable" "as" SingleType )?
[125]    CastExpr    ::=    ArrowExpr ( "cast" "as" SingleType )?
[126]    ArrowExpr    ::=    UnaryExpr ( (SequenceArrowTarget | MappingArrowTarget) )*
[127]    UnaryExpr    ::=    ("-" | "+")* ValueExpr
[128]    ValueExpr    ::=    ValidateExpr | ExtensionExpr | SimpleMapExpr
[129]    SequenceArrowTarget    ::=    "=>" ArrowTarget
[130]    MappingArrowTarget    ::=    "=!>" ArrowTarget
[131]    ArrowTarget    ::=    (ArrowStaticFunction ArgumentList) | (ArrowDynamicFunction PositionalArgumentList)
[132]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[133]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[134]    NodeComp    ::=    "is" | "<<" | ">>"
[135]    ValidateExpr    ::=    "validate" (ValidationMode | ("type" TypeName))? "{" Expr "}"
[136]    ValidationMode    ::=    "lax" | "strict"
[137]    ExtensionExpr    ::=    Pragma+ "{" Expr? "}"
[138]    Pragma    ::=    "(#" S? EQName (S PragmaContents)? "#)" /* ws: explicit */
[139]    PragmaContents    ::=    (Char* - (Char* '#)' Char*))
[140]    SimpleMapExpr    ::=    PathExpr ("!" PathExpr)*
[141]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* xgc: leading-lone-slash */
[142]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*
[143]    StepExpr    ::=    PostfixExpr | AxisStep
[144]    AxisStep    ::=    (ReverseStep | ForwardStep) PredicateList
[145]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbrevForwardStep
[146]    ForwardAxis    ::=    ("child" "::")
| ("descendant" "::")
| ("attribute" "::")
| ("self" "::")
| ("descendant-or-self" "::")
| ("following-sibling" "::")
| ("following" "::")
| ("namespace" "::")
[147]    AbbrevForwardStep    ::=    ("@" NodeTest) | SimpleNodeTest
[148]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbrevReverseStep
[149]    ReverseAxis    ::=    ("parent" "::")
| ("ancestor" "::")
| ("preceding-sibling" "::")
| ("preceding" "::")
| ("ancestor-or-self" "::")
[150]    AbbrevReverseStep    ::=    ".."
[151]    NodeTest    ::=    UnionNodeTest | SimpleNodeTest
[152]    UnionNodeTest    ::=    "(" SimpleNodeTest ("|" SimpleNodeTest)* ")"
[153]    SimpleNodeTest    ::=    KindTest | NameTest
[154]    NameTest    ::=    EQName | Wildcard
[155]    Wildcard    ::=    "*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
[156]    FilterExpr    ::=    PostfixExpr Predicate
[157]    PostfixExpr    ::=    PrimaryExpr | FilterExpr | DynamicFunctionCall | LookupExpr
[158]    DynamicFunctionCall    ::=    PostfixExpr PositionalArgumentList
[159]    ArgumentList    ::=    "(" ((PositionalArguments ("," KeywordArguments)?) | KeywordArguments)? ")"
[160]    PositionalArgumentList    ::=    "(" PositionalArguments? ")"
[161]    PositionalArguments    ::=    Argument ("," Argument)*
[162]    KeywordArguments    ::=    KeywordArgument ("," KeywordArgument)*
[163]    KeywordArgument    ::=    EQName ":=" Argument
[164]    PredicateList    ::=    Predicate*
[165]    Predicate    ::=    "[" Expr "]"
[166]    LookupExpr    ::=    PostfixExpr Lookup
[167]    Lookup    ::=    "?" KeySpecifier
[168]    KeySpecifier    ::=    NCName | IntegerLiteral | StringLiteral | VarRef | ParenthesizedExpr | "*"
[169]    ArrowStaticFunction    ::=    EQName
[170]    ArrowDynamicFunction    ::=    VarRef | InlineFunctionExpr | ParenthesizedExpr
[171]    PrimaryExpr    ::=    Literal
| VarRef
| ParenthesizedExpr
| ContextValueExpr
| FunctionCall
| OrderedExpr
| UnorderedExpr
| NodeConstructor
| FunctionItemExpr
| MapConstructor
| ArrayConstructor
| StringTemplate
| StringConstructor
| UnaryLookup
[172]    Literal    ::=    NumericLiteral | StringLiteral
[173]    NumericLiteral    ::=    IntegerLiteral | HexIntegerLiteral | BinaryIntegerLiteral | DecimalLiteral | DoubleLiteral
[174]    VarRef    ::=    "$" VarName
[175]    VarName    ::=    EQName
[176]    ParenthesizedExpr    ::=    "(" Expr? ")"
[177]    ContextValueExpr    ::=    "."
[178]    OrderedExpr    ::=    "ordered" EnclosedExpr
[179]    UnorderedExpr    ::=    "unordered" EnclosedExpr
[180]    FunctionCall    ::=    EQName ArgumentList /* xgc: reserved-function-names */
/* gn: parens */
[181]    Argument    ::=    ExprSingle | ArgumentPlaceholder
[182]    ArgumentPlaceholder    ::=    "?"
[183]    NodeConstructor    ::=    DirectConstructor
| ComputedConstructor
[184]    DirectConstructor    ::=    DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
[185]    DirElemConstructor    ::=    "<" QName DirAttributeList ("/>" | (">" DirElemContent* "</" QName S? ">")) /* ws: explicit */
[186]    DirAttributeList    ::=    (S (QName S? "=" S? DirAttributeValue)?)* /* ws: explicit */
[187]    DirAttributeValue    ::=    ('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
[188]    QuotAttrValueContent    ::=    QuotAttrContentChar
| CommonContent
[189]    AposAttrValueContent    ::=    AposAttrContentChar
| CommonContent
[190]    DirElemContent    ::=    DirectConstructor
| CDataSection
| CommonContent
| ElementContentChar
[191]    CommonContent    ::=    PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
[192]    DirCommentConstructor    ::=    "<!--" DirCommentContents "-->" /* ws: explicit */
[193]    DirCommentContents    ::=    ((Char - '-') | ('-' (Char - '-')))* /* ws: explicit */
[194]    DirPIConstructor    ::=    "<?" PITarget (S DirPIContents)? "?>" /* ws: explicit */
[195]    DirPIContents    ::=    (Char* - (Char* '?>' Char*)) /* ws: explicit */
[196]    CDataSection    ::=    "<![CDATA[" CDataSectionContents "]]>" /* ws: explicit */
[197]    CDataSectionContents    ::=    (Char* - (Char* ']]>' Char*)) /* ws: explicit */
[198]    ComputedConstructor    ::=    CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompNamespaceConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor
[199]    CompDocConstructor    ::=    "document" EnclosedExpr
[200]    CompElemConstructor    ::=    "element" (EQName | ("{" Expr "}")) EnclosedContentExpr
[201]    EnclosedContentExpr    ::=    EnclosedExpr
[202]    CompAttrConstructor    ::=    "attribute" (EQName | ("{" Expr "}")) EnclosedExpr
[203]    CompNamespaceConstructor    ::=    "namespace" (Prefix | EnclosedPrefixExpr) EnclosedURIExpr
[204]    Prefix    ::=    NCName
[205]    EnclosedPrefixExpr    ::=    EnclosedExpr
[206]    EnclosedURIExpr    ::=    EnclosedExpr
[207]    CompTextConstructor    ::=    "text" EnclosedExpr
[208]    CompCommentConstructor    ::=    "comment" EnclosedExpr
[209]    CompPIConstructor    ::=    "processing-instruction" (NCName | ("{" Expr "}")) EnclosedExpr
[210]    FunctionItemExpr    ::=    NamedFunctionRef | InlineFunctionExpr
[211]    NamedFunctionRef    ::=    EQName "#" IntegerLiteral /* xgc: reserved-function-names */
[212]    InlineFunctionExpr    ::=    Annotation* ("function" | "fn") FunctionSignature? FunctionBody
[213]    MapConstructor    ::=    "map" "{" (MapConstructorEntry ("," MapConstructorEntry)*)? "}"
[214]    MapConstructorEntry    ::=    MapKeyExpr ":" MapValueExpr
[215]    MapKeyExpr    ::=    ExprSingle
[216]    MapValueExpr    ::=    ExprSingle
[217]    ArrayConstructor    ::=    SquareArrayConstructor | CurlyArrayConstructor
[218]    SquareArrayConstructor    ::=    "[" (ExprSingle ("," ExprSingle)*)? "]"
[219]    CurlyArrayConstructor    ::=    "array" EnclosedExpr
[220]    StringTemplate    ::=    "`" (StringTemplateFixedPart | StringTemplateVariablePart)* "`" /* ws: explicit */
[221]    StringTemplateFixedPart    ::=    ((Char - ('{' | '}' | '`')) | "{{" | "}}" | "``")* /* ws: explicit */
[222]    StringTemplateVariablePart    ::=    EnclosedExpr /* ws: explicit */
[223]    StringConstructor    ::=    "``[" StringConstructorContent "]``" /* ws: explicit */
[224]    StringConstructorContent    ::=    StringConstructorChars (StringInterpolation StringConstructorChars)* /* ws: explicit */
[225]    StringConstructorChars    ::=    (Char* - (Char* ('`{' | ']``') Char*)) /* ws: explicit */
[226]    StringInterpolation    ::=    "`{" Expr? "}`" /* ws: explicit */
[227]    UnaryLookup    ::=    "?" KeySpecifier
[228]    SingleType    ::=    CastTarget "?"?
[229]    TypeDeclaration    ::=    "as" SequenceType
[230]    SequenceType    ::=    ("empty-sequence" "(" ")")
| (ItemType OccurrenceIndicator?)
[231]    OccurrenceIndicator    ::=    "?" | "*" | "+" /* xgc: occurrence-indicators */
[232]    ItemType    ::=    AnyItemTest | TypeName | KindTest | FunctionTest | MapTest | ArrayTest | AtomicOrUnionType | RecordTest | LocalUnionType | EnumerationType | ParenthesizedItemType
[233]    AnyItemTest    ::=    "item" "(" ")"
[234]    AtomicOrUnionType    ::=    EQName
[235]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
[236]    AnyKindTest    ::=    "node" "(" ")"
[237]    DocumentTest    ::=    "document-node" "(" (ElementTest | SchemaElementTest)? ")"
[238]    TextTest    ::=    "text" "(" ")"
[239]    CommentTest    ::=    "comment" "(" ")"
[240]    NamespaceNodeTest    ::=    "namespace-node" "(" ")"
[241]    PITest    ::=    "processing-instruction" "(" (NCName | StringLiteral)? ")"
[242]    AttributeTest    ::=    "attribute" "(" (NameTestUnion ("," TypeName)?)? ")"
[243]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[244]    AttributeDeclaration    ::=    AttributeName
[245]    ElementTest    ::=    "element" "(" (NameTestUnion ("," TypeName "?"?)?)? ")"
[246]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[247]    ElementDeclaration    ::=    ElementName
[248]    AttributeName    ::=    EQName
[249]    ElementName    ::=    EQName
[250]    CastTarget    ::=    TypeName | LocalUnionType | EnumerationType
[251]    TypeName    ::=    EQName
[252]    FunctionTest    ::=    Annotation* (AnyFunctionTest
| TypedFunctionTest)
[253]    AnyFunctionTest    ::=    "function" "(" "*" ")"
[254]    TypedFunctionTest    ::=    "function" "(" (SequenceType ("," SequenceType)*)? ")" "as" SequenceType
[255]    MapTest    ::=    AnyMapTest | TypedMapTest
[256]    AnyMapTest    ::=    "map" "(" "*" ")"
[257]    TypedMapTest    ::=    "map" "(" ItemType "," SequenceType ")"
[258]    RecordTest    ::=    AnyRecordTest | TypedRecordTest
[259]    AnyRecordTest    ::=    "record" "(" "*" ")"
[260]    TypedRecordTest    ::=    "record" "(" FieldDeclaration ("," FieldDeclaration)* ExtensibleFlag? ")"
[261]    FieldDeclaration    ::=    FieldName "?"? ("as" (SequenceType | SelfReference))?
[262]    FieldName    ::=    NCName | StringLiteral
[263]    SelfReference    ::=    ".." OccurrenceIndicator?
[264]    ExtensibleFlag    ::=    "," "*"
[265]    LocalUnionType    ::=    "union" "(" ItemType ("," ItemType)* ")"
[266]    EnumerationType    ::=    "enum" "(" StringLiteral ("," StringLiteral)* ")"
[267]    ArrayTest    ::=    AnyArrayTest | TypedArrayTest
[268]    AnyArrayTest    ::=    "array" "(" "*" ")"
[269]    TypedArrayTest    ::=    "array" "(" SequenceType ")"
[270]    ParenthesizedItemType    ::=    "(" ItemType ")"
[271]    URILiteral    ::=    StringLiteral
[272]    EQName    ::=    QName | URIQualifiedName

A.1.1 Notation

[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"

matches the sequence of characters that appear inside the double quotes.

'string'

matches the sequence of characters that appear inside the single quotes.

[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 operator has higher precedence than alternation; thus A B | C D is identical to (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 alternation; thus A+ | B+ is identical to (A+) | (B+).

A*

matches zero or more occurrences of A. Concatenation has higher precedence than alternation; thus A* | B* is identical to (A*) | (B*)

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 token after the slash is insufficient to allow a parser to distinguish these two possibilities: the * token and keywords like union could be either an operator or a NameTest , and the < token could be either an operator or the start of a DirectConstructor . For example, without lookahead the first part of the expression / * 5 is easily taken to be a complete expression, / *, which has a very different interpretation (the child nodes of /).

If the token 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.

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: 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 XPath 2.0, 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 and XPath 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]. A host language may choose 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).

A host language may choose 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.

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

This section describes how an XQuery 4.0 and XPath 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 . For example, BracedURILiteral does not quality because it appears only in URIQualifiedName, and "0x" does not qualify because it appears only in HexIntegerLiteral.

    The literal terminals in XQuery 4.0 and XPath 4.0 are: ! != # $ % ( ) * + , . .. / // : :: := ; < << <= = =!> => > >= >> ? @ [ ] { | || } × ÷ - allowing ancestor ancestor-or-self and array as ascending at attribute base-uri boundary-space by case cast castable catch child collation comment construction context copy-namespaces count decimal-format decimal-separator declare default descendant descendant-or-self descending digit div document document-node element else empty empty-sequence encoding end enum eq every except exponent-separator external false fn following following-sibling for function ge greatest group grouping-separator gt idiv if import in infinity inherit instance intersect is item item-type lax le least let lt map member minus-sign mod module namespace namespace-node NaN ne next no-inherit no-preserve node of only option or order ordered ordering otherwise parent pattern-separator per-mille percent preceding preceding-sibling preserve previous processing-instruction record return satisfies schema schema-attribute schema-element self sliding some stable start strict strip switch text then to treat true try tumbling type typeswitch union unordered validate value variable version when where window with xquery zero-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 and XPath 4.0 are: BinaryIntegerLiteral CDataSection DecimalLiteral DirCommentConstructor DirElemConstructor DirPIConstructor DoubleLiteral HexIntegerLiteral IntegerLiteral NCName Pragma QName StringConstructor StringLiteral StringTemplate URIQualifiedName Wildcard

  • [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 and XPath 4.0 are: DirElemConstructor Pragma StringConstructor StringTemplate

    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.

      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 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.

A.3.1 Terminal Symbols

[273]    IntegerLiteral    ::=    Digits /* ws: explicit */
[274]    HexIntegerLiteral    ::=    "0x" HexDigits /* ws: explicit */
[275]    BinaryIntegerLiteral    ::=    "0b" BinaryDigits /* ws: explicit */
[276]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[277]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits /* ws: explicit */
[278]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'") /* ws: explicit */
[279]    URIQualifiedName    ::=    BracedURILiteral NCName /* ws: explicit */
[280]    BracedURILiteral    ::=    "Q" "{" (PredefinedEntityRef | CharRef | [^&{}])* "}" /* ws: explicit */
[281]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[282]    EscapeQuot    ::=    '""' /* ws: explicit */
[283]    EscapeApos    ::=    "''" /* ws: explicit */
[284]    ElementContentChar    ::=    (Char - [{}<&])
[285]    QuotAttrContentChar    ::=    (Char - ["{}<&])
[286]    AposAttrContentChar    ::=    (Char - ['{}<&])
[287]    Comment    ::=    "(:" (CommentContents | Comment)* ":)" /* ws: explicit */
/* gn: comments */
[288]    PITarget    ::=    [http://www.w3.org/TR/REC-xml#NT-PITarget]XML /* xgc: xml-version */
[289]    CharRef    ::=    [http://www.w3.org/TR/REC-xml#NT-CharRef]XML /* xgc: xml-version */
[290]    QName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-QName]Names /* xgc: xml-version */
[291]    NCName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-NCName]Names /* xgc: xml-version */
[292]    S    ::=    [http://www.w3.org/TR/REC-xml#NT-S]XML /* xgc: xml-version */
[293]    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.

[294]    Digits    ::=    DecDigit ((DecDigit | "_")* DecDigit)?
[295]    DecDigit    ::=    [0-9]
[296]    HexDigits    ::=    HexDigit ((HexDigit | "_")* HexDigit)?
[297]    HexDigit    ::=    [0-9a-fA-F]
[298]    BinaryDigits    ::=    BinaryDigit ((BinaryDigit | "_")* BinaryDigit)?
[299]    BinaryDigit    ::=    [01]
[300]    CommentContents    ::=    (Char+ - (Char* ('(:' | ':)') Char*))

A.3.2 Terminal Delimitation

XQuery 4.0 and XPath 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: ! != # $ % ( ) * *: , - . .. : :* :: := ; << <= = =!> => > >= >> ? @ [ ] ` `` { {{ | || } }} × ÷ BracedURILiteral ]]> <![CDATA[ --> <!-- /> </ < + #) (# ?> <? S / // ]`` ``[ }` `{ StringLiteral ]

[Definition: The non-delimiting terminal symbols are: allowing ancestor ancestor-or-self and array as at attribute base-uri boundary-space by case cast castable catch child collation comment construction context copy-namespaces count decimal-format decimal-separator declare default descendant descendant-or-self digit div document document-node element else empty empty-sequence encoding end enum eq every except exponent-separator false fn following following-sibling for function ge group grouping-separator gt idiv if import in infinity inherit instance intersect is item item-type lax le let lt map member minus-sign mod module namespace namespace-node NaN ne next no-inherit no-preserve node of only option or order ordered ordering otherwise parent pattern-separator per-mille percent preceding preceding-sibling preserve previous processing-instruction record return satisfies schema schema-attribute schema-element self sliding some stable start strict strip switch text then to treat true try tumbling type typeswitch union unordered validate value variable version when where window with xquery zero-digit ascending BinaryIntegerLiteral DecimalLiteral descending DoubleLiteral external greatest HexIntegerLiteral IntegerLiteral least NCName QName URIQualifiedName ]

[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 "<" (xFF1C, full-width less-than sign) and ">" (xFF1E, full-width greater-than sign) in place of "<" (x3C, less-than sign) and ">" (x3E, 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 x3C (less-than sign) and x3E (greater-than sign) respectively.

A.3.4 End-of-Line Handling

The host language must specify whether the XQuery 4.0 and XPath 4.0 processor normalizes all line breaks on input, before parsing, and if it does so, whether it uses the rules of [XML 1.0] or [XML 1.1].

Note:

XML-based host languages such as XSLT and XSD do not normalize line breaks at the XPath level, because it will already have been done by the host XML parser. Use of character or entity references suppresses normalization of line breaks, so the string literal &#x0D; written within an XSLT-hosted XPath expression represents a string containing a single CR character.

Prior to parsing, the XQuery 4.0 and XPath 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 #xA character:

  1. the two-character sequence #xD #xA

  2. any #xD character that is not immediately followed by #xA.

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 #xA character:

  1. the two-character sequence #xD #xA

  2. the two-character sequence #xD #x85

  3. the single character #x85

  4. the single character #x2028

  5. any #xD character that is not immediately followed by #xA or #x85.

The characters #x85 and #x2028 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 of an XPath expression. 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

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:

Although the keywords switch and typeswitch are not used in XPath, they are considered reserved function names for compatibility with XQuery.

Note:

XQuery and XPath 3.1 added map and array as reserved function names, but this was unnecessary since they 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 union, have not been included in the list.

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 XPath. 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.

# Operator Associativity
1 , (comma) either
2 for, let, FLWOR, some, every, switch, typeswitch, try, if NA
3 or either
4 and either
5 eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >> NA
6 || left-to-right
7 to NA
8 +, - (binary) left-to-right
9 *, div, idiv, mod left-to-right
10 otherwise either
11 union, | either
12 intersect, except left-to-right
13 instance of NA
14 treat as NA
15 castable as NA
16 cast as NA
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 value can be promoted from one type to another. Type promotion is used in evaluating function calls (see 4.6.1.1 Static Function Call Syntax), order by clauses (see 4.17.8 Order By Clause), and operators that accept numeric or string operands (see B.2 Operator Mapping).] The following type promotions are permitted:

  1. Numeric type promotion:

    1. A value of type xs:float (or any type derived by restriction from xs:float) can be promoted to the type xs:double. The result is the xs:double value that is the same as the original value.

    2. A value of type xs:decimal (or any type derived by restriction from xs:decimal) can be promoted to either of the types xs:float or xs:double. The result of this promotion is created by casting the original value to the required type. This kind of promotion may cause loss of precision.

  2. URI type promotion: A value of type xs:anyURI (or any type derived by restriction from xs:anyURI) can be promoted to the type xs:string. The result of this promotion is created by casting the original value to the type xs:string.

    Note:

    Since xs:anyURI values can be promoted to xs:string, functions and operators that compare strings using the default collation also compare xs:anyURI values using the default collation. This ensures that orderings that include strings, xs:anyURI values, or any combination of the two types are consistent and well-defined.

Note that type promotion is different from subtype substitution. For example:

  • A function that expects a parameter $p of type xs:float can be invoked with a value of type xs:decimal. This is an example of type promotion. The value is actually converted to the expected type. Within the body of the function, $p instance of xs:decimal returns false.

  • A function that expects a parameter $p of type xs:decimal can be invoked with a value of type xs:integer. This is an example of subtype substitution. The value retains its original type. Within the body of the function, $p instance of xs:integer returns true.

B.2 Operator Mapping

The operator mapping tables in this section list the combinations of types for which the various operators of XQuery 4.0 and XPath 4.0 are defined. [Definition: For each operator and valid combination of operand types, the operator mapping tables specify a result type and an operator function that 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 values 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.

The and and or operators 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

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:

Operator First operand type Second operand type Result type
+ xs:integer xs:integer xs:integer
+ xs:decimal xs:decimal xs:decimal
+ xs:float xs:float xs:float
+ xs:double xs:double xs: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.)

Binary Operators
Operator Type(A) Type(B) Function Result type
A + B numeric numeric op:numeric-add(A, B) numeric
A + B xs:date xs:yearMonthDuration op:add-yearMonthDuration-to-date(A, B) xs:date
A + B xs:yearMonthDuration xs:date op:add-yearMonthDuration-to-date(B, A) xs:date
A + B xs:date xs:dayTimeDuration op:add-dayTimeDuration-to-date(A, B) xs:date
A + B xs:dayTimeDuration xs:date op:add-dayTimeDuration-to-date(B, A) xs:date
A + B xs:time xs:dayTimeDuration op:add-dayTimeDuration-to-time(A, B) xs:time
A + B xs:dayTimeDuration xs:time op:add-dayTimeDuration-to-time(B, A) xs:time
A + B xs:dateTime xs:yearMonthDuration op:add-yearMonthDuration-to-dateTime(A, B) xs:dateTime
A + B xs:yearMonthDuration xs:dateTime op:add-yearMonthDuration-to-dateTime(B, A) xs:dateTime
A + B xs:dateTime xs:dayTimeDuration op:add-dayTimeDuration-to-dateTime(A, B) xs:dateTime
A + B xs:dayTimeDuration xs:dateTime op:add-dayTimeDuration-to-dateTime(B, A) xs:dateTime
A + B xs:yearMonthDuration xs:yearMonthDuration op:add-yearMonthDurations(A, B) xs:yearMonthDuration
A + B xs:dayTimeDuration xs:dayTimeDuration op:add-dayTimeDurations(A, B) xs:dayTimeDuration
A - B numeric numeric op:numeric-subtract(A, B) numeric
A - B xs:date xs:date op:subtract-dates(A, B) xs:dayTimeDuration
A - B xs:date xs:yearMonthDuration op:subtract-yearMonthDuration-from-date(A, B) xs:date
A - B xs:date xs:dayTimeDuration op:subtract-dayTimeDuration-from-date(A, B) xs:date
A - B xs:time xs:time op:subtract-times(A, B) xs:dayTimeDuration
A - B xs:time xs:dayTimeDuration op:subtract-dayTimeDuration-from-time(A, B) xs:time
A - B xs:dateTime xs:dateTime op:subtract-dateTimes(A, B) xs:dayTimeDuration
A - B xs:dateTime xs:yearMonthDuration op:subtract-yearMonthDuration-from-dateTime(A, B) xs:dateTime
A - B xs:dateTime xs:dayTimeDuration op:subtract-dayTimeDuration-from-dateTime(A, B) xs:dateTime
A - B xs:yearMonthDuration xs:yearMonthDuration op:subtract-yearMonthDurations(A, B) xs:yearMonthDuration
A - B xs:dayTimeDuration xs:dayTimeDuration op:subtract-dayTimeDurations(A, B) xs:dayTimeDuration
A * B numeric numeric op:numeric-multiply(A, B) numeric
A * B xs:yearMonthDuration numeric op:multiply-yearMonthDuration(A, B) xs:yearMonthDuration
A * B numeric xs:yearMonthDuration op:multiply-yearMonthDuration(B, A) xs:yearMonthDuration
A * B xs:dayTimeDuration numeric op:multiply-dayTimeDuration(A, B) xs:dayTimeDuration
A * B numeric xs:dayTimeDuration op:multiply-dayTimeDuration(B, A) xs:dayTimeDuration
A × B numeric numeric op:numeric-multiply(A, B) numeric
A × B xs:yearMonthDuration numeric op:multiply-yearMonthDuration(A, B) xs:yearMonthDuration
A × B numeric xs:yearMonthDuration op:multiply-yearMonthDuration(B, A) xs:yearMonthDuration
A × B xs:dayTimeDuration numeric op:multiply-dayTimeDuration(A, B) xs:dayTimeDuration
A × B numeric xs:dayTimeDuration op:multiply-dayTimeDuration(B, A) xs:dayTimeDuration
A idiv B numeric numeric op:numeric-integer-divide(A, B) xs:integer
A div B numeric numeric op:numeric-divide(A, B) numeric; but xs:decimal if both operands are xs:integer
A div B xs:yearMonthDuration numeric op:divide-yearMonthDuration(A, B) xs:yearMonthDuration
A div B xs:dayTimeDuration numeric op:divide-dayTimeDuration(A, B) xs:dayTimeDuration
A div B xs:yearMonthDuration xs:yearMonthDuration op:divide-yearMonthDuration-by-yearMonthDuration (A, B) xs:decimal
A div B xs:dayTimeDuration xs:dayTimeDuration op:divide-dayTimeDuration-by-dayTimeDuration (A, B) xs:decimal
A ÷ B numeric numeric op:numeric-divide(A, B) numeric; but xs:decimal if both operands are xs:integer
A ÷ B xs:yearMonthDuration numeric op:divide-yearMonthDuration(A, B) xs:yearMonthDuration
A ÷ B xs:dayTimeDuration numeric op:divide-dayTimeDuration(A, B) xs:dayTimeDuration
A ÷ B xs:yearMonthDuration xs:yearMonthDuration op:divide-yearMonthDuration-by-yearMonthDuration (A, B) xs:decimal
A ÷ B xs:dayTimeDuration xs:dayTimeDuration op:divide-dayTimeDuration-by-dayTimeDuration (A, B) xs:decimal
A mod B numeric numeric op:numeric-mod(A, B) numeric
A eq B numeric numeric op:numeric-equal(A, B) xs:boolean
A eq B xs:boolean xs:boolean op:boolean-equal(A, B) xs:boolean
A eq B xs:string xs:string op:numeric-equal(fn:compare(A, B), 0) xs:boolean
A eq B xs:date xs:date op:date-equal(A, B) xs:boolean
A eq B xs:time xs:time op:time-equal(A, B) xs:boolean
A eq B xs:dateTime xs:dateTime op:dateTime-equal(A, B) xs:boolean
A eq B xs:duration xs:duration op:duration-equal(A, B) xs:boolean
A eq B Gregorian Gregorian op:gYear-equal(A, B) etc. xs:boolean
A eq B xs:hexBinary xs:hexBinary op:hexBinary-equal(A, B) xs:boolean
A eq B xs:base64Binary xs:base64Binary op:base64Binary-equal(A, B) xs:boolean
A eq B xs:QName xs:QName op:QName-equal(A, B) xs:boolean
A eq B xs:NOTATION xs:NOTATION op:NOTATION-equal(A, B) xs:boolean
A eq B xs:hexBinary xs:hexBinary op:hexBinary-equal(A, B) xs:boolean
A eq B xs:base64Binary xs:base64Binary op:hexBinary-equal(A, B) xs:boolean
A lt B numeric numeric op:numeric-less-than(A, B) xs:boolean
A lt B xs:boolean xs:boolean op:boolean-less-than(A, B) xs:boolean
A lt B xs:string xs:string op:numeric-less-than(fn:compare(A, B), 0) xs:boolean
A lt B xs:date xs:date op:date-less-than(A, B) xs:boolean
A lt B xs:time xs:time op:time-less-than(A, B) xs:boolean
A lt B xs:dateTime xs:dateTime op:dateTime-less-than(A, B) xs:boolean
A lt B xs:yearMonthDuration xs:yearMonthDuration op:yearMonthDuration-less-than(A, B) xs:boolean
A lt B xs:dayTimeDuration xs:dayTimeDuration op:dayTimeDuration-less-than(A, B) xs:boolean
A lt B xs:hexBinary xs:hexBinary op:hexBinary-less-than(A, B) xs:boolean
A lt B xs:base64Binary xs:base64Binary op:base64Binary-less-than(A, B) xs:boolean
Unary Operators
Operator Operand type Function Result type
+ A numeric op:numeric-unary-plus(A) numeric
- A numeric op: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, and to the parameters that control the serialization process.

C.1 Static Context Components

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 2.3.5 Consistency Constraints.

Static Context Components
Component Default initial value Can be overwritten or augmented by implementation? Can be overwritten or augmented by prolog? Can be overwritten or augmented by expressions? Consistency rules
Statically known namespaces fn, xml, xs, xsi, local overwriteable and augmentable (except for xml) overwriteable and augmentable by 5.13 Namespace Declaration overwriteable and augmentable by element constructor Only one namespace can be assigned to a given prefix per lexical scope.
Default element/type namespace no namespace overwriteable overwriteable by 5.14 Default Namespace Declaration overwriteable by element constructor Only one default namespace per lexical scope.
In-scope variables none augmentable overwriteable and augmentable by 5.16 Variable Declaration and 4.6.2.5 Inline Function Expressions, augmentable by 5.12 Module Import overwriteable and augmentable by variable-binding expressions Only one definition per variable per lexical scope.
Context value static type item() overwriteable overwriteable by 5.17 Context Value Declaration overwriteable by expresssions that set the context value None.
Ordering mode ordered overwriteable overwriteable by 5.7 Ordering Mode Declaration overwriteable by expression Value must be ordered or unordered.
Default function namespace fn overwriteable (not recommended) overwriteable by 5.14 Default Namespace Declaration no None.
In-scope schema types built-in types in xs augmentable augmentable by 5.11 Schema Import no Only one definition per global or local type.
In-scope element declarations none augmentable augmentable by 5.11 Schema Import no Only one definition per global or local element name.
In-scope attribute declarations none augmentable augmentable by 5.11 Schema Import no Only one definition per global or local attribute name.
Statically known function signatures the signatures of the system functions augmentable augmentable 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) no Each function must have a unique expanded QName and number of arguments.
Default collation Unicode codepoint collation overwriteable overwriteable by 5.4 Default Collation Declaration no None.
Construction mode preserve overwriteable overwriteable by 5.6 Construction Declaration no Value must be preserve or strip.
Default order for empty sequences implementation-defined overwriteable overwriteable by 5.8 Empty Order Declaration no Value must be greatest or least.
Boundary-space policy strip overwriteable overwriteable by 5.3 Boundary-space Declaration no Value must be preserve or strip.
Copy-namespaces mode inherit, preserve overwriteable overwriteable by 5.9 Copy-Namespaces Declaration no Value consists of inherit or no-inherit, and preserve or no-preserve.
Static Base URI See rules in 5.5 Base URI Declaration overwriteable overwriteable by 5.5 Base URI Declaration no Value must be a valid lexical representation of the type xs:anyURI.
Statically known decimal formats the default (unnamed) decimal format, which has an implementation-dependent value augmentable augmentable, using decimal format declarations no each QName uniquely identifies a decimal format
Statically known documents none augmentable no no None.
Statically known collections none augmentable no no None.
Statically known default collection type item()* overwriteable no no None.
Statically known collations only the default collation augmentable no no Each URI uniquely identifies a collation.
XPath 1.0 Compatibility Mode false no no no Must be false.
Serialization Parameters
allow-duplicate-names no overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
byte-order-mark implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
cdata-section-elements empty overwriteable and augmentable overwriteable by prolog no Section 3 Serialization Parameters SER31
doctype-public none overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
doctype-system none overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
encoding implementation-defined choice between "utf-8" and "utf-16" overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
escape-solidus yes overwriteable and augmentable overwriteable by prolog yes Section 3 Serialization Parameters SER31
escape-uri-attributes yes overwriteable and augmentable overwriteable by prolog no Section 3 Serialization Parameters SER31
html-version implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
include-content-type yes overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
indent no overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
item-separator implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
json-node-output-method xml overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
media-type implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
method xml overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
normalization-form implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
omit-xml-declaration implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
standalone implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
suppress-indentation empty overwriteable and augmentable overwriteable by prolog no Section 3 Serialization Parameters SER31
undeclare-prefixes no overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31
use-character-maps empty overwriteable and augmentable overwriteable by prolog no Section 3 Serialization Parameters SER31
version implementation-defined overwriteable overwriteable by prolog no Section 3 Serialization Parameters SER31

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 2.3.5 Consistency Constraints.

Dynamic Context Components
Component Default initial value Can be overwritten or augmented by implementation? Can be overwritten or augmented by prolog? Can be overwritten or augmented by expressions? Consistency rules
Context value none overwriteable overwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicates Must be the same in the dynamic context of every module in a query.
Context position none overwriteable overwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicates If context value is defined, context position must be >0 and <= context size; else context position is absentDM31.
Context size none overwriteable overwriteable by a 5.17 Context Value Declaration in the main module overwritten during evaluation of path expressions and predicates If context value is defined, context size must be >0; else context size is absentDM31.
Variable values none augmentable overwriteable and augmentable by 5.16 Variable Declaration and 4.6.2.5 Inline Function Expressions, augmentable by 5.12 Module Import overwriteable and augmentable by variable-binding expressions Names and values must be consistent with in-scope variables.
Named functions the system functions augmentable augmentable by 5.18 Function Declarations, 5.12 Module Import, and 5.11 Schema Import ( (which adds constructor functions for user-defined types) no Must be consistent with statically known function signatures
Current dateTime none must be initialized by implementation no no Must include a timezone. Remains constant during evaluation of a query.
Implicit timezone none must be initialized by implementation no no Remains constant during evaluation of a query.
Available documents none must be initialized by implementation no no None
Available text resources none must be initialized by implementation no no None
Available collections none must be initialized by implementation no no None
Default collection none overwriteable no no None
Available URI collections none must be initialized by implementation no no None
Default URI collection none overwriteable no no None

D Context Components

The tables in this section describe the scope (range of applicability) of the various components in a module's static context and dynamic context.

D.1 Static Context Components

The following table describes the components of the static context. For each component, “global” indicates that the value of the component applies throughout an XPath expression, whereas “lexical” indicates that the value of the component applies only within the subexpression in which it is defined.

Static Context Components
Component Scope
XPath 1.0 Compatibility Mode global
Statically known namespaces global
Default element/type namespace global
Default function namespace global
In-scope schema types global
In-scope element declarations global
In-scope attribute declarations global
In-scope variables lexical; for-expressions, let-expressions, and quantified expressions can bind new variables
Context value static type lexical
Statically known function signatures global
Statically known collations global
Default collation global
Base URI global
Statically known documents global
Statically known collections global
Statically known default collection type global

D.2 Dynamic Context Components

The following table describes how values are assigned to the various components of the dynamic context. All these components are initialized by mechanisms defined by the host language. For each component, “global” indicates that the value of the component remains constant throughout evaluation of the XPath expression, whereas “dynamic” indicates that the value of the component can be modified by the evaluation of subexpressions.

Dynamic Context Components
Component Scope
Context value dynamic; changes during evaluation of path expressions and predicates
Context position dynamic; changes during evaluation of path expressions and predicates
Context size dynamic; changes during evaluation of path expressions and predicates
Variable values dynamic; for-expressions, let-expressions, and quantified expressions can bind new variables
Current date and time global; must be initialized by implementation
Implicit timezone global; must be initialized by implementation
Available documents global; must be initialized by implementation
Available node collections global; must be initialized by implementation
Default collection global; overwriteable by implementation
Available URI collections global; must be initialized by implementation
Default URI collection global; overwriteable by implementation

E 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. Whether the implementation supports the namespace axis.

  10. The default handling of empty sequences returned by an ordering key (orderspec) in an order by clause (empty least or empty greatest).

  11. The names and semantics of any extension expressions (pragmas) recognized by the implementation.

  12. The names and semantics of any option declarations recognized by the implementation.

  13. 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.

  14. 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.)

  15. The means by which serialization is invoked, if the Serialization Feature is supported.

  16. 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.

  17. 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).

  18. Limits on ranges of values for various data types, as enumerated in 6.4 Data Model Conformance.

  19. Syntactic extensions to XQuery, including both their syntax and semantics, as discussed in 6.5 Syntax Extensions.

  20. 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.

  21. The signatures of functions provided by the implementation or via an implementation-defined API (see 2.2.1 Static Context).

  22. Any environment variables provided by the implementation.

  23. Any rules used for static typing (see 2.3.3.1 Static Analysis Phase).

  24. Any serialization parameters provided by the implementation (see 2.3.4 Serialization).

  25. The means by which the location hint for a serialization parameter document identifies the corresponding XDM instance (see 2.3.4 Serialization).

  26. What error, if any, is returned if an external function's implementation does not return the declared result type (see 2.3.5 Consistency Constraints).

  27. Any annotations defined by the implementation, and their associated behavior (see 5.15 Annotations).

  28. Any function assertions defined by the implementation.

  29. The effect of function assertions understood by the implementation on 3.7.3 The judgement subtype-assertions(AnnotationsA, AnnotationsB) .

  30. Any implementation-defined variables defined by the implementation. (see 4.3.2 Variable References).

  31. The ordering associated with fn:unordered in the implementation (see 4.18 Ordered and Unordered Expressions).

  32. Any additional information provided for try/catch via the err:additional variable (see 4.23 Try/Catch Expressions).

  33. The default boundary-space policy (see 5.3 Boundary-space Declaration).

  34. The default collation (see 5.4 Default Collation Declaration).

  35. The default base URI (see 5.5 Base URI Declaration).

F References

F.1 Normative References

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.)
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.
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 ID
World Wide Web Consortium. xml:id Version 1.0. W3C Recommendation. See http://www.w3.org/TR/xml-id/
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 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 Update Facility 3.0
XQuery Update Facility 3.0, John Snelson, Editor. World Wide Web Consortium, 24 January 2017. This version is https://www.w3.org/TR/2017/NOTE-xquery-update-30-20170124/. The latest version is available at https://www.w3.org/TR/xquery-update-30/.
XQuery and XPath Data Model (XDM) 3.1
XQuery and XPath Data Model (XDM) 3.1, Norman Walsh, John Snelson, Andrew Coleman, Editors. World Wide Web Consortium, 21 March 2017. This version is https://www.w3.org/TR/2017/REC-xpath-datamodel-31-20170321/. The latest version is available at https://www.w3.org/TR/xpath-datamodel-31/.
XQuery and XPath Functions and Operators 4.0
XQuery and XPath Functions and Operators 4.0, XSLT Extensions Community Group, World Wide Web Consortium.
XSLT and XQuery Serialization 3.1
XSLT and XQuery Serialization 3.1, Andrew Coleman and Michael Sperberg-McQueen, Editors. World Wide Web Consortium, 21 March 2017. This version is https://www.w3.org/TR/2017/REC-xslt-xquery-serialization-31-20170321/. The latest version is available at https://www.w3.org/TR/xslt-xquery-serialization-31/.

F.2 Non-normative References

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/.
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.
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.)
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.
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/.
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/.
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-QL
Alin Deutsch, Mary Fernandez, Daniela Florescu, Alon Levy, and Dan Suciu. A Query Language for XML.
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
XQL
J. Robie, J. Lapp, D. Schach. XML Query Language (XQL). See http://www.w3.org/TandS/QL/QL98/pp/xql.html.
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/.
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 3.0: 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 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 3.1: An XML Query Language
XQuery 3.1: An XML Query Language, 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-xquery-31-20170321/. The latest version is available at https://www.w3.org/TR/xquery-31/.
XQueryX 3.1
XQueryX 3.1, Jim Melton, Editor. World Wide Web Consortium, 21 March 2017. This version is https://www.w3.org/TR/2017/REC-xqueryx-31-20170321/. The latest version is available at https://www.w3.org/TR/xqueryx-31/.
XSL Transformations (XSLT) Version 3.0
XSL Transformations (XSLT) Version 3.0, Michael Kay, Editor. World Wide Web Consortium, 7 February 2017. This version is https://www.w3.org/TR/2017/CR-xslt-30-20170207/. The latest version is available at https://www.w3.org/TR/xslt-30/.

F.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/.
Moustache
mustache - Logic-less templates. See http://mustache.github.io/mustache.5.html.
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.
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.

G Error Conditions

err:XPST0001

It is a static error if analysis of an expression relies on some component of the static context that is absentDM31 .

err:XPDY0002

It is a dynamic error if evaluation of an expression relies on some part of the dynamic context that is absentDM31 .

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 3.5 Sequence Type Matching.

err:XPST0005

During the analysis phase, it is a static error if the static type assigned to an expression other than the expression () or data(()) is empty-sequence().

err:XPTY0006

During the analysis phase, an expression is classified as implausible if the inferred static type S 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:XPST0010

An implementation that does not support the namespace axis must raise a static error if it encounters a reference to the namespace axis and XPath 1.0 compatibility mode is false.

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] --i.e., each definition must be valid, complete, and unique.

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:XQST0022

It is a static error if a namespace declaration attribute contains an EnclosedExpr.

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 or an 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 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 or variable 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 specified 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 type alias or as a generalized atomic type in the in-scope schema types.

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:

A static error is raised if any of the following conditions is statically detected in any expression:

  • 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 by or 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 an expression 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 error if 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 error if 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 function conversion 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:XPST0140

It is a static error if a self-reference within a RecordTest appears as the type of a field declaration that is not optional and not emptiable.

err:XPTY0141

In a for expression clause, when the keyword member precedes the variable name, the value of the binding collection must be a single array.

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:XPST0147

It is a static error if a type used as a member type in a LocalUnionType is not a generalized atomic type.

H 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.)

H.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.

H.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.

H.2.1 Interoperability Considerations

None known.

H.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.

H.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.

H.2.4 Intended Usage

The intended usage of this media type is for interchange of XQuery expressions.

H.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.

H.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";

H.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" .

H.5 Charset Default Rules

XQuery documents use the Unicode character set and, by default, the UTF-8 encoding.

H.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.

I 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.

arrow operator

The arrow operator applies a function to the value of an expression, using the value as the first argument to the function.

associated value

The value associated with a given key is called the associated value of the key.

atomic value

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

atomization

Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.4 fn:data FO31.

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.

binding collection

The result of evaluating the binding expression in a for expression is called the binding collection

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 4.13.1.4 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.

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 strings FO31.

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 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 braces 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.

context value static type

Context value static type. This is a sequence type; it defines the static type of the context value within the scope of a given expression.

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 4.13.1 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 an expression, 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 an expression, this function always returns the same result.

data model

XQuery 4.0 and XPath 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) 3.1].

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 is the character used to separate the integer part of the number from the fractional part, both in the picture string and in the formatted number; the default value is the period character (.)

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 absentDM31. 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 a namespace URI, or absentDM31. 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 4.17.8 Order By Clause.

default place

Default place. This is a geographical location used to identify the place where events happened (or will happen) when formatting dates and times using functions such as fn:format-date and fn:format-dateTime, 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.

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: ! != # $ % ( ) * *: , - . .. : :* :: := ; << <= = =!> => > >= >> ? @ [ ] ` `` { {{ | || } }} × ÷ BracedURILiteral ]]> <![CDATA[ --> <!-- /> </ < + #) (# ?> <? S / // ]`` ``[ }` `{ 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 is a character used in the picture string to represent an optional digit; the default value is the number sign character (#)

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.

dt-mapping-arrow operator

The mapping arrow operator =!> applies a function to each item in a sequence.

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.

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 type T 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:boolean FO31.

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 braces.

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.

EnumerationType

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 is the character used to separate the mantissa from the exponent in scientific notation both in the picture string and in the formatted number; the default value is the Unicode Latin small letter e character (#x65).

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 FunctionTest. 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 a schema type that is either (a) an atomic type or (b) a pure union type

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 is the character typically used as a thousands separator, both in the picture string and in the formatted number; the default value is the comma character (,)

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.

host-language

A host language for XPath is a language or specification that incorporates XPath as a sublanguage and that defines how the static and dynamic context for evaluation of XPath expressions are to be established.

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 there is a high probability that they were written incorrectly.

implementation defined

Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor 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 implementor 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 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 absentDM31, 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, other than the variable being declared.

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 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 3.1 Predefined 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 value, 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 aliases

Item type aliases. This is a mapping from expanded QName to ItemTypes.

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 value.

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.

may

MAY means that an item is truly optional.

member

The values of an array are called its members.

minus-sign

minus-sign is the single character used to mark negative numbers; the default value is the hyphen-minus character (#x2D).

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 context

The module context for a given module consists of all the information that is accessible to top-level expressions in the 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 item type aliases 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 .

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 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 6 Nodes DM31.

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: allowing ancestor ancestor-or-self and array as at attribute base-uri boundary-space by case cast castable catch child collation comment construction context copy-namespaces count decimal-format decimal-separator declare default descendant descendant-or-self digit div document document-node element else empty empty-sequence encoding end enum eq every except exponent-separator false fn following following-sibling for function ge group grouping-separator gt idiv if import in infinity inherit instance intersect is item item-type lax le let lt map member minus-sign mod module namespace namespace-node NaN ne next no-inherit no-preserve node of only option or order ordered ordering otherwise parent pattern-separator per-mille percent preceding preceding-sibling preserve previous processing-instruction record return satisfies schema schema-attribute schema-element self sliding some stable start strict strip switch text then to treat true try tumbling type typeswitch union unordered validate value variable version when where window with xquery zero-digit ascending BinaryIntegerLiteral DecimalLiteral descending DoubleLiteral external greatest HexIntegerLiteral IntegerLiteral least NCName QName URIQualifiedName

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 numeric type 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 operator function that 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.

ordering mode

Ordering mode. Ordering mode, which has the value ordered or unordered, affects the ordering of the result sequence returned by certain expressions, as discussed in 4.18 Ordered and Unordered Expressions.

ordering mode declaration

An ordering mode declaration sets the ordering mode in the static context, overriding any implementation-defined default.

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 is a character used to separate positive and negative sub-pictures in a picture string; the default value is the semicolon character (;)

percent

percent is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-hundred fraction; the default value is the percent character (%)

per-mille

per-mille is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-thousand fraction; the default value is the Unicode per mille sign character (#x2030)

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.

primary expression

Primary expressions are the basic primitives of the language. They include literals, variable references, context value expressions, 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 item type aliases 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 item type aliases 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: (1) {variety} is union, (2) the {facets} property is empty, (3) no type in the transitive membership of the union type has {variety} list, and (4) 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 values K1 and K2 have the same key value if fn:atomic-equal(K1, K2) returns true, as specified in Section 18.2.1 fn:atomic-equalFO40

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 4.27 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 type that is (or could be) defined using the facilities of [XML Schema 1.0] or [XML Schema 1.1] (including the built-in types).

sequence

A sequence is an ordered collection of zero or more items.

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 and XPath 4.0 expression. The term sequence type suggests that this syntax is used to describe the type of an XQuery 4.0 and XPath 4.0 value, which is always a sequence.

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 3.1].

serialization feature

The Serialization Feature provides means for serializing the result of a query as specified in 2.3.4 Serialization.

setter

Setters are declarations that set the value of some property that affects query processing, such as construction mode, ordering 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 expression, 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 collections

Statically known collections. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of items that would result from calling the fn:collection function with this URI as its argument.

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 default collection type

Statically known default collection type. This is the type of the sequence of items that would result from calling the fn:collection function with no arguments.

statically known documents

Statically known documents. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument.

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.

static typing feature

The Static Typing Feature is an optional feature of XPath that provides support for static semantics, and requires implementations to detect and report type errors during the static analysis phase.

static typing feature

The Static Typing Feature requires implementations to report all type errors during the static analysis phase.

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 2.3 fn:string FO31 function to the node.

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 alias

A type alias is an expanded QName that is mapped to an ItemType in the item type aliases of the static context.

type annotation

Each element node and attribute node in an XDM instance has a type annotation (described in Section 2.7 Schema Information DM31). The type annotation of a node is a reference to an XML 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 3.4 Sequence Types.

typed value

The typed value of a node is a sequence of atomic values and can be extracted by applying the Section 2.4 fn:data FO31 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 value can be promoted from one type to another. Type promotion is used in evaluating function calls (see 4.6.1.1 Static Function Call Syntax), order by clauses (see 4.17.8 Order By Clause), and operators that accept numeric or string operands (see B.2 Operator Mapping).

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 and XPath 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 MU wildcard-matches NU 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. This value is true if rules for backward compatibility with XPath Version 1.0 are in effect; otherwise it is 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 version number

An XQuery version number consists of two integers separated by a dot. The first integer is referred to as the major version number; the second as the minor version number.

xs:anyAtomicType

xs:anyAtomicType is an atomic type that includes all atomic values (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 3.4 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 is the character used to represent the digit zero; the default value is the Unicode digit zero (#x30). 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: 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.

J Example Applications (Non-Normative)

This section contains examples of several important classes of queries that can be expressed using XQuery. The applications described here include joins across multiple data sources, grouping and aggregation, queries based on sequential relationships, recursive transformations, and selection of distinct combinations of values.

Note:

The new features of XQuery 3.0 and XQuery 3.1 can significantly simplify some of these queries.

J.1 Joins

Joins, which combine data from multiple sources into a single result, are a very important type of query. In this section we will illustrate how several types of joins can be expressed in XQuery. We will base our examples on the following three documents:

  1. A document named parts.xml that contains many part elements; each part element in turn contains partno and description subelements.

  2. A document named suppliers.xml that contains many supplier elements; each supplier element in turn contains suppno and suppname subelements.

  3. A document named catalog.xml that contains information about the relationships between suppliers and parts. The catalog document contains many item elements, each of which in turn contains partno, suppno, and price subelements.

A conventional ("inner") join returns information from two or more related sources, as illustrated by the following example, which combines information from three documents. The example generates a “descriptive catalog” derived from the catalog document, but containing part descriptions instead of part numbers and supplier names instead of supplier numbers. The new catalog is ordered alphabetically by part description and secondarily by supplier name.

<descriptive-catalog>
   { 
     for $i in doc("catalog.xml")/items/item,
         $p in doc("parts.xml")/parts/part[partno = $i/partno],
         $s in doc("suppliers.xml")/suppliers
                  /supplier[suppno = $i/suppno]
     order by $p/description, $s/suppname
     return
        <item>
           {
           $p/description,
           $s/suppname,
           $i/price
           }
        </item>
   }
</descriptive-catalog>

The previous query returns information only about parts that have suppliers and suppliers that have parts. An outer join is a join that preserves information from one or more of the participating sources, including elements that have no matching element in the other source. For example, a left outer join between suppliers and parts might return information about suppliers that have no matching parts.

The following query demonstrates a left outer join. It returns names of all the suppliers in alphabetic order, including those that supply no parts. In the result, each supplier element contains the descriptions of all the parts it supplies, in alphabetic order.

for $s in doc("suppliers.xml")/suppliers/supplier
order by $s/suppname
return
   <supplier>
      { 
        $s/suppname,
        for $i in doc("catalog.xml")/items/item
                 [suppno = $s/suppno],
            $p in doc("parts.xml")/parts/part
                 [partno = $i/partno]
        order by $p/description
        return $p/description 
      }
   </supplier>

The previous query preserves information about suppliers that supply no parts. Another type of join, called a full outer join, might be used to preserve information about both suppliers that supply no parts and parts that have no supplier. The result of a full outer join can be structured in any of several ways. The following query generates a list of supplier elements, each containing nested part elements for the parts that it supplies (if any), followed by a list of part elements for the parts that have no supplier. This might be thought of as a “supplier-centered” full outer join. Other forms of outer join queries are also possible.

<master-list>
 {
    for $s in doc("suppliers.xml")/suppliers/supplier
    order by $s/suppname
    return
        <supplier>
           { 
             $s/suppname,
             for $i in doc("catalog.xml")/items/item
                     [suppno = $s/suppno],
                 $p in doc("parts.xml")/parts/part
                     [partno = $i/partno]
             order by $p/description
             return
                <part>
                   {
                     $p/description,
                     $i/price
                   }
                </part> 
           }
        </supplier> 
    ,
    (: parts that have no supplier :)
    <orphan-parts>
       { for $p in doc("parts.xml")/parts/part
         where empty(doc("catalog.xml")/items/item
               [partno = $p/partno] )
         order by $p/description
         return $p/description 
       }
    </orphan-parts>
 }
</master-list>

The previous query uses an element constructor to enclose its output inside a master-list element. The concatenation operator (",") is used to combine the two main parts of the query. The result is an ordered sequence of supplier elements followed by an orphan-parts element that contains descriptions of all the parts that have no supplier.

J.2 Queries on Sequence

XQuery uses the << and >> operators to compare nodes based on document order. Although these operators are quite simple, they can be used to express complex queries for XML documents in which sequence is meaningful. The first two queries in this section involve a surgical report that contains procedure, incision, instrument, action, and anesthesia elements.

The following query returns all the action elements that occur between the first and second incision elements inside the first procedure. The original document order among these nodes is preserved in the result of the query.

let $proc := /report/procedure[1]
for $i in $proc//action
where $i >> ($proc//incision)[1]
   and $i << ($proc//incision)[2]
return $i

It is worth noting here that document order is defined in such a way that a node is considered to precede its descendants in document order. In the surgical report, an action is never part of an incision, but an instrument is. Since the >> operator is based on document order, the predicate $i >> ($proc//incision)[1] is true for any instrument element that is a descendant of the first incision element in the first procedure.

For some queries, it may be helpful to declare a function that can test whether a node precedes another node without being its ancestor. The following function returns true if its first operand precedes its second operand but is not an ancestor of its second operand; otherwise it returns false:

declare function local:precedes($a as node(), $b as node()) 
   as boolean
   {
      $a << $b
        and
      empty($a//node() intersect $b) 
   };

Similarly, a local:follows function could be written:

declare function local:follows($a as node(), $b as node()) 
   as boolean
   {
      $a >> $b
        and
      empty($b//node() intersect $a) 
   };

Using the local:precedes function, we can write a query that finds instrument elements between the first two incisions, excluding from the query result any instrument that is a descendant of the first incision:

let $proc := /report/procedure[1]
for $i in $proc//instrument
where local:precedes(($proc//incision)[1], $i)
   and local:precedes($i, ($proc//incision)[2])
return $i

The following query reports incisions for which no prior anesthesia was recorded in the surgical report. Since an anesthesia is never part of an incision, we can use << instead of the less-efficient local:precedes function:

for $proc in /report/procedure
where some $i in $proc//incision satisfies
         empty($proc//anesthesia[. << $i])
return $proc

In some documents, particular sequences of elements may indicate a logical hierarchy. This is most commonly true of HTML. The following query returns the introduction of an XHTML document, wrapping it in a div element. In this example, we assume that an h2 element containing the text “Introduction” marks the beginning of the introduction, and the introduction continues until the next h2 or h1 element, or the end of the document, whichever comes first.

let $intro := //h2[text()="Introduction"],
    $next-h := //(h1|h2)[. >> $intro][1]
return
   <div>
     {
       $intro,
       if (empty($next-h))
         then //node()[. >> $intro]
         else //node()[. >> $intro and . << $next-h]
     }
   </div>

Note that the above query makes explicit the hierarchy that was implicit in the original document. In this example, we assume that the h2 element containing the text “Introduction” has no subelements.

J.3 Recursive Transformations

Occasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.

Suppose that we need to compute a table of contents for a given document by scanning over the document, retaining only elements named section or title, and preserving the hierarchical relationships among these elements. For each section, we retain subelements named section or title; but for each title, we retain the full content of the element. This might be accomplished by the following recursive function:

declare function local:sections-and-titles($n as node()) as node()? { 
   if (local-name($n) = "section") then 
      element { local-name($n) } { 
         for $c in $n/* 
         return local:sections-and-titles($c) 
      } 
   else if (local-name($n) = "title") then 
      $n 
   else ( ) 
};

The “skeleton” of a given document, containing only its sections and titles, can then be obtained by invoking the local:sections-and-titles function on the root node of the document, as follows:

local:sections-and-titles(doc("cookbook.xml"))

As another example of a recursive transformation, suppose that we wish to scan over a document, transforming every attribute named color to an element named color, and every element named size to an attribute named size. This can be accomplished by the following recursive function (note that the element constructor in case $e generates attributes before child elements):

declare function local:swizzle($n as node()) as node() {
   typeswitch($n) 
   case $a as attribute(color) 
      return element color { string($a) } 
   case $es as element(size) 
      return attribute size { string($es) } 
   case $e as element() 
      return element 
         { local-name($e) } 
         { for $c in 
            ($e/@* except $e/@color,    (: attr -> attr :) 
             $e/size,                   (: elem -> attr :) 
             $e/@color,                 (: attr -> elem :) 
             $e/node() except $e/size ) (: elem -> elem :) 
           return local:swizzle($c) } 
   case $d as document-node() 
      return document 
         { for $c in $d/* return local:swizzle($c) } 
   default return $n 
};

The transformation can be applied to a whole document by invoking the local:swizzle function on the root node of the document, as follows:

local:swizzle(doc("plans.xml"))

J.4 Selecting Distinct Combinations

It is sometimes necessary to search through a set of data to find all the distinct combinations of a given list of properties. For example, an input data set might consist of a large set of order elements, each of which has the same basic structure, as illustrated by the following example:

<order> 
   <date>2003-10-15</date> 
   <product>Dress Shirt</product> 
   <size>M</size> 
   <color>Blue</color>
   <supplier>Fashion Trends</supplier> 
   <quantity>50</quantity>
</order>

From this data set, a user might wish to find all the distinct combinations of product, size, and color that occur together in an order. The following query returns this list, enclosing each distinct combination in a new element named option:

for $p in distinct-values(/orders/order/product), 
    $s in distinct-values(/orders/order/size), 
    $c in distinct-values(/orders/order/color)
order by $p, $s, $c 
return 
   if (exists(/orders/order[product eq $p 
         and size eq $s and color eq $c])) { 
      <option> 
         <product>{$p}</product>
         <size>{$s}</size> 
         <color>{$c}</color> 
      </option> 
   }

K Backwards Compatibility (Non-Normative)

K.1 Incompatibilities relative to XQuery and XPath 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 XQuery 4.0 and XPath 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.

K.2 Incompatibilities relative to XQuery and XPath 3.0

The following names are now reserved, and cannot appear as function names (see A.4 Reserved Function Names):

  • map

  • array

K.3 Incompatibilities relative to XQuery and XPath 2.0 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 and XPath 3.0 and 3.1. In XPath 2.0 XQuery 1.0, it returns false.

Note:

This is not an incompatibility with XQuery and XPath 3.0. It should be included in XQuery and XPath 3.0 as an incompatibility with XPath 2.0 XQuery 1.0, but it was discovered after publication.

K.4 Incompatibilities relative to XPath 1.0

This appendix provides a summary of the areas of incompatibility between XPath 4.0 and [XML Path Language (XPath) Version 1.0]. In each of these cases, an XPath 4.0 processor is compatible with an XPath 2.0, 3.0, or 3.1 processor.

Three separate cases are considered:

  1. Incompatibilities that exist when source documents have no schema, and when running with XPath 1.0 compatibility mode set to true. This specification has been designed to reduce the number of incompatibilities in this situation to an absolute minimum, but some differences remain and are listed individually.

  2. Incompatibilities that arise when XPath 1.0 compatibility mode is set to false. In this case, the number of expressions where compatibility is lost is rather greater.

  3. Incompatibilities that arise when the source document is processed using a schema (whether or not XPath 1.0 compatibility mode is set to true). Processing the document with a schema changes the way that the values of nodes are interpreted, and this can cause an XPath expression to return different results.

K.4.1 Incompatibilities when Compatibility Mode is true

The list below contains all known areas, within the scope of this specification, where an XPath 4.0 processor running with compatibility mode set to true will produce different results from an XPath 1.0 processor evaluating the same expression, assuming that the expression was valid in XPath 1.0, and that the nodes in the source document have no type annotations other than xs:untyped and xs:untypedAtomic.

Incompatibilities in the behavior of individual functions are not listed here, but are included in an appendix of [XQuery and XPath Functions and Operators 4.0].

Since both XPath 1.0 and XPath 4.0 leave some aspects of the specification implementation-defined, there may be incompatibilities in the behavior of a particular implementation that are outside the scope of this specification. Equally, some aspects of the behavior of XPath are defined by the host language.

  1. Consecutive comparison operators such as A < B < C were supported in XPath 1.0, but are not permitted by the XPath 4.0 grammar. In most cases such comparisons in XPath 1.0 did not have the intuitive meaning, so it is unlikely that they have been widely used in practice. If such a construct is found, an XPath 4.0 processor will report a syntax error, and the construct can be rewritten as (A < B) < C

  2. When converting strings to numbers (either explicitly when using the number function, or implicitly say on a function call), certain strings that converted to the special value NaN under XPath 1.0 will convert to values other than NaN under XPath 4.0. These include any number written with a leading + sign, any number in exponential floating point notation (for example 1.0e+9), and the strings INF and -INF.

    Furthermore, the strings Infinity and -Infinity, which were accepted by XPath 1.0 as representations of the floating-point values positive and negative infinity, are no longer recognized. They are converted to NaN when running under XPath 4.0 with compatibility mode set to true, and cause a dynamic error when compatibility mode is set to false.

  3. XPath 4.0 does not allow a token starting with a letter to follow immediately after a numeric literal, without intervening whitespace. For example, 10div 3 was permitted in XPath 1.0, but in XPath 4.0 must be written as 10 div 3.

  4. The namespace axis is deprecated as of XPath 2.0. Implementations may support the namespace axis for backward compatibility with XPath 1.0, but they are not required to do so. (XSLT 2.0 requires that if XPath backwards compatibility mode is supported, then the namespace axis must also be supported; but other host languages may define the conformance rules differently.)

  5. In XPath 1.0, the expression -x|y parsed as -(x|y), and returned the negation of the numeric value of the first node in the union of x and y. In XPath 4.0, this expression parses as (-x)|y. When XPath 1.0 Compatibility Mode is true, this will always cause a type error.

  6. The rules for converting numbers to strings have changed. These may affect the way numbers are displayed in the output of a stylesheet. For numbers whose absolute value is in the range 1E-6 to 1E+6, the result should be the same, but outside this range, scientific format is used for non-integral xs:float and xs:double values.

  7. If one operand in a general comparison is a single atomic value of type xs:boolean, the other operand is converted to xs:boolean when XPath 1.0 compatibility mode is set to true. In XPath 1.0, if neither operand of a comparison operation using the <, <=, > or >= operator was a node set, both operands were converted to numbers. The result of the expression true() > number('0.5') is therefore true in XPath 1.0, but is false in XPath 4.0 even when compatibility mode is set to true.

  8. In XPath 4.0, a type error is raised if the PITarget specified in a SequenceType of form processing-instruction(PITarget) is not a valid NCName. In XPath 1.0, this condition was not treated as an error.

K.4.2 Incompatibilities when Compatibility Mode is false

Even when the setting of the XPath 1.0 compatibility mode is false, many XPath expressions will still produce the same results under XPath 4.0 as under XPath 1.0. The exceptions are described in this section.

In all cases it is assumed that the expression in question was valid under XPath 1.0, that XPath 1.0 compatibility mode is false, and that all elements and attributes are annotated with the types xs:untyped and xs:untypedAtomic respectively.

In the description below, the terms node-set and number are used with their XPath 1.0 meanings, that is, to describe expressions which according to the rules of XPath 1.0 would have generated a node-set or a number respectively.

  1. When a node-set containing more than one node is supplied as an argument to a function or operator that expects a single node or value, the XPath 1.0 rule was that all nodes after the first were discarded. Under XPath 4.0, a type error occurs if there is more than one node. The XPath 1.0 behavior can always be restored by using the predicate [1] to explicitly select the first node in the node-set.

  2. In XPath 1.0, the < and > operators, when applied to two strings, attempted to convert both the strings to numbers and then made a numeric comparison between the results. In XPath 4.0, these operators perform a string comparison using the default collating sequence. (If either value is numeric, however, the results are compatible with XPath 1.0)

  3. When an empty node-set is supplied as an argument to a function or operator that expects a number, the value is no longer converted implicitly to NaN. The XPath 1.0 behavior can always be restored by using the number function to perform an explicit conversion.

  4. More generally, the supplied arguments to a function or operator are no longer implicitly converted to the required type, except in the case where the supplied argument is of type xs:untypedAtomic (which will commonly be the case when a node in a schemaless document is supplied as the argument). For example, the function call substring-before(10 div 3, ".") raises a type error under XPath 4.0, because the arguments to the substring-before function must be strings rather than numbers. The XPath 1.0 behavior can be restored by performing an explicit conversion to the required type using a constructor function or cast.

  5. The rules for comparing a node-set to a boolean have changed. In XPath 1.0, an expression such as $node-set = true() was evaluated by converting the node-set to a boolean and then performing a boolean comparison: so this expression would return true if $node-set was non-empty. In XPath 4.0, this expression is handled in the same way as other comparisons between a sequence and a singleton: it is true if $node-set contains at least one node whose value, after atomization and conversion to a boolean using the casting rules, is true.

    This means that if $node-set is empty, the result under XPath 4.0 will be false regardless of the value of the boolean operand, and regardless of which operator is used. If $node-set is non-empty, then in most cases the comparison with a boolean is likely to fail, giving a dynamic error. But if a node has the value "0", "1", "true", or "false", evaluation of the expression may succeed.

  6. Comparisons of a number to a boolean, a number to a string, or a string to a boolean are not allowed in XPath 4.0: they result in a type error. In XPath 1.0 such comparisons were allowed, and were handled by converting one of the operands to the type of the other. So for example in XPath 1.0 4 = true() returned true; 4 ="+4" returned false (because the string "+4" converts to NaN), and false = "false" returned false (because the string "false" converts to the boolean true). In XPath 3.0 all these comparisons are type errors.

  7. Additional numeric types have been introduced, with the effect that arithmetic may now be done as an integer, decimal, or single- or double-precision floating point calculation where previously it was always performed as double-precision floating point. The result of the div operator when dividing two integers is now a value of type decimal rather than double. The expression 10 div 0 raises an error rather than returning positive infinity.

  8. The rules for converting strings to numbers have changed. The implicit conversion that occurs when passing an xs:untypedAtomic value as an argument to a function that expects a number no longer converts unrecognized strings to the value NaN; instead, it reports a dynamic error. This is in addition to the differences that apply when backwards compatibility mode is set to true.

  9. Many operations in XPath 4.0 produce an empty sequence as their result when one of the arguments or operands is an empty sequence. Where the operation expects a string, an empty sequence is usually considered equivalent to a zero-length string, which is compatible with the XPath 1.0 behavior. Where the operation expects a number, however, the result is not the same. For example, if @width returns an empty sequence, then in XPath 1.0 the result of @width+1 was NaN, while with XPath 4.0 it is (). This has the effect that a filter expression such as item[@width+1 != 2] will select items having no width attribute under XPath 1.0, and will not select them under XPath 4.0.

  10. The typed value of a comment node, processing instruction node, or namespace node under XPath 4.0 is of type xs:string, not xs:untypedAtomic. This means that no implicit conversions are applied if the value is used in a context where a number is expected. If a processing-instruction node is used as an operand of an arithmetic operator, for example, XPath 1.0 would attempt to convert the string value of the node to a number (and deliver NaN if unsuccessful), while XPath 4.0 will report a type error.

  11. In XPath 1.0, it was defined that with an expression of the form A and B, B would not be evaluated if A was false. Similarly in the case of A or B, B would not be evaluated if A was true. This is no longer guaranteed with XPath 4.0: the implementation is free to evaluate the two operands in either order or in parallel. This change has been made to give more scope for optimization in situations where XPath expressions are evaluated against large data collections supported by indexes. Implementations may choose to retain backwards compatibility in this area, but they are not obliged to do so.

  12. In XPath 1.0, the expression -x|y parsed as -(x|y), and returned the negation of the numeric value of the first node in the union of x and y. In XPath 4.0, this expression parses as (-x)|y. When XPath 1.0 Compatibility Mode is false, this will cause a type error, except in the situation where x evaluates to an empty sequence. In that situation, XPath 4.0 will return the value of y, whereas XPath 1.0 returned the negation of the numeric value of y.

K.4.3 Incompatibilities when using a Schema

An XPath expression applied to a document that has been processed against a schema will not always give the same results as the same expression applied to the same document in the absence of a schema. Since schema processing had no effect on the result of an XPath 1.0 expression, this may give rise to further incompatibilities. This section gives a few examples of the differences that can arise.

Suppose that the context node is an element node derived from the following markup: <background color="red green blue"/>. In XPath 1.0, the predicate [@color="blue"] would return false. In XPath 4.0, if the color attribute is defined in a schema to be of type xs:NMTOKENS, the same predicate will return true.

Similarly, consider the expression @birth < @death applied to the element <person birth="1901-06-06" death="1991-05-09"/>. With XPath 1.0, this expression would return false, because both attributes are converted to numbers, which returns NaN in each case. With XPath 4.0, in the presence of a schema that annotates these attributes as dates, the expression returns true.

Once schema validation is applied, elements and attributes cannot be used as operands and arguments of expressions that expect a different data type. For example, it is no longer possible to apply the substring function to a date to extract the year component, or to a number to extract the integer part. Similarly, if an attribute is annotated as a boolean then it is not possible to compare it with the strings "true" or "false". All such operations lead to type errors. The remedy when such errors occur is to introduce an explicit conversion, or to do the computation in a different way. For example, substring-after(@temperature, "-") might be rewritten as abs(@temperature).

In the case of an XPath 4.0 implementation that provides the static typing feature, many further type errors will be reported in respect of expressions that worked under XPath 1.0. For example, an expression such as round(../@price) might lead to a static type error because the processor cannot infer statically that ../@price is guaranteed to be numeric.

Schema validation will in many cases perform whitespace normalization on the contents of elements (depending on their type). This will change the result of operations such as the string-length function.

Schema validation augments the data model by adding default values for omitted attributes and empty elements.

L Change Log (Non-Normative)

This appendix lists the changes that have been made to this specification since the publication of the XQuery 3.1 Recommendation.

This appendix lists the changes that have been made to this specification since the publication of XPath 3.1 Recommendation.

L.1 Changes since version 3.1

L.1.1 Substantive Changes

The following changes have been agreed by the working group:

  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.

  2. 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).

  3. In a static function call, arguments can be specified either positionally or by keyword, or a combination of both.

  4. 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.

  5. Alternative syntax for conditional expressions is available: if (condition) {X} else {Y}, with the else part being optional.

  6. The syntax for $x in X for $y in Y return Z is now accepted in XPath as well as in XQuery.

  7. The NodeTest in an AxisStep now allows alternatives: ancestor::(section|appendix).

  8. Element and attribute tests can include alternative names: element(chapter|section), attribute(role|class).

  9. String templates provide a new way of constructing strings: for example `{$greeting}, {$planet}!` is equivalent to $greeting || ', ' || $planet || '!'

  10. In inline function expressions, the keyword function may be abbreviated as fn.

  11. New abbreviated syntax is introduced (focus function) for simple inline functions taking a single argument. An example is fn{../@code}

  12. The arrow operator => is now complemented by a “mapping arrow” operator =!> which applies a the supplied function to each item in the input sequence independently.

  13. The “function conversion rules” are now renamed “coercion rules”.

  14. The coercion rules allow “relabeling” of a supplied atomic value 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.

  15. In XQuery, 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.

  16. Function coercion 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.

  17. 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.

  18. Support for higher-order functions is now a mandatory feature (in 3.1 it was optional).

  19. Switch expressions now allow a case clause to match multiple atomic values.

  20. Numeric literals can now be written in hexadecimal or binary notation; and underscores can be included for readability.

  21. Switch and typeswitch expressions can now be written with curly braces, to improve readability.

  22. The comparand expression in a switch expression can be omitted, allowing the switch cases to be provided as arbitrary boolean expressions.

  23. The symbols × and ÷ can be used for multiplication and division, and operators such as < and > can use the full-width forms and to avoid the need for XML escaping.

  24. The start clause in window expressions has become optional, as well as the when keyword and its associated expression.

  25. The values true() and false() are allowed in function annotations, and negated numeric literals are also allowed.

  26. 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.

The following changes are present in this draft, but are awaiting review and agreement:

  1. The static context now allows the default namespace for elements and the default namespace for types to be different. XSLT 4.0 takes advantage of this, XQuery 4.0 currently does not.

  2. A new with expression allows namespace bindings to be defined within an expression (and to be redefined in nested expressions).

  3. The static context now allows the unprefixed function names to be resolved using an arbitrary algorithm, rather than requiring the resolution to use a default namespace.

  4. 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.

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

  6. Local union types are added as a new kind of ItemType, constraining the value space of atomic values.

  7. Enumeration types are added as a new kind of ItemType, constraining the value space of strings.

  8. Element and attribute tests of the form element(N) and attribute(N) now allow N to be any NameTest, including a wildcard.

  9. The lookup operator ? can now be followed by a string literal, for cases where map keys are strings other than NCNames.

  10. 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.

  11. A for member clause is added to FLWOR expressions to allow iteration over an array.

L.1.2 Editorial Changes

  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.

  2. 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.