XQuery 4.0: An XML Query Language

4.12.3.1 Computed Element Constructors

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

The element name is determined by the CompNodeName, which may be provided in a number of ways:

1. As a QName literal, for example:

   element #table {}
element #html:table {}
element #Q{}table {}
element #Q{http://http://www.w3.org/1999/xhtml}table {}element #table {}
element #html:table {}
element #Q{}table {}
element #Q{http://http://www.w3.org/1999/xhtml}table {}
element #Q{http://http://www.w3.org/1999/xhtml}html:table {}element #table {}
element #html:table {}
element #Q{}table {}
element #Q{http://http://www.w3.org/1999/xhtml}table {}
element #Q{http://http://www.w3.org/1999/xhtml}html:table {}

   A QName literal written as an unprefixed lexical QName (the first form above) is resolved using the constructed element namespace rule. This differs from the normal rules for evaluating a QName literal as an atomic item of type xs:QName.

   Note that the last two examples (#Q{}table and #Q{http://http://www.w3.org/1999/xhtml}table) will result in the name of the constructed element having no prefix, which may in turn trigger the generation of a default namespace declaration.Note that the third and fourth examples (#Q{}table and #Q{http://http://www.w3.org/1999/xhtml}table) will result in the name of the constructed element having no prefix, which may in turn trigger the generation of a default namespace declaration.Note that the last twothird and fourth examples (#Q{}table and #Q{http://http://www.w3.org/1999/xhtml}table) will result in the name of the constructed element having no prefix, which may in turn trigger the generation of a default namespace declaration.

2. As a simple EQName, for example:

   element table {}
element html:table {}
element Q{}table {}
element Q{http://http://www.w3.org/1999/xhtml}table {}element table {}
element html:table {}
element Q{}table {}
element Q{http://http://www.w3.org/1999/xhtml}table {}
element Q{http://http://www.w3.org/1999/xhtml}html:table {}element table {}
element html:table {}
element Q{}table {}
element Q{http://http://www.w3.org/1999/xhtml}table {}
element Q{http://http://www.w3.org/1999/xhtml}html:table {}

   In XQuery 4.0 the first form (using an unprefixed lexical QName) is allowed only if the element name is not a reserved keyword (such as div or value): see unreserved-name. In all other cases, the effect is exactly the same as when a leading # is added to turn the EQName into a QName literal.

   This syntax is retained for compatibility, but is deprecated.

3. As an expression in curly brackets. This is processed as follows:

   1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic item of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

   2. If the atomized value of the name expression is of type xs:QName, that expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName.

   3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QNameas follows:

      1. Leading and trailing whitespace is removed.

      2. If the value is a lexical QName, it is expanded using the constructed element namespace rule.

      3. 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.If the value is in the form of a URIQualifiedName (Q{uri}local or Q{uri}prefix:local), it is converted to an expanded QName with the supplied namespace URI and local name, and with the specified prefix if present.If the value is a URIin the form of a -qualified nameURIQualifiedName (Q{uri}local or Q{uri}prefix:local), it is converted to an expanded QName with the supplied namespace URI and local name, and with no prefixthe specified prefix if present.

      Note:

      This was under-specified in XQuery 3.1.

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

The resulting expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName (or its absence).

An error is raised [err:XQDY0096] if the node-name of the constructed element node has any of the following properties:

• Its namespace prefix is xmlns.

• Its namespace URI is http://www.w3.org/2000/xmlns/.

• Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

• Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

The above error may be raised as a static error if the element name is computed statically; in other cases it must be raised as a dynamic error.

The content expression of a computed element constructor (if present) is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1e of 4.12.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. If the content expression is absent, the content sequence is an empty sequence.

Processing of the computed element constructor proceeds as follows:

1. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

3. If the content sequence contains an attribute node or a namespace node following a node that is not an attribute node or a namespace node, a type error is raised [err:XQTY0024].

4. The properties of the newly constructed element node are determined as follows:

   1. node-name is the expanded QName resulting from processing the specified CompNodeName, as described above.

   2. parent is empty.

   3. attributes consist of all the attribute nodes in the content sequence, in implementation-dependent order. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node. If two or more attributes have the same node-name, a dynamic error is raised [err:XQDY0025]. If an attribute named xml:space has a value other than preserve or default, a dynamic error may be raised [err:XQDY0092].

   4. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.

   5. base-uri is set to the following value:

      1. If the constructed node has an attribute named xml:base, then the value of this attribute, resolved (if it is relative) against the Executable Base URI, as described in 2.5.6 Resolving a Relative URI Reference.

      2. Otherwise, the Executable Base URI.

   6. The in-scope namespaces are computed as described in 4.12.4 In-scope Namespaces of a Constructed Element.

   7. The nilled property is false.

   8. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

   9. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

   10. If construction mode in the static context is strip, the type-name property is xs:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.

   11. The is-id and is-idrefs properties are set to false.

A computed element constructor might be used to make a modified copy of an existing element. For example, if the variable $e is bound to an element with numeric content, the following constructor might be used to create a new element with the same name and attributes as $e and with numeric content equal to twice the value of $e:

element { node-name($e) } { $e/@*, 2 * data($e) }

In this example, if $e is bound by the expression let $e := <length units="inches">{ 5 }</length>, then the result of the example expression is the element <length units="inches">10</length>.

One important purpose of computed constructors is to allow the name of a node to be computed. We will illustrate this feature by an expression that translates the name of an element from one language to another. Suppose that the variable $dict is bound to a dictionary element containing a sequence of entry elements, each of which encodes translations for a specific word. Here is an example entry that encodes the German and Italian variants of the word “address”:

<entry word="address">
  <variant xml:lang="de">Adresse</variant>
  <variant xml:lang="it">indirizzo</variant>
</entry>

Suppose further that the variable $e is bound to the following element:

<address>123 Roosevelt Ave. Flushing, NY 11368</address>

Then the following expression generates a new element in which the name of $e has been translated into Italian and the content of $e (including its attributes, if any) has been preserved. The first enclosed expression after the element keyword generates the name of the element, and the second enclosed expression generates the content and attributes:

element {
  $dict/entry[@word = name($e)]/variant[@xml:lang = "it"]
} {
  $e/@*, $e/node()
}

The result of this expression is as follows:

<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>

4.12.3.2 Computed Attribute Constructors

A computed attribute constructor creates a new attribute node, with its own node identity.

Attributes have no default namespace. The rules that expand attribute names create an implementation-dependent prefix if an attribute name has a namespace URI but no prefix is provided.

The attribute name may be provided in a number of ways:

1. As a QName literal, for example:

   attribute #width {}
attribute #xsi:type {}
attribute #Q{}width {}
attribute #Q{http://www.w3.org/2001/XMLSchema-instance}type {}attribute #width {}
attribute #xsi:type {}
attribute #Q{}width {}
attribute #Q{http://www.w3.org/2001/XMLSchema-instance}xsi:type {}
attribute #Q{http://www.w3.org/2001/XMLSchema-instance}type {}attribute #width {}
attribute #xsi:type {}
attribute #Q{}width {}
attribute #Q{http://www.w3.org/2001/XMLSchema-instance}xsi:type {}
attribute #Q{http://www.w3.org/2001/XMLSchema-instance}type {}

   A QName literal written as an unprefixed lexical QName (the first form above) is resolved using the no-namespace ruleno-namespace rule.

   Note that the last example (#Q{http://www.w3.org/2001/XMLSchema-instance}type) will result in the name of the constructed attribute having a system-generated prefix.

2. As a simple EQName, for example:

   attribute width {}
attribute xsi:type {}
attribute Q{}width {}
attribute Q{http://www.w3.org/2001/XMLSchema-instance}type {}attribute width {}
attribute xsi:type {}
attribute Q{}width {}
attribute Q{http://www.w3.org/2001/XMLSchema-instance}xsi:type {}
attribute Q{http://www.w3.org/2001/XMLSchema-instance}type {}attribute width {}
attribute xsi:type {}
attribute Q{}width {}
attribute Q{http://www.w3.org/2001/XMLSchema-instance}xsi:type {}
attribute Q{http://www.w3.org/2001/XMLSchema-instance}type {}

   In XQuery 4.0 the first form (using an unprefixed lexical QName) is allowed only if the attribute name is not a reserved keyword (such as div or value): see unreserved-name. In all other cases, the effect is exactly the same as when a leading # is added to turn the EQName into a QName literal.

   This syntax is retained for compatibility, but is deprecated.

3. As an expression in curly brackets. This is processed as follows:

   1. Atomization is applied to the result of the name expression. If the result of atomization is not a single atomic item of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

   2. If the atomized value of the name expression is of type xs:QName:

      1. If the expanded QName returned by the atomized name expression has a namespace URI but has no prefix, it is given an implementation-dependent prefix.

      2. The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node.

   3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QNameas follows:

      1. Leading and trailing whitespace is removed.

      2. If the value is a lexical QName, it is expanded using the no-namespace rule.

      3. 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.If the value is in the form of a URIQualifiedName (Q{uri}local or Q{uri}prefix:local), it is converted to an expanded QName with the supplied namespace URI, local name, and prefix, or with an implementation dependent prefix if none is supplied.If the value is a URIin the form of a -qualified nameURIQualifiedName (Q{uri}local or Q{uri}prefix:local), it is converted to an expanded QName with the supplied namespace URI and, local name, and prefix, or with an implementation dependent prefix if none is supplied.

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

      Note:

      This was under-specified in XQuery 3.1.

The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

If the keyword attribute is followed by a name expression, the name expression is processed as follows:

A dynamic error is raised [err:XQDY0044] if the node-name of the constructed attribute node has any of the following properties:

• Its namespace prefix is xmlns.

• It has no namespace prefix and its local name is xmlns.

• Its namespace URI is http://www.w3.org/2000/xmlns/.

• Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

• Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

The content expression of a computed attribute constructor is processed as follows:

1. Atomization is applied to the result of the content expression, converting it to a sequence of atomic items. (If the content expression is absent, the result of this step is an empty sequence.)

2. If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic item in the atomized sequence is cast into a string.

3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the string-value property of the new attribute node. The type annotation (type-name property) of the new attribute node is xs:untypedAtomic. The typed-value property of the attribute node is the same as its string-value, as an instance of xs:untypedAtomic.

4. The parent property of the attribute node is set to empty.

5. If the attribute name is xml:id, then xml:id processing is performed as defined in [XML ID]. This ensures that the attribute node has the type xs:ID and that its value is properly normalized. If an error is encountered during xml:id processing, an implementation may raise a dynamic error [err:XQDY0091].

6. If the attribute name is xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.

7. If the attribute name is xml:space and the attribute value is other than preserve or default, a dynamic error may be raised [err:XQDY0092].

• Example:

  attribute size { 4 + 3 }

  The string value of the size attribute is "7" and its type is xs:untypedAtomic.

• Example:

  attribute {
    if ($sex = "M") then "husband" else "wife"
  } {
    <a>Hello</a>, 1 to 3, <b>Goodbye</b>
  }

  The name of the constructed attribute is either husband or wife. Its string value is "Hello 1 2 3 Goodbye".