Namespace declarations

A namespace declaration is an optional declaration in the XQuery expression prolog that declares a namespace prefix and associates the prefix with a namespace URI.

The declaration adds the prefix-URI pair to the set of statically known namespaces for the expression. The statically known namespaces include all of the namespaces that are known during the static processing of an expression. The namespace declaration is in scope throughout the XQuery expression in which it is declared. Multiple declarations of the same namespace prefix in the query prolog result in an error.

Restriction: The prefixes xmlns and xml are reserved and cannot be specified as a prefix in a namespace declaration.

Syntax

namespace-declaration

prefix

Specifies a namespace prefix that is bound to the URI. The namespace prefix is used in qualified names (QNames) to identify the namespace for an element, attribute, data type, or function.

stringLiteral

Specifies a string literal that represents the URI to which the prefix is bound. The string literal value must be a valid URI and cannot be a zero-length string.

You can override predeclared namespace prefixes by specifying a namespace declarations for those prefixes. However, you cannot override the URI that is associated with the prefix xml.

The string literal cannot be http://www.w3.org/XML/1998/namespace or http://www.w3.org/2000/xmlns/.

Example

The following namespace declaration declares the namespace prefix ns1 and associates it with the namespace URI http://posample.org:

declare namespace ns1 = "http://posample.org";
/ns1:purchaseOrder[shipTo/name = "Jane" and billTo/name = "Jason"]

When the expression in the example executes, the namespace prefix ns1 is associated with the namespace URI http://posample.org. The instance of the purchase order document to which the expression refers is the instance with the namespace URI http://posample.org.