XQuery

Namespace Declarations in Queries

There are three ways that namespaces are mapped to prefixes in XQuery queries:

• Some namespaces are predeclared; no explicit namespace declaration is necessary to associate a prefix with the namespace.

• Namespace declarations can appear in the query prolog.

• Namespace declarations can appear in direct XML constructors.

The examples in this section use the input document cat_ns.xml shown in Example 10-4.

Predeclared Namespaces

For convenience, five commonly used namespace declarations are built into the XQuery recommendation. They are listed in Table 10-1. The five prefixes can be used anywhere in a query even if they are not explicitly declared by a namespace declaration. These prefixes are also used throughout this book to represent the appropriate namespaces.

Table 10-1. Predeclared namespaces

Prefix	Namespace	Uses
xml	http://www.w3.org/XML/1998/namespace	XML attributes such as xml:lang and xml:space
xs	http://www.w3.org/2001/XMLSchema	XML Schema built-in types and their constructors
xsi	http://www.w3.org/2001/XMLSchema-instance	XML Schema instance attributes such as xsi:type and xsi:nil
fn	http://www.w3.org/2005/xpath-functions	XPath Functions Namespace: the default namespace of all built-in functions
local	http://www.w3.org/2005/xquery-local-functions	Functions declared in a main module that are not in a specific namespace

In addition, your XQuery implementation may predeclare other namespaces for use within your ...