XQuery

XQuery in Context

XQuery is dependent on or related to a number of other technologies, particularly XPath, XSLT, SQL, and XML Schema. This section explains how XQuery fits in with these technologies.

XQuery and XPath

XPath started out as a language for selecting elements and attributes from an XML document while traversing its hierarchy and filtering out unwanted content. XPath 1.0 is a fairly simple yet useful recommendation that specifies path expressions and a limited set of functions. XPath 2.0 has become much more than that, encompassing a wide variety of expressions and functions, not just path expressions.

XQuery 1.0 and XPath 2.0 overlap to a very large degree. They have the same data model and the same set of built-in functions and operators. XPath 2.0 is essentially a subset of XQuery 1.0. XQuery has a number of features that are not included in XPath, such as FLWORs and XML constructors. This is because these features are not relevant to selecting, but instead have to do with structuring or sorting query results.

The two languages are consistent in that any expression that is valid in both languages evaluates to the same value using both languages.

XPath 2.0 was built with the intention that it would be as backward-compatible with XPath 1.0 as possible. Almost all XPath 1.0 expressions are still valid in XPath 2.0, with a few slight differences in the way values are handled. These differences are identified in Chapter 25.

XQuery Versus XSLT

XSLT is a W3C language for transforming ...