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XQL uses the XML Path Language (XPath), which is used by both XSL Transformations (XSLT) and XML Pointer Language (XPointer). The following list shows the ways in which XPath is used:

  • Creates expressions that can address parts of an XML document

  • Manipulates strings, numbers, and Boolean operators

  • Matches a set of nodes in a document

XPath models an XML document as a tree of nodes of different types, including element, attribute, and text. XPath expressions can identify these nodes in the XML document based on their type, name, and values, as well as the relationship of a node to other nodes in the document.

An important kind of XPath expression is a location path: an expression that selects a set of nodes relative to the context node. The location path expression has a similar form to a directory structure as shown in a command-line window. The result of evaluating location path is a node set containing the selected nodes.

An XPath expression yields one of the following basic objects:

  • Node set

  • Boolean

  • Number

  • String

The XPath expressions are a core part of XSLT transformations, which associate the objects with templates to create a new XML document. Expressions using the XPath syntax can also be performed directly against the XML Document Object Model (DOM).

For more information about the XML Query Language, XPath, or XPointer, see the World Wide Web Consortium Web site.

In This Section

Qualified Names

Describes the structure of a qualified name.

NaN Values

Describes a NaN, and the types of NaNs.


Provides information about how to use expressions in XQL application development.


Provides a description of patterns. These are expressions that return a set of nodes based on a set of conditions.

Sample Data

Contains the sample data that is used by the examples that appear in the XQL documentation.

XPath Examples

Describes some of the common XPath constructs used in XQL applications.

Location Paths

Provides information about location paths, which are expressions that select a set of nodes relative to the context node.

XPath Syntax

Provides information about the XPath syntax as applicable to MSXML parser.

Related Sections

XML Stylesheet Language Transformations (XSLT)

Describes the XML Stylesheet Language Transformations (XSLT), which provides a mechanism for transforming one class of Extensible Markup Language (XML) document to another.