What Is XPath?

XPath is a specification that allows you to address individual parts of an XML document, originally intended for use in the XSLT transformation language and the XPointer syntax for XML fragment identifiers. However, XPath is quite useful on its own, and is available for standalone use in .NET.

Tip

Although XSLT is covered in Chapter 7, XPointer is not implemented in the .NET Framework. Thus, XPointer falls outside of the range of this book. For more information on XPath, XPointer, and their relationship, see John Simpson’s XPath & XPointer (O’Reilly).

XPath 1.0 became a formal recommendation of the W3C in November, 1999, although XPath 2.0 is currently a working draft, still evolving as of this writing. The official XPath recommendation is located on the web at http://www.w3.org/TR/xpath.

The essence of XPath is that you can select certain nodes from within an XML document through a simple XPath expression. In addition, XPath allows you to do some simple string, numeric, and Boolean data transformation on selected nodes. XPath expressions take the form of strings with a certain well-known syntax. This syntax is not explicitly XML itself; it is similar to filesystem pathnames and URLs, and this is where XPath gets its name.

In addition to addressing nodes by name, XPath syntax enables pattern matching, so that you can select individual nodes by their attribute or content values.

In this section, I’ll discuss the structure and syntax of XPath expressions, and some ...

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