JavaWhat's New in XPath 2.0?

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As of this writing, XPath 2.0 is still in Working Draft form, but it's now stabilized, giving us the chance to work with it. XPath 2.0 is described this way by W3C—just as you'd describe XPath 1.0, in fact:

"The primary purpose of XPath is to address parts of an XML document. XPath uses a compact, non-XML syntax to facilitate use of XPath within URIs and XML attribute values. XPath gets its name from its use of a path notation as in URLs for navigating through the hierarchical structure of an XML document."

Although the primary purpose of XPath hasn't changed in this new version, much of the actual specification has. You'll still be able to use the familiar path steps, each made up of an axis (XPath 2.0 uses the same axes as XPath 1.0), followed by a node test, followed by a predicate. However, much of the terminology has changed, along with some basic concepts—for example, XPath supports sequences instead of node-sets. I go into more detail on this in my book XPath Kick Start : Navigating XML with XPath 1.0 and 2.0.

XPath 2.0, XQuery 1.0, and XSLT 2.0 are all tied together, and XPath 2.0 is the common denominator. The W3C groups working on these standards have been working together closely. One way of looking at what's been going on is that XSLT 2.0 and XQuery 1.0 are designed to share as much as possible—and that what they share is in fact XPath 2.0.

So why XPath 2.0? What's it got that XPath 1.0 doesn't have? There are many answers, but one of the main ones is support for new data types. As you know, XPath 1.0 supports only these data types:

  • string

  • boolean

  • node-set

  • number

That was okay long ago, but things have changed—in particular, W3C has been moving toward XML schema for its data types. Supporting new data types based on XML schema means that XPath 2.0 supports all the simple primitive types built into XML schema. There are 19 such types in all, including many that XPath 1.0 doesn't support, such as data types for dates, URIs, and so on.

The XPath 2.0 data model also supports data types that you can derive from these data types in your own XML schema. We're going to see how to work with these various types ourselves.

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