CHAPTER 4 XPATH, XPOINTER, XINCLUDE, AND THE
CHAPTER 4 XPATH, XPOINTER, XINCLUDE, AND THE FUTURE 159 The value other does not offer any direction for presenting the resource content but indicates to an XLink application that it should look for other markup for possible instructions. The last value, none, is similar to other. It offers no direction for presenting the resource and means that no other markup may exist to offer direction for an application. XLink Summary This has been an extremely brief look at the XLink technology. It has been around for quite a while, and some people think it will revolutionize Internet browsing. XLink has been a recommended specification for more than four years now, and I don t know about you, but I personally don t have a browser that supports it yet. As far as applications using XLink, I haven t yet come across any, although they must exist. If you are interested in further information on XLink and features not covered here, I suggest you read the specification at http://www.w3.org/TR/xlink/. Introducing XQuery, XPath 2.0, and XSLT 2.0 XPath 2.0 is the new generation of XPath. It serves as the foundation for XQuery and XSLT 2.0. These technologies are still in the working draft phase from the W3C. You can find the specifications at http://www.w3.org/TR/xpath20/, http://www.w3.org/XML/Query, and http:// www.w3.org/TR/xslt20/. This section will introduce you to XPath 2.0. XQuery is almost synonymous with XPath 2.0 at this point, but XSLT 2.0 is out of the scope of this book. Although some of the larger database vendors support XQuery, PHP 5 and libxml do not support these technologies natively at this time (and there is currently no planned support). You may find, however, third-party extensions providing support for these technologies, possibly an extension for a database. For these reasons, I ll present only a brief introduction to XPath 2.0. Like XPath 1.0, XPath 2.0 serves to address nodes within an XML tree. It is meant to be used within a host language, such as XQuery and XSLT 2.0, and not as a stand-alone language. A background on XPath 2.0 should suffice in the event you ever encounter XQuery or XSLT 2.0. XPath 2.0 contains the same node types as 1.0, though the terminology for a root node has changed to document node. XPath 2.0 uses the concept of a sequence. Everything is a sequence, including numbers and strings. For example, a single number would be a sequence with a single number, and a string would be considered a sequence with a single string. A node would be a sequence containing one node. In terms of XPath 1.0, a node set would be a sequence of nodes. Listing 4-9 shows a simplified version of the store document from Listing 4-6. Listing 4-9. Simplified Store Document
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