Summary

If you think of an XML document as a hierarchical tree of data, which it is, then it's not too hard to make a comparison between XML documents and the family trees used in genealogy. This comparison is useful because it turns out that one of the best ways to interact with XML data is by thinking in terms of nodes of data that are related to each other as family members. For example, there are parent, child, and sibling nodes at most points in a document's node tree. XPath is a technology that takes advantage of this hierarchical nature of XML by allowing you to reference parts of XML documents as nodes within a node tree. Although you've heard mention of XPath earlier in the book, this hour formally introduced you to it and explored what it has to offer in terms of referencing XML documents.

XPath plays a role in two other emerging XML technologies, XLink and XPointer, which bring advanced linking support to XML, and at some point to the web. You found out about the theoretical underpinnings of XML linking and what it aims to accomplish. You then learned how to create expressions in XPointer, followed by links in XLink. Although you gained some practical knowledge of XLink and XPointer, there unfortunately is very little support for either technology in major web browsers at the moment. Even so, they are compelling enough technologies that you need to keep an eye out for them potentially making an impact in the XML landscape at some point.