XML in a Nutshell, 3rd Edition

Chapter 10. XLinks

XLinks are an attribute-based syntax for attaching links to XML documents. XLinks can be simple Point A-to-Point B links, like the links you’re accustomed to from HTML’s A element. XLinks can also be bidirectional, linking two documents in both directions so you can go from A to B or B to A. XLinks can even be multidirectional, presenting many different paths between any number of XML documents. The documents don’t have to be XML documents—XLinks can be placed in an XML document that lists connections between other documents that may or may not be XML documents themselves. Web graffiti artists take note: these third-party links let you attach links to pages you don’t even control, like the home page of the New York Times or the C.I.A. At its core, XLink is nothing more and nothing less than an XML syntax for describing directed graphs, in which the vertices are documents at particular URIs and the edges are the links between the documents. What you put in that graph is up to you.

Current web browsers at most support simple XLinks that do little more than duplicate the functionality of HTML’s A element. Many browsers, including Internet Explorer, don’t support XLinks at all. However, custom applications may do a lot more. Since XLinks are so powerful, it shouldn’t come as a surprise that they can do more than make blue underlined links on web pages. XLinks can describe tables of contents or indexes. They can connect textual emendations to the text they describe. ...