XLinks and XPointers

It's hard to imagine the World Wide Web without hyperlinks , and, of course, HTML documents excel at letting you link from one to another. How about XML? In XML, it turns out, you use XLinks and XPointers.

XLinks let any element become a link, not just a single element as with the HTML <A> element. That's a good thing because XML doesn't have a built-in <A> element. In XML, you define your own elements, and it only makes sense that you can define which of those represent links to other documents.

In fact, XLinks are more powerful than simple hyperlinks. XLinks can be bidirectional, allowing the user to return after following a link. They can even be multidirectionalin fact, they can be sophisticated enough to point to the nearest mirror site from which a resource can be fetched .

XPointers, on the other hand, point not to a whole document, but to a part of a document. In fact, XPointers are smart enough to point to a specific element in a document, or the second instance of such an element, or the 11,904th instance. They can even point to the first child element of another element, and so on. The idea is that XPointers are powerful enough to locate specific parts of another document without forcing you to add more markup to the target document.

On the other hand, the whole idea of XLinks and XPointers is relatively new and not fully implemented in any browser. We will see what's possible today later in this book.

Here are some XLink and XPointer references onlinetake a look for more information on these topics:

• www.w3.org/TR/xlink/ The W3C XLink page

• www.w3.org/TR/xptr The W3C XPointer page