XSLT Overview

XSLT is another markup language based on XML. While I've witnessed quite a few doofus speakers and writers referring to XML itself as a programming language, when it comes to XSLT I think I might agree with them. (I'm sure a few computer science purists might think that even XSLT doesn't qualify as a programming language, but I'm not that dogmatic.) Like the DOM, XSLT deals with XML documents as trees. In very broad terms, XSLT specifies how an input document, referred to as a source tree, is transformed into an output document, referred to as a result tree, based on the contents of an XSLT document called a stylesheet. An XSLT processor is a software component that performs this transformation. The XSLT language uses XPath (XML Path Language), another language defined by a W3C recommendation. Among other things, XPath is used to identify specific parts of the source tree for processing.

XSLT and XPath are both very broad, capable languages. I can't cover all of their depth in just one chapter. However, I don't have to. XSLT and XPath can be used to perform XML transformations for a broad range of applications including not just application integration and electronic commerce but also publishing, word processing, and Web page design. XSLT and XPath were designed primarily to be used with XSL for formatting. People write whole books on each of these two technologies. But the fact of the matter is that most commonly performed business document transformations can be accomplished using a small subset of XSLT and XPath features. So, the basics of what you need to know can be covered in one chapter.

If you want to know more, which you probably will if you work with XSLT very much, there are several places you can go for help. Unlike the Schema Recommendation, I find the XSLT and XPath Recommendations to be well written and easy to understand (for the most part, once you get past the terminology). I highly recommend them. One of the reasons for their readability is that the authors put many of the conformance requirements in separate sections rather than interspersing them with other user-oriented content. On my Web site I also recommend several very good books that deal with more detailed features of XSLT and XPath and offer examples beyond what the Recommendations provide.