Chapter 4. Constraining XML

Learning to use XML, both for data representation and within Java applications, is an iterative process. In fact, almost every time you learn something about XML or one of its sister technologies, you will find that it gives you tools to learn yet another subset of the XML picture. Because there are so many XML-related projects and specifications, you will be hard-pressed to "know all there is to know" about XML; and just when you think you do, new versions of things you had down will come out, and you will get to start all over again! However, the more you do understand about the various components that make up the XML technology space, the better equipped you will be to add additional components to your programming toolkit. In keeping with this idea, we will now drop out of the Java programming language and return to XML-related specifications.

Chapter 2 and Chapter 3 should have given you the information and skills to create a well-formed XML document and then manipulate that document to a limited degree within Java. You also should begin to have a basic idea of how XML documents are parsed, and how the SAX Java classes aid in this process. In this chapter, we will discuss constraining the XML documents we have been creating. We will look at how Java can use these constraints in the parsing process in the next chapter.