Chapter 10. XML

The Extensible Markup Language (XML) is a document-processing standard that is an official recommendation of the World Wide Web Consortium (W3C), the same group responsible for overseeing the HTML standard. Many expect XML and its sibling technologies to become the markup language of choice for dynamically generated content, including nonstatic web pages. Many companies are already integrating XML support into their products.

XML is actually a simplified form of Standard Generalized Markup Language (SGML), an international documentation standard that has existed since the 1980s. However, SGML is extremely complex, especially for the Web. Much of the credit for XML’s creation can be attributed to Jon Bosak of Sun Microsystems, Inc., who started the W3C working group responsible for scaling down SGML to a form more suitable for the Internet.

Put succinctly, XML is a metalanguage that allows you to create and format your own document markups. With HTML, existing markup is static: <HEAD> and <BODY>, for example, are tightly integrated into the HTML standard and cannot be changed or extended. XML, on the other hand, allows you to create your own markup tags and configure each to your liking—for example, <HeadingA>, <Sidebar>, <Quote>, or <ReallyWildFont>. Each of these elements can be defined through your own document type definitions and stylesheets and applied to one or more XML documents. XML schemas provide another way to define elements. Thus, it is important to ...

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