Chapter 7. Introduction to XML

If you are thinking about skipping this chapter, please reconsider. While you may never need to be an XML expert, the basic concepts covered here will illuminate why things are done the way they are in the world of web document authoring. Furthermore, if you "get" XML, you'll understand the reasoning that influences all contemporary web design and related W3C Recommendations, from XHTML to CSS 2 and beyond.

XML (Extensible Markup Language) is a W3C standard for text document markup. It is not a language in itself (like HTML), but rather a set of rules for creating other markup languages. In other words, it is a meta-markup language. Languages written according to XML syntax are called XML applications (a confusing use of the word "application" to be sure, but such is the legacy jargon that SGML has left us). If this sounds a bit abstract, think of it this way: XML provides the tools for making up custom sets and subsets of tags.

Although XML began as an effort to improve information structure and handling on the Web, it has quickly taken the entire computing world by storm. In fact, today there is more XML used outside the Web than on it. XML is used for document sharing and data storage in fields as diverse as finance, retail, physics, travel, insurance, and academia, just to name a few. There are also XML files working behind the scenes in an increasing number of software applications, such as Microsoft Office, Macromedia Flash, and Apple iTunes. This is just a testament to the flexibility and robust nature of XML.

XML is having some of its intended impact on the Web as well. It is the cornerstone of the W3C's vision for the future of information exchange over networks.

XML is a complex topic, well beyond the scope of this web design book. This chapter provides an introduction to XML, focusing on the aspects of XML that are useful to web designers and developers, such as how it works, the basic syntax, terminology, and web-based XML applications.

The best way to get a feel for XML is to look at a quick example.