Learning XML

1.1. What Is XML?

This question is not an easy one to answer. On one level, XML is a protocol for containing and managing information. On another level, it's a family of technologies that can do everything from formatting documents to filtering data. And on the highest level, it's a philosophy for information handling that seeks maximum usefulness and flexibility for data by refining it to its purest and most structured form. A thorough understanding of XML touches all these levels.

Let's begin by analyzing the first level of XML: how it contains and manages information with markup. This universal data packaging scheme is the necessary foundation for the next level, where XML becomes really exciting: satellite technologies such as stylesheets, transformations, and do-it-yourself markup languages. Understanding the fundamentals of markup, documents, and presentation will help you get the most out of XML and its accessories.

1.1.1. Markup

Note that despite its name, XML is not itself a markup language: it's a set of rules for building markup languages. So what exactly is a markup language? Markup is information added to a document that enhances its meaning in certain ways, in that it identifies the parts and how they relate to each other. For example, when you read a newspaper, you can tell articles apart by their spacing and position on the page and the use of different fonts for titles and headings. Markup works in a similar way, except that instead of space, it uses symbols. ...