| What is XML, Anyway? | |
|
An XML document encompasses much more than what people have historically called a document. It can consist of e-commerce transactions, mathematical equations, object metadata, and a thousand other kinds of information. The push to XML stems from the need to create a standard way of understanding, manipulating, and displaying these documents. This standard facilitates exchanging data between applications.
The XML specification defines a standard way to add markup to documents. XML is a subset of the ISO Standard Generalized Markup Language (SGML), which has existed for more than 10 years. SGML is a standard document-formatting language that enables a publisher to create a single document source you can view, display, or print in a variety of ways. However, SGML is a large, complex formatting language, and is unsuited for use over the Web. HTML and XML are simplified versions of SGML designed specifically to support Web development. HTML, another markup language, proves insufficient for this task because tag semantics and the tag set are fixed in HTML. This means sending text in HTML does not tell you anything about the data. All HTML markup tells you is how to display it in a browser. Some browsers support additional tags to enhance viewing a page, but these additional tags don't tell you anything about the data. XML addresses this need, letting you display and define the data in a document. It can do this because it's a metalanguage, which means it doesn't specify semantics or a tag set. |