What is XML?

XML stands for eXtensible Markup Language. XML is not just a single language; it's a metalanguage. XML is essentially a set of strict rules that anyone can follow to create their own markup language from scratch. A major strength of XML is the fact that the language describes the information it contains.

XML is an abbreviated form of the Standard Generalized Markup Language (SGML). SGML is the international "mother tongue" with which thousands of document types are described. HTML is an application of SGML and it defines a single, fixed type of document. XML is a subset of SGML and as such it can be used for a wide range of applications.

XML is more streamlined than SGML. It omits the more complicated and rarely used features of SGML. The World Wide Web Consortium (W3C) began developing XML in 1996. The W3C set a number of design goals while they were developing XML. These goals include:

• XML shall be straightforwardly usable over the Internet.
• XML shall support a wide variety of applications.
• XML documents should be human-legible and reasonably clear.
• XML documents shall be easy to create.

Users can design their own document types with XML rather than being limited to the fixed document type of HTML. XML can be customized for specific uses. Users can use XML to make a language that is tailored for a specific purpose or specific industry.

And since XML describes the information, rather than how it is to be displayed or formatted, the same XML document can be filtered through stylesheets to be accessed with a variety of devices. A single file can feed a Web page, a text listing on a handheld electronic organizer, or an audible message for the telephone.

Just like the way browsers like Netscape Navigator and Internet Explorer are used to view HTML pages on the Web, browsers (or parsers) are needed to view XML-based material. As XML is still in the early stages of implementation, XML-enabled browsers are still under development but there are some pilot versions available for experimentation. Microsoft's Internet Explorer versions 4 and 5 can handle some Microsoft-oriented XML but currently they can only convert it to HTML for display. Mozilla, the publicly available Netscape code, has been used in a test implementation of XML. Various software companies and interested parties are working to push past this experimental stage and make XML browsers available.