Though derived from SGML (Standard Generalized Markup Language), Extensible Markup Language (XML) [1] quickly outgrew its initial purpose of enabling large-scale electronic publishing and became the main road of data exchange over the Internet and elsewhere. XML is simple and flexible. These qualities have made XML the perfect instrument for creating new languages in many areas.

For example, HTML is currently the most common language used to create Web pages according to orthodox Web technology, in which the client program is a Web (HTML) browser. However, HTML has its limitations: HTML tags are predefined and cannot be changed or extended.

XML EXTENDS THE WEB AND BUILDS A PLAYGROUND FOR ITS CHILDREN

XML, on the other hand, allows us to create our own elements, attributes, and structures to describe any kind of data. With such flexibility, XML provides the ideal solution for producing new languages to express the ever-increasing complexity of data exchange and other needs.

WAP (Wireless Application Protocol) is, in a way, a child of web technology; but WAP has slightly different requirements, which are not covered by HTML tags. A member of the XML family, WML (Wireless Markup Language) provides the necessary keywords to satisfy these requirements.

XML DESCRIBES BUSINESS RULES AND DATA STRUCTURES; XSLT AND X PATH DESCRIBE THEIR TRANSFORMATIONS

XML is becoming the main tuning tool to describe business rules, data structures, and their transformations.

Extensible Stylesheet Language (XSL) [2] is another member of the same big family of languages.