The Extensible Markup Language (XML) is a rulebook for creating data description languages. The XML 1.0 Recommendation, approved by the World Wide Web Consortium in February of 1998, defines a set of constraints for creating languages to identify useful parts of an information set and writing rules against which to validate the description of the information set. The language you use to manipulate the descriptions can be anything: Java, Perl, Python, C++, even Fortran. XML “describes”—it doesn’t “do” anything. XML has its roots in SGML (Standard Generalized Markup Language), an international standard that in part served as the basis for HTML (Hypertext Markup Language).

XML vs. HTML

HTML is a specific language, with a vocabulary of about 80 words (elements/tags). XML is a rulebook for creating your own languages, with no limits on the sizes and definition of the vocabularies.

Why use it?

An XML-based information description language may be used to separate the logical content of an information set from its presentation, allowing an information set to be created (and verified) once, but used many times in many different presentations without being recreated and re-verified.

XML is a tool which may be useful if you need to do two or more things with the same piece of information, like:

	Use it with multiple operating systems (PC/Unix/Mac)
	Use it with different applications (Word/ WordPerfect—Sybase/Oracle/Poet databases)
	Produce different outputs (print/CD-ROM/web)
	Product different versions (long version/Readers’ Digest version)

The more things you do with that single piece of information, the more useful XML may be. XML-encoded data can be used as a bridge between disparate systems, allowing different organizations, applications, and databases to communicate effectively. XML-based languages have been developed for many different types of information; there are applications for the insurance industry, electrical/gas utilities, e-commerce and financial standards, semiconductor manufacturers, and shoes.

XML’s value is in its ability to make the data independent of the tools used to create or manipulate it. XML provides a vendor-, platform- and software-independent solution to information interchange problems.