Extensible Markup Language (XML)
Extensible Markup Language (XML) is the universal language for describing and exchanging data on the Web. XML was born from an existing international standard called Standard Generalized Markup Language (SGML). SGML was created about 30 years ago in an effort to define a markup language for representing textual information. XML leverages the great work that went into creating SGML (and related standards) by identifying a subset specifically targeted for the Web. Hence, XML is a much smaller and simpler language that is often referred to as containing “20 percent of the complexity and 80 percent of the functionality” of SGML. Thus, like SGML, XML is a facility for creating new markups that provides a file format and data structure for representing data.
It’s a mistake to focus too heavily on XML’s role as a document markup language. The technology’s main benefit is its ability to describe and deliver data. XML is to data what HTML is to display. XML complements , not replaces, HTML.