Glossary definition of XML

Also known as: Extensible Markup Language

Extensible Markup Language, or XML, is a language used to describe and structure data. Its predecessor, SGML, is much more diverse, but is too complex for general usage; as a result, a thinned down version was created, which became e X tensible M arkup L anguage. It is used in creating other web-markup methods such as Wireless Markup Language (WML), Scalable Vector Graphics (SVG), or Synchronised Multimedia Integration Language (SMIL).

XML is particularly suitable for web applications because it:

is compatible with web and internet protocols can represent most character sets supports data structures such as records, lists and trees copes with hierarchical document structures; and is independent of any particular equipment or technology.

Unlike HTML (which is a fixed-format language), XML is extensible-which means that its markup symbols are unlimited. Although there are certain similarities between the HTML and XML-both contain markup symbols that describe the contents of a document-HTML is a much laxer language with more room for error and a lot of leniency; as a result, the HTML specification is not always adhered to very strongly, and has different interpretations in each piece of software.

A version of HTML exists that also abides by the stricter rules set by XML, called XHTML. Eventually, HTML should be superceded by this cleaner, standardised and more well defined language.