Extensible Markup Language (XML) represents structured data in text format. XML was designed specifically to meet the challenges of large-scale electronic publishing.

XML is a simple markup language, like HTML, but is also flexible, like SGML. XML is hierarchical, and its main purpose is to describe the structure of data for both humans and computer software to author and read.

Rather than providing a static set of elements which describe various forms of data, XML lets you define elements. As a result, many types of structured data can be described with XML. XML documents can optionally use a document type definition (DTD) or XML schema to define the structure, elements, and attributes that are used in an XML file.

For more detailed information about XML, see  http://www.w3.org/XML/.