Extensible Mark Up Language (XML)

XML is a standard, simple, self-describing way of encoding both text and data so that content can be processed with relatively little human intervention and exchanged across diverse hardware, operating systems, and applications.

In brief, XML offers a widely adopted standard way of representing text and data in a format that can be processed without much human or machine intelligence. Information formated in XML can be exchanged across platforms, languages, and applications, and can be used with a wide range of development tools and utilities.

XML is similar enough to HTML in its actual format (both are closely related to the SGML markup definition language that has been an ISO standard since 1986) so that those familiar with HTML can fairly easily pick up basic XML knowledge. But there are two fundamental differences:

• Separation of form and content -- HTML mostly consists of tags defining the appearance of text; in XML the tags generally define the structure and content of the data, with actual appearance specified by a specific application or an associated stylesheet.
• XML is extensible -- tags can be defined by individuals or organizations for some specific application, whereas the HTML standard tagset is defined by the World Wide Web Consortium (W3C).