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XML overview and associated technologies

Extensible Markup Language (XML) is a subset of Standard Generalized Markup Language (SGML). Both XML and SGML are meta languages, because they allow the definition of a chosen set of elements and attributes to meet the requirements of a specific application area. Markup languages are used to annotate information so that it is easier to manipulate and understand. Markup is also used to define how information should be presented for display. One example of this is HTML, which is used to mark up document information so that it can be displayed by a Web browser. The elements within an XML document are organized hierarchically with a single root element at the top of the hierarchy.

XML is a key part of the software infrastructure. It provides a simple and flexible means of defining, creating, and storing data. XML is used for a variety of purposes such as systems configuration, messaging and data storage.

The set of rules that define what can be present in any specific XML document are held in either a document type definition (DTD) or an XML schema definition (XSD). If a DTD or XSD is available, it is possible to check that an XML document is valid. If an XML document is to be usable, it must first be well-formed. This means that it must adhere to all the XML syntax rules as defined in the XML specification document. Only a well-formed XML document can be checked using a DTD or XSD to see if it is valid. A valid XML document is guaranteed to contain only what it should.

Detailed information about XML can be found at:

http://www.w3.org/XML/

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