The Standard Generalized Markup Language (SGML) is a metalanguage in which one can define markup languages for documents. SGML is a descendant of IBM's Generalized Markup Language (GML), developed in the 1960s by Charles Goldfarb, Edward Mosher and Raymond Lorie (whose surname initials also happen to be GML). SGML should not be confused with the Geography Markup Language (GML) developed by the Open GIS Consortium; cf. http://opengis.net/gml/

SGML provides a variety of markup syntaxes that can be used for many applications. By changing the SGML Declaration one does not even need to use "angle brackets" although they are the norm, the so-called concrete reference syntax.

SGML was originally designed to enable the sharing of machine-readable documents in large projects in government and the aerospace industry, which have to remain readable for several decades—a very long time in information technology. It has also been used extensively in the printing and publishing industries, but its complexity has prevented its widespread application for small-scale general-purpose use.

SGML syntax example:

 <QUOTE TYPE="example"> typically something like <ITALICS>this</ITALICS> </QUOTE> 

SGML is an ISO standard: "ISO 8879:1986 Information processing—Text and office systems—Standard Generalized Markup Language (SGML)"

HTML and XML are both derived from SGML. While HTML is an application of SGML, XML is a profile—a specific subset of SGML, designed to be simpler to parse and process than full SGML. Another application of SGML is DocBook, and the Z Format, the former for mostly documentation purposes, the latter for typesetting and documentation.

XML is an attempt to simplify SGML for general-purpose applications, such as the Semantic Web. XML has been used for a large number of applications, including notably XHTML, RSS, XML-RPC and SOAP.

See also: AAP DTD, Document Type Definition

External links

• http://www.y12.doe.gov/sgml/WG8/wg8home.htm - ISO/IEC JTC1/WG4 Web Service: Document Description and Processing Languages
• http://www.w3.org/MarkUp/SGML/ - Overview of SGML Resources at W3C's website