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 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.

SGML was originally designed to enable the sharing of machine-readable documents in large projects in government and the aerospace industry. It has also been used extensively in the printing and publishing industries.

SGML syntax example:

typically something like this 

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

SGML is very flexible and powerful, but its complexity has prevented its widespread application for small-scale general-purpose use.

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.

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

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