Standard Generalized Markup Language Totally Explained

Everything about Sgml totally explained

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 were used by Goldfarb to make up the term GML).
SGML provides an abstract syntax that can be realized in many different concrete syntaxes. If one defines a concrete syntax in the SGML Declaration, one doesn't need to use "angle brackets" as tag delimiters, although they're the norm — part of the reference concrete syntax defined in the standard. GML used a colon to introduce a tag, a period to end it, and 'e' to indicate an end tag: :xmp.thus:exmp., and SGML is flexible enough to accept that grammar, too.

Original uses

SGML was originally designed to enable the sharing of machine-readable documents in large projects in government, law and 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.
Primarily intended for text and database publishing, one of its first major applications was the second edition of the Oxford English Dictionary (OED), which was and is wholly marked up using an SGML-like markup.

Syntax

SGML allows most aspects of a markup language's syntax to be customized.
   The default syntax appears similar to this example:
typically something like this HTML uses this SGML default syntax.
   Customization of the syntax for a markup language in SGML is specified by a Document Type Definition, or DTD.
   According to the reference syntax, letter case isn't distinguished in tag names so the three tags <quote>, <QUOTE>, and <quOtE> are equivalent (a concrete syntax may change this rule through the NAMECASE NAMING declarations).
   Whether a tag must be paired (like the above <QUOTE></QUOTE> pair) or occurs singly (like an HTML <HR>) is defined in the DTD for the markup language being defined (as long as the OMITTAG feature is enabled). In this case the XML counterpart would be the specific empty tag <hr/>, which is equivalent to the SGML NET-enabling start-tag, introduced in the TC2 (International Standard ISO 8879:1986, Technical Corrigendum 2, Nov. 1999).
   SGML markup languages whose concrete syntax enables the SHORTTAG VALUE feature, don't require attribute values containing only alphanumeric characters to be surrounded by quote marks " (LIT) or ' (LITA), so that the above markup could be written:
typically something like this One feature of SGML markup languages is the NET (Null End Tag) construction: <ITALICS/this/ which is structurally equivalent to <ITALICS>this</ITALICS>. Another is the "presumptuous empty tagging", such that the empty tag </> in <ITALICS>this</> "inherits" its value from the nearest previous nonempty tag, which of course is <ITALICS> (in other words, it closes the most recently opened item). The expression is thus another, more concise, equivalent to <ITALICS>this</ITALICS>. A third is the 'text on the same line' feature, which allows an item to be ended by a line-end (especially useful for headings and the like).
   Additionally, the SHORTTAG NETENABL IMMEDNET feature allows shortening of tags that surround an empty text value:
can be written as
       Where the first "/" stands for the NET-enabling start-tag close (NETSC) and the second one stands for the NET. (Note: XML defines NETSC as "/" and NET and ">" hence, in XML, this construct looks as ).
   SGML is an ISO standard: "ISO 8879:1986 Information processing—Text and office systems—Standard Generalized Markup Language (SGML)" which was accepted in October of 1986.

Derivatives

HTML

World Wide Web Consortium HTML Working Group goes as far as to say, "the Group won't assume that an SGML parser is used for 'classic HTML'".

XML

internationalization. XML is used for general-purpose applications, such as the Semantic Web, XHTML, SVG, RSS, Atom, XML-RPC and SOAP.

DocBook

Other There are also a number of languages that are related in part to SGML and XML, but, because they can't be parsed or validated or otherwise processed using standard SGML and XML tools, can't be considered applications of SGML or XML. One example is the Z Format, a language designed for typesetting and documentation.

Further Information

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