Standard Generalized Markup Language
Overview
The Standard Generalized Markup Language (SGML) is a markup language standard, developed and maintained by the ISO, that specifies the syntax and semantics of formal markup languages. It is a meta-language, meaning it provides a syntax for defining markup languages. SGML is not a markup language itself, but a description of how to specify one. It is a precursor to both Extensible Markup Language (XML) and Hypertext Markup Language (HTML).
History
SGML originated in the 1960s and 70s from IBM's Generalized Markup Language (GML), which Charles Goldfarb, Edward Mosher, and Raymond Lorie developed. The trio's initials form the "GML" acronym. The development of SGML was heavily influenced by the need for a standard way to exchange and store large documents and databases. In 1986, the ISO adopted SGML as an international standard under ISO 8879.
Syntax and Semantics
SGML's syntax and semantics are defined by a Document Type Definition (DTD), which specifies the rules for the markup. The DTD defines the document's structure, the tags used, and how they should be interpreted. SGML documents consist of text interspersed with markup code, which describes the document's structure and other attributes.
Application and Implementation
SGML is used in large industries and government organizations to manage large amounts of documents and data. The language is particularly suited for documents that undergo frequent revisions and need to be printed or displayed in various formats. Some of the notable applications of SGML include the U.S. Department of Defense's document system, the European Union's legal document system, and the Oxford English Dictionary.
SGML, HTML, and XML
While HTML and XML are both derived from SGML, they serve different purposes. HTML, a specific application of SGML, is used for creating web pages. XML, on the other hand, is a simplified version of SGML designed to be easy to implement and use over the Internet. It is a meta-markup language like SGML but is simpler and less flexible.
Future of SGML
While SGML is not as widely used as it once was due to the rise of XML and HTML, it still has a place in industries and organizations that need to manage large, complex documents. Its future is likely to continue in these specialized areas where its strengths in document management and data integrity are most needed.