SGML (Standard Generalized Markup Language) is a language for defining markup languages. More specifically, SGML is a metalanguage formalism that facilitates the definition of descriptive markup languages for the purpose of electronic information encoding and interchange. SGML supports the definition of markup languages that are hardware- and software-independent, as well as applications-processing neutral. SGML is an International Standard, defined in the document ISO 8879:1986. Information Processing - Text and Office Systems - Standard Generalized Markup Language (SGML), as amended. A key philosophical commitment underlying SGML is separating the representation of information structure and content from information processing specifications. Information objects modeled through an SGML markup language are named and described (using attributes and subelements) in terms of what they are -- from a defined perspective -- not in terms of how they are to be displayed or otherwise processed. Several overviews and introductions to SGML are publicly available on the Internet.
Since SGML itself does not provide for the specification of information processing, or for semantic levels of information description, it is supported by a suite of companion standards. In addition, a recently inaugurated standards effort by W3C is defining a simplified dialect of SGML called XML (Extensible Markup Language), designed to enable 'generic SGML' to be served, received, and processed on the World Wide Web in the same way as is now possible with HTML.
SGML is most often used in the domain of electronic publishing, where much of the essential information ("text") can be represented directly in character data. Major applications of SGML, embodied in 'standard' DTDs ("document type definitions"), are represented broadly in public and private sectors, within government, industry, and academic arenas. A representative listing of SGML applications testifies to the extreme flexibility and generality of SGML in support of markup languages for information management in many domains.
While it is possible to define SGML markup languages as well as to encode and process SGML data without specialized software tools, a broad range of commercial and public-domain software has been developed to assist in the tasks of SGML implementation. Several compilations available on the Internet survey and describe current SGML-based and 'SGML-friendly' software tools that support the needs of corporate enterprises and individual users.
Newcomers to SGML are well-advised to ensure that the information they obtain about SGML is accurate, that software tools they acquire are compliant with the SGML standard, and that the service providers they depend upon are indeed SGML experts. Certification testing for SGML software is not widely used, and even the information referenced in/from this document database cannot be guaranteed free of error. A sensible approach for new users is to depend upon name recognition: find out whether candidate SGML software is rated highly by recognized SGML experts, and whether the industry reputation of a service agency is good. Various lists of vendors, integrators, service providers, and SGML experts are available on the Internet as starting points, but they should be used with caution.
Resources for learning about SGML and developing SGML applications/implementations are now abundant -- although the same could not be said a few years ago. Supporting resources may be accessed through book purchases, software-based tutorials, newsletter subscriptions, SGML user group and SIG membership, conferences and workshops, industry consortium support, online news, electronic mailing lists, or other channels. The Internet provides easy access to information about these resources.
Contact Eamonn Neylon with corrections and updates, or to submit contributions to the ISUG online document database.
