Standard Generalized Markup Language

Standard Generalized Markup Language (SGML) is a generic markup language for representing documents. SGML is an that describes the relationship between a document's content and its structure. SGML allows document-based information to be shared and re-used across applications and computer platforms in an open, vendor-neutral format. SGML is sometimes compared to SQL, in that it enables companies to structure information in documents in an open fashion, so that it can be accessed or re-used by any SGML-aware application across multiple platforms.

Description
SGML is defined in "ISO 8879:1986 Information processing -- Text and office systems -- Standard Generalized Markup Language (SGML)", an ISO standard produced by /SC 18 and amended by "Amendment 1:1988". Unlike other common document file formats that represent both content and presentation, SGML represents a document's content data and structure (interrelationships among the data). Removing the presentation from content establishes a neutral format. SGML documents and the information in them can easily be re-used by publishing and non-publishing applications.

SGML identifies document elements such as titles, paragraphs, tables, and chapters as distinct objects, allowing users to define the relationships between the objects for structuring data in documents. The relationships between document elements are defined in a Document Type Definition (DTD). This is roughly analogous to a collection of field definitions in a database. Once a document is converted into SGML and the information has been 'tagged', it becomes a database-like document. It can be searched, printed or even programmatically manipulated by SGML-aware applications.

Portability and interchange
SGML was developed as an international, platform-independent standard based on ASCII text, so that companies can safely store their documents in SGML without being tied to any particular vendor. The separation of content from presentation facilitates multiple delivery formats like CD-ROM and electronic publishing.

SGML was designed to be a core data standard to enable SGML-aware applications to inter-operate and share data seamlessly. A central SGML document store can feed multiple processes in a company, so managing and updating information is greatly simplified. For example, when an airplane is delivered to a customer, it comes with thousands of pages of documentation. Distributing these on paper is expensive, so companies investigated publishing on CD-ROM. If a maintenance person needs a guide for adjusting a plane's flight surfaces, a viewing tool automatically assembles the relevant information from the document repository as a complete document. SGML can be used to define attributes to information stored in documents such as security levels.

Authoring and conversion
A wide variety of tools were developed to create SGML systems. Mainstream authoring was supported by major word processing vendors like, , and Microsoft. SGML editing and publishing includes traditional SGML authoring tools like, , FrameBuilder and.

SGML conversions became a large market sector because of companies converting legacy data from mainframes, or documents created with mainstream word processors, into SGML. Electronic delivery was regarded as a compelling reason for companies to move to SGML. Electronic delivery enabled users to retrieve information on-line using an intelligent document viewer. Document management and data repositories were the cornerstones driving the development of digital document standards.

Growth and competition
In 1993, the SGML industry was estimated to be worth 520 million and was projected to grow to over $1.46 billion by 1998. However, by 1998, almost all development in SGML was focused on XML - a simpler (and easier to understand and implement) subset of SGML. Apple Computer developed OpenDoc as a competing document container standard, but it failed to gain acceptance and work was discontinued in 1997. PDF, created by Adobe Systems, has since become the free open standard that Mac OS X (now macOS) adopted as its own document interchange format.