Standard Generalized Markup Language

Why SGML was created

Standard Generalized Markup Language is a data encoding that allows the information in documents to be shared -- either by other document publishing systems or by applications for electronic delivery, configuration management, database management, inventory control, etc.

Because it provides a vendor-neutral, formal, international standard for information interchange, SGML is being widely adopted for sharing document-based information in open systems environments.

Benefits of SGML and open systems

There are three key benefits of the open systems approach that employs SGML:

• Investment protection. By putting strategic documents into SGML, organizations protect their information investment from being locked into a single vendor's technology or methodology.
• Data re-usability. By tagging data with its role and any other useful identifiers, SGML allows information to be readily located and re-used.
• Interoperability of applications. SGML is the lingua franca of open systems document applications. This means that customers can choose "best of breed" tools to create, manage or retrieve documents and the data in documents.

History of SGML

While leading IBM research on integrated law office information systems in the 1960s, Charles Goldfarb and his team created a method ("Generalized Markup Language") to let text editing, formatting, and information subsystems share documents. Over the course of nearly two decades and through the efforts of many people and groups, GML eventually gave rise to SGML. In 1986, SGML was adopted as a standard of the International Organization for Standardization (ISO 8879). Since then, it has been increasingly adopted as the international standard for data and document interchange in open system environments, including the automotive, defense, commercial aerospace, pharmaceutical, electronics, and telecommunications industries.

Structure and presentation

Documents comprise three types of information: data, structure, and format.

• The data in a document may include text, graphics, images and even multimedia objects such as video and sound. The data may also include information that does not itself appear on the printed page. For example, a particular graphic of a machine component may have hidden data about what class of machinery uses it, what the tolerances of the component are, and who manufactures it.
• The structure of a document refers to the relationship among the data elements. For example, in this document there are subheadings, paragraphs, and bullet lists. These are each elements of the structure of the document. In a parts catalog, there might also be part numbers, product illustrations, and inventory numbers, some of which might be hidden elements.
• The format of a document is its appearance. In this document, subheadings are printed in boldface text flush against the left margin. They might also be italicized and centered without affecting the structure of the document.

SGML recognizes that data, structure, and format are separable elements. It preserves the data and structure, but does not specify the format of the document -- recognizing that format should be optimized to user requirements at the time of delivery.

Document Type Definition (DTD)

An SGML document has an associated document type definition (DTD) that specifies the rules for the structure of the document; for example, a DTD might specify that the document must have a chapter title and cannot have any part numbers that are not immediately followed by a paragraph describing the part. Several industries have standardized on various DTDs for the different types of documents that they share.

Beyond traditional documents

Because SGML allows data to be tagged with whatever other information might be useful, it can be used to support innovative ways of retrieving information. For example, SGML greatly facilitates the automatic creation of hypertext webs of information that users can navigate freely, following trails of associated information just by pointing and clicking on certain document elements. SGML can also allow systems to build documents on the fly out of networked databases of information. And because SGML is open, it can be used to represent multimedia information, programming code, SGML queries -- virtually any data one may encounter now or in the future.

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