Sgml (Standard Generalized Markup Language)
SGML is an acronym for Standard Generalized Markup Language. This language was developed and organized by the International Organization for Standards in 1986 as a means for organizing and identifying elements of a document that are destined to be formatted. The identification process is termed marking up. To markup a document is to indicate with symbols or code how a particular piece of text should be formatted; that is, what its appearance will be in the final version. For example, in a word processing document text can be formatted with respect to font, alignment and size, among others considerations.
SGML can also be described as a metalanguage—a means of formally describing a language. As a markup language, SGML specifies what markup is allowed, what markup is required, and how the markup will be distinguished from text. The meaning of the SGML markups is standard, having been developed by the ISO.
SGML is popular for the management of large documents that undergo many revisions and hard copy production in various formats. Many such applications are confined to large computer systems. The complexity of the SGML system has restricted its use on personal computers. However, the explosive use of the World Wide Web has rekindled interest in the use of SGML by personal users, as the World Wide Web uses a language called HyperText Markup Language (HTML). HTML is a means of identifying and interpreting the SGML format tags in a document.
There are three characteristics of SGML that are different from other markup languages: the use of descriptive rather than procedural markup, the document type concept, and its data independence.
The first of these features, descriptive markup, refers to the use of codes to categorize parts of a document. For example, <para> identifies the following portion of a document as a paragraph and </para> indicates that the current paragraph has ended. In contrast, a procedural markup system defines in greater depth what is to be done at certain points in a document. An example of a procedural markup is "move the left margin 2 quads left, skip down one line, and go to the new left margin." SGML is not as detailed because those sort of detailed formatting instructions are resident in separate programs, which can be applied to the document in question. Different processing programs can key on different markup codes within a document. Thus, depending on its intended use, a document can be formatted in various ways.
The second feature, document type, refers to a system whereby documents can be defined according to their component sections and the order of these sections. For example, a report may be defined as consisting of a title, author(s), an abstract and descriptive text and/or graphics. If one or more of these features are not present the document is not recognized as a report and formatted accordingly. The advantage of document type is that documents can be prepared without concern to their format, as formatting will be done automatically afterwards. Technically, this is done using what is known as an SGML parser.
The third feature of SGML, data independence, means that documents can be transferred between different hardware and software environments without loss of information or presentation appearance. This is accomplished by a mechanism called string substitution--a machine-independent way of designating that a particular sting of characters will be replaced by another sting of characters upon document processing.
SGML is most commonly used in electronic publishing in the public, private and academic sectors.
This is the complete article, containing 577 words
(approx. 2 pages at 300 words per page).
