What is SGML?
SGML, or Standard Generalized Markup Language, is a system of rules for establishing and interchanging a structured document. SGML, formalized by the International Organization for Standards (ISO 8879:1986) in 1986; is used to organize the elements of a particular document or set of documents.
Created by Charles F. Goldfarb in 1974, SGML forms the basis of HTML, XML and a host of others. Mr. Goldfarb comments on www.sgmlsource.com that once created there was a twelve year development period by hundreds of developers leading to the present International Standard.
SGML sets an international standard for definition and standardization of electronic format texts. A key advantage of SGML is that it can be used to create a document from multiple sources; a good example of this is a HTML fragment and a database query. You can also define the document structure using DTD (Document Type Definition) grammar.
SGML is widely used for large document management that incurs regular revisions and updates. Because SGML is so large and complex, it is not yet regularly used on personal computers. Due to the growth of the Internet and certainly the World Wide Web, however, there is renewed interest in SGML because the World Wide Web uses HTML in its web pages. HTML is one way of defining and interpreting tags in accordance with the rules of SGML.
There are three characteristics of SGML that make it unique from other markup languages.
- The emphasis on descriptive markup - a system of codes used to name and categorize parts of a document. Unlike procedural markup that defines what processing is carried out, descriptive markup quite simply defines what the section of the document is. A good example of this type of coding is the <para> tag; that is ‘this item is a paragraph’.
- Types of documents - SGML introduces the idea of document type, and thus is a Document Type Definition (DTD).
- Data independence - SGML is designed to ensure that document encoding is transferable from one environment to another without any loss of information.
Modern society in many ways is built on the foundation of SGML; though most do not realize it. Massively large documents would be impossible to go through without the aid of SGML. For example, a single airplane requires over four million pages of documentation that is regularly updated. This is only possible with SGML.
SGML is a core development tool for defining electronic document structure. As fundamental to the world of electronic text SGML is, it requires dedicated study for a full understanding.
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