SGML is an ISO standard: "ISO 8879:1986 Information processing — Text and office systems — Standard Generalized Markup Language (SGML)", of which there are three versions:
- Original SGML, which was accepted in October 1986, followed by a minor Technical Corrigendum.
- SGML (ENR), in 1996, resulted from a Technical Corrigendum to add extended naming rules allowing arbitrary-language and -script markup.
- SGML (ENR+WWW or WebSGML), in 1998, resulted from a Technical Corrigendum to better support XML and WWW requirements.
The GML, IBM's Generalized Markup Language, was created in 1960's by Charles Goldfarb, Edward Mosher and Raymond Lorie. SGML is the descended form of the GML that is originally aimed at the sharing of the softcopy large-project documents of the industrial, legal and governmental fields as they should be stored in the readable form for many years that is a quite difficult task for the IT. Such fields as the aerospace, technical and industrial publishing industries widely used SGML. However, SGML became even more called-for after the appearance of the XML profile that made it more appropriate for the versatile and all-purpose application.
The logical and physical structure is the obligatory element of any XML document. From the physical point of view, the units that form the document are called the entities. There is a possibility of the entities inclusion in the document in the case of the entity reference to the other entity units. Any document begins with the root elements or the document entity in the other words. From the logical point of view, any document encloses the following elements: declarations, elements, comments, character references and processing instructions. All of these elements are explicitly pointed in the document.
If you are interested in the detailed information concerning the basic, modern SGML syntax, refer to the XML language where you can get the necessary knowledge.