In computer science, a text-formatting language used by publishers and multimedia industries to solve problems arising from incompatibility between text editing, formatting, and database applications.
A document encoded in SGML has information, called markup, that directs how the text is formatted. For instance, the beginning of a chapter might be marked with the text string
SGML evolved from an earlier formatting language called Generalized Markup Language (GML), which was created in the 1960s by IBM. About the same time, the Graphics Communications Association developed a standard, called GenCode, that systematized formatting text between different typesetting systems. Elements of both GML and GenCode are used in SGML.
Other information than text may be included in documents, such as pictures, graphics, sounds, and moving images. A subset of SGML was developed called Hypertext Markup Language (HTML). HTML has become the standard markup language for formatting documents on the interconnected computing network known as the World Wide Web, incorporating text, picture, sound, and moving picture elements.
SGML documents are composed of three types of information: data,structure, and format. Data includes not only text, graphics, sounds, and images but also information that is not presented in the output—for example, a mail-order catalog database may contain reference information on a specific item that is currently out of stock and therefore not included in the printed catalog.
The structure of a document refers to the organization of data in that document. In addition to chapters, a book may contain subchapters, lists, tables, graphics, titles, an index, and a table of contents. World Wide Web pages contain these same structures, but they also contain links, or connections, to other World Wide Web pages. Format refers to a document's appearance.
For example, text may be italicized or altered so that it blinks on a World Wide Web page. Other format variables include indenting, line spacing, type font, type size, and picture and caption placement. Word processing and desktop publishing applications have traditionally inserted markup into documents. The advantage of SGML is that it preserves the data and structure of a document and allows the formatting to be determined at the time of output.
For example, a document may require different formats in order to appear in print, on a CD-ROM disk, and on the World Wide Web. Using SGML, this format information is stored in separate files, one file for each type of formatting. This allows a particular document to be reformatted without information being reentered or altered.
Converting non-SGML data into SGML formats has been expensive and time-consuming for publishing organizations that have changed to SGML. Another challenge lies in training users to work with SGML data. However, because SGML is independent of operating systems and applications, future conversions are unnecessary.
No comments:
Post a Comment