A markup language is used to add extra information to a text document to control the interpretation of the data it contains. A special character set, such as < and >, is used to separate the markup information from the document data. Interpretation of this extra information naturally requires programs specifically adapted to the particular markup language.

Much programming effort is devoted to creating or interpreting marked up documents, so this lesson takes a detour into markup country before continuing with programming languages.

Markup languages control interpretation of data. You're probably familiar with the way HTML (Hypertext Markup Language) controls the appearance of a marked up page and the possible hypertext link interactions a user can have with the page.

The other highly significant markup language in modern computing is XML (Extensible Markup Language). XML is important in the interpretation, transmission, and storage of all sorts of data. It's extremely likely that you will run into XML marked up documents more and more.

Just a Little History

Markup languages have been created for many purposes. Probably every time some programmer got really frustrated with the effort required to control the exact appearance of printed text or reuse some existing text, they thought about creating a markup language.

A famous example is provided from the programming field. Computer scientist Donald Knuth got annoyed with the poor quality of the typesetting of mathematical expressions in the first volumes of his monumental series of books on programming algorithms. He set about to create a typesetting markup language to improve the situation. The language he invented, called TeX, is widely used in publishing today.

The direct forerunner of HTML and XML was SGML (Standard Generalized Markup Language). GML , which evolved into SGML, was invented at IBM to make the creation of complex program documentation easier. SGML is widely used in industries that have large technical documentation problems, such as aircraft manufacture. It enables you to keep one master document that can be processed (by various programs) in a number of ways to meet a number of different needs. There's that tie-in between markup languages and programming again!

Unfortunately, SGML is so complex that working with it is a full-time job. Too, programs used to display and edit SGML documents are real monsters. The basic idea, however, served as an inspiration for HTML, the markup language of the Web.