ABSTRACT
Current global communication of people and software applications over the Internet is facilitated by the use of markup languages. This entry introduces the principles and different types of markup, and the history behind the current markup languages. The basis of most of the modern markup languages is the Standard Generalized Markup Language (SGML) or its restricted form Extensible Markup Language (XML). Both of them are metalanguages that are used to define specific markup languages for specific application areas. The entry describes the markup techniques used in SGML and XML, gives examples of their use, and briefly describes some representative SGML and XML applications from different domains. An important factor in the success of XML has been the possibility to reuse markup vocabularies and combine vocabularies originating from different sources. The entry describes the concepts and methods facilitating the reuse of names from earlier defined vocabularies.
