Markup languages (ML), also known as description languages, define the building blocks of a document and specify the relationship in which the individual documents are related to each other. They are text-based and, depending on the application, describe the logical content of documents, their structure and data exchange, or are used to define other markup languages. Anyone, programmer or non-programmer, can read a markup language, but not necessarily interpret it.
Each markup language has its own syntax for describing markups. A distinction is made between the markup languages that describe the representation, the Procedural Markup Languages( PML), and those that describe the information, the Descriptive Markup Languages( DML). In addition to syntax, the semantics of the various markup languages also differ. Markup languages can equally support text documents, graphics, voice or video applications. Markup-labeled documents can be processed by different programs and for different media. For example, for printing, screen display, or voice output.
Typical examples of markup languages are the Standardized Generalized Markup Language( SGML), Hypertext Markup Language( HTML), Extensible Hypertext Markup Language ( XHTML), Wireless Markup Language (WML) and Extensible Markup Language (XML), which are standardized by the International Standards Organization ( ISO).