GML and SGML: First Markup Languages
In the late 1960’s Charles Goldfarb established the principle of modern markup languages whilst working for IBM on a system that would enable specification of documents that could be stored in a database. The documents were to be stored without any presentational information; they were to contain only content and structural information. His work resulted in Generalised Markup Language, an ambitious project that overcame incredible obstacles.
Before GML markup (then called Procedural Markup) was application-specific; they needed a specific text editor and page composition program with its unique markup to process the documents. GML established a uniform set of markup tags.
SGML, the next step in the evolution of the language introduced Document Type Definitions (DTD’s) This allowed the creation of specialised sets of markup tags for different document types. Tim Berners-Lee’s HTML is an SGML document type dealing with marking up hypertext documents.
The World Wide Web
In 1990 Tim Berners-Lee released the world’s first web browser, and launched the world’s first web server, on which he published for discussion the specifications of many of the technologies which run the web today. His HTML language was based on SGML (Standard Generalised Markup Language).
HTML itself has evolved since its inception and a newer version called Extensible Hypertext Markup Language (XHTML), a reformulation of the HTML vocabulary as an Extensible Markup Language (XML) application, which is itself an SGML application.
XML was developed to sit in between HTML and SGML, retaining the simplicity of the former, while providing some of the power and flexibility of the latter. The web of the future will rely heavily on XML, and the World Wide Web Consortium (W3C) has discontinued HTML and recommends moving to XHTML for forward compatibility.