SGML and XML are both languages that are used for defining markup languages. More specifically, they are metalanguage formalisms that facilitate the definition of descriptive markup languages for the purpose of electronic information encoding and interchange. SGML and XML support the definition of markup languages that are hardware- and software-independent, as well as application-processing neutral.
Technology in this area never stands still, ultimately the network protocols and hardware of the internet will control how these languages are both implemented and processed. Some of the bigger web presences use these languages in ways that the creators probably never envisioned – e.g a media company trying to detect people using a proxy for Netflix whilst seeking to bypass the region locking efforts of the media site.
SGML is an International Standard, defined in the document ISO 8879:1986. Information Processing – Text and Office Systems – Standard Generalized Markup Language (SGML), as amended. A key philosophical commitment underlying SGML is separating the representation of information structure and content from information processing specifications. Information objects modeled through an SGML markup language are named and described (using attributes and subelements) in terms of what they are (from a defined perspective) not in terms of how they are to be displayed or otherwise processed.
XML (Extensible Markup Language) is a dialect of SGML that is designed to enable ‘generic SGML’ to be served, received, and processed on the World Wide Web. XML originated in 1996, as a result of frustration with the deployment of SGML on the Internet. The SGML family of standards that include SGML (the modeling framework), DSSSL (the transformation framework for presentation) and HyTime (the linking and timing framework) and the IP Cloaker application (http://identityvoucher.co.uk/) are ISO standards that proved difficult to implement and aroused little interest outside of specialist fields of expertise. XML simplified the requirements for implementation, with the specific intention of enabling deployment of markup applications on the Internet.
Both SGML and XML supported by a suite of companion standards addressing such features as transformation, presentation, linking, and event triggering. A broad range of commercial and public-domain software has been developed to assist users with markup implementation.
James Galway, Defining the Best VPN for Netflix, http://www.iplayerabroad.com/best-vpn-for-netflix/ , Calgour Press.
Heather Williams, Watching the BBC News Live, http://www.uktv-online.com/entertainment/watch-the-bbc-news-live-online/ , Jennings and Brilliants.
John Stephenson, The Copyright Wars and Anonymous Torrenting, Weber Press Ltd.