In the beginning Big Blue (IBM) developed a language, GML, that allowed expression of abstract syntaxes that could later be expressed as a concrete syntax in a specific instance or environment. This meant that I could store a paragraph or sentence or even a word and associate it with a label (tag). Later I defined the tag to display in a 12pt Times New-Roman font, indented 1/2 and inch, with 6 pts of spacing between units. I could also define that tag to display as Courier 48 no spacing in another document. The tags gave me the flexibility to change the way the item looked without changing the item itself, abstract vs concrete.

In October of 1986 ISO adopted SGML, Standard Generalized Markup Language. It went through two major updates, in 1996 and in 1998, to arrive in its current form. The 1996 update extended the naming rules and the 1998 update supported XML and provided better support for the World Wide Web.

Enter HTML. Way back in 1980 Tim Berners-Lee started down the HTML path. By 1989 Berners-Lee and Robert Cailliau each proposed an internet-based hypertext language, which led to collaboration on the W3 hypertext project. By 1991 HTML was public. Although Berners-Lee considered HTML to be an application of SGML, it really wasn’t; it developed its own identity. HTML is know best for web page creation.

XML appears on the scene in 1998, when SGML was updated to include XML. XML is true subset of SGML, and it is extensible as it allows users to define new elements. While XML can be used to create web pages, it combines many standards result in separating the information from the display of the information. The syntax is not platform dependent, making reusability and portability one of its key features.

XHTML, eXtensible Hypertext Markup Language appeared on stage in 2001. This reformulation of HTML conforms to XML good document practices (we’ll talk about what makes a good document at a different time).

Yes, there are many other formats and languages floating around. If you understand the major concepts of SGML, XML, HTML, and XHTML, you have a basis for understanding the tools being developed using these languages. The vocabulary eventually falls into place. And unless you have to start programming in any of these languages, all you really need next is to understand the major document components for each language (they are very similar) and to understand that by separating the content of the document from the look-and-feel of the document opens you to many publishing forms while reusing the original content.