SGML:
Can trace its roots back to the 1960s, when its precursor, the Generalized Markup Language (GML) was developed by Charles Goldfarb, Edward Mosher, and Raymond Lorie at IBM in order to help organize the vast amount of documentation that the company was beginning to produce. By1978, the American National Standard Institute (ANSI) took the basics of GML and fashioned a nationwide standard called GCA. Six years later GCA had proved so demonstratively successful at document management, the International Organization for Standardization (ISO) began work on a global version, which became Standard Generalized Markup Language(SGML).

HTML:
Web design is made up of some basic premises, and if you understand them you can design pages that will impress. While the original HTML standard was developed by CERN, new versions are hashed out through a series of online meetings open to anyone on the Internet. Then they are analized, discussed decided and published by the W3 Consortium, led by the Laboratory for Computer Science at the Massachusetts Institute of Technology(MIT) and INRIA, a French technology group, in collaboration with CERN. The W3C has been particularly successful with HTML.

DHTML:
It is actually a combination of web design technologies to create dynamic content on Web pages. Cascading style sheets, Java script are supposed to work together following the rules of the Document Object Model (DOM) the change the content of a page even after it has been loaded into the browser.

XML:
HTML forms part of a large more powerful mark-up language called SGML. In an effort to harness the power of SGML without losing the simplicity of HTML. The W3C has developed Extensible Markup language or XML that can be used to crate your own mark-up Language or XML, that can be used to create your own mark-up languages specifically suited to your topic helping in Custom web site development.