How is XML different from HTML and SGML?
HTML does not have the capacity to represent such detailed information as in the “author” example above. This detail, often called “semantic detail” or “semantic markup” has, however, been effectively conveyed for the past decade or so by SGML. Nonetheless, the technology to work with SGML has remained so difficult to learn and expensive to deploy that information scientists and institutions have little or no time to spare for such steep learning curves and costly ongoing support.. To better understand XML as a markup technology, it actually helps to characterize it with respect to its sibling, HTML, and its parent, SGML. SGML establishes the rules by which any system of markup, such as HTML, can be created. Thus the various forms of markup such as XML and HTML are descended from SGML (in fact, you could characterize HTML as a prodigal son to SGML, with XML as the wiser son-see http://vedavid.org/xml/luke/ for a “marked-up” version of the well-known parable). HTML is not good for data
