by Steven J. Owens (unless otherwise attributed)
Somebody asked what XML is and what's the difference between XML and HTML or DHTML.
In a nutshell, XML is streamlined, simplified SGML. SGML was a good idea, but it was a bear to implement and too big a bite for most everybody who's tried to implement it. The SGML gurus got together, saw how far HTML has gotten because it's simple and accessible, and decided SGML needed to be more accessible to flourish.
SGML is a technology, HTML is an instance; if SGML is ice cream, HTML is french vanilla. Except that after the last four years, it's french vanilla with butterscotch syrup, m&ms, and sprinkles.
Functionally, SGML and XML are standards about standards for documents. They define the terms and formats by which people can define standards for documents - informations. You create a "DTD" (Document Type Definition) in SGML or XML, which defines a new standard type of document. So even if people can't agree on which standard to use, at least they can agree on a protocol to discuss the matter.
This is, of course, an extremely high-level gloss of the topic.
Dynamic HTML? No idea, although Cascading Style Sheets are certainly a lot more SGML-ish than HTML 3.0 font stuff. Theoretically, the next generation of browsers could all be built using an XML spec of next-generation HTML, thus making it easier for the browser developers to incorporate support foreven more and newer data types into their browsers. Or even conceivably make it possible for a browser (or server, or some other software) to learn about a new document type on the fly and adapt to it. This last will defintiely be at the higher end of the scale, however (don't expect to see it soon). (Addendum; in the year or two since the above was written, we're getting a lot closer).