Extensible Markup Language is a subset of SGML, which provides a way for Web designers to create specific markup for specific needs. Custom markup is easy to designate and create and can be used on any Web site.

XML is intelligent to any level of complexity, and markup definitions can be contained within markup definitions. It is more accurately a "meta language" and is adaptable to any Web presentation need. It is not limited to Web publishing, but that is where XML is currently most relevant: as a replacement for HTML.

When will XML arrive in earnest? What will it mean for us? Who will help us make the transition from HTML-based to XML-based Web publishing? Will there be a transition, after all?

Microsoft wants to help. The company offers some illuminating insights into the meaning of XML, especially regarding its own Internet Explorer browser. Its XML discussion is mixed with an overview of its definition of dynamic HTML. This doctrine is wrapped around IE 4.0, meaning Microsoft's version of XML is intended to work with its browser alone. Microsoft has never really gotten the "universality" of the Web.

As we all wait for XML to become real or just become another failed SGML hybrid, it is worth your while to understand some of the issues and technology.

I enjoy the What the ?XML! Home Page, one of the few available and up-to-date XML meta-index sites. It has lots of attitude and does not read as if it were written by industry lackeys.

The Academic XML Resource Web site has well-written articles that make a strong case for investigating XML.

Less compelling but still useful, the Design Principles for XML site gets into a groove that includes comments such as "XML shall be usable over the Internet" and "XML shall support a wide variety of applications." However, it does offer an overview of what XML might be used for.

If you want the straight poop from Herr XML Himself, check out the Extensible Markup Language page, which contains author Tim Bray's Dec. 8 specification draft, published by the World Wide Web Consortium.

The Whirlwind Guide to SGML Tools and Vendors will help get you in the swing of all things SGML. I found this site a bit dry, but it offers a lot of information and some insight on the SGML/XML connection.

If all else fails, the XML FAQ is a breezily written, informative document that spells out the why, how, where and what-for of this specification.

XML Resources