The Extensible Markup Language (XML™) is a data format for structured document interchange on the Web. (extensible because it is not a fixed format like HTML). Both HTML and XML are subsets of SGML.

XML is designed to enable the use of SGML (the international standard metalanguage for markup languages) on the World Wide Web. XML allows developers to create their own markup tags, and share them with others.

The biggest difference between XML and HTML that ALL tags in XML have both start tags and end tags, and all tags must be used in a specific order. (HTML 4 has adopted similar syntax rules.)

The XML standard is relatively new, and there is little development tool support. Consquently, the main users of XML today are programmers, looking to port their client-server applications to the WEB environment. This trend will no doubt continue as XML becomes more widely supported.

But what if you don't want to write applications? Are you going to have to learn how to program in XML? Will your pages disappear from view when the browsers begin supporting XML?

Many of us 'old timers' learned to write HTML using a single browser as our validator. If we could 'see' the page, it was O.K. The problem is, many of us learned 'bad' coding techniques this way - writing code that will not pass a validator.

The problem was further compounded when a new generation of WEB developers began using WYSIWYG editors, such as MS Front Page. They not only didn't understand the code the program generates, they never learned HTML in the first place.

So, what will happen when the browsers begin to process XML code?

An XML processor can read and display clean, valid, HTML - if you are writing 'good' HTML code today, you won't be forced to rewrite your pages later.

There is still time before XML becomes the defacto standard in WEB page design. In the meantime, master the basics, experiment with the newer tools and use a validator to perfect your code. You won't be sorry.

If you would like to learn more about XML, check out the following sites:

XML FAQ - Frequently asked questions (and answers) concerning the status of XML. You'll have to do some scrolling before reaching the Q/A itself - worth the trip.

SGML/XML another FAQ about the XML format - with tons of links to other XML info sites.

XML.com - O'Reilly's Zine offering tools, features, news, and rumours about XML.

W3C - the official site for the XML standard.

Cold Fusion $
Award winning application development tool for the individual or the enterprise. Supports XML standards. Evaluation download available.

XML SPY $
XML Spy is centered around a professional validating XML editor that provides five advanced views on your documents: an Enhanced Grid View for structured editing, a Database/Table view that shows repeated elements in a tabular fashion, a Text View with syntax-coloring for low-level work, a graphical XML Schema design view, and an integrated Browser View that supports both CSS and XSL style-sheets.
Evaluation download available.

EXPAT an Open Source XML Parser Toolkit. It is currently not a validating XML processor. (AUG 2001)

IBM's Developer Portal - XML tutorials for developers.

XML - information on Microsoft's support of the Extensible Markup Language (XML), as well as tutorials for using XML within the MS environment.