XML 101
By Brian Maschhoff

Both XML and HTML are markup languages. HTML tags indicate how content should be displayed in a browser, and XML tags organize content by meaning. For example, a book listing could be structured this way in XML:

<book>
<title>The Milagro Beanfield War</title>
<author>
<firstname>John</firstname>
<lastname>Nichols</lastname>
</author>
<price>$22</price>
<description>A modern tale of the struggle between traditional values and greedy developers in northern New Mexico.</description>
</book>

HTML employs a fixed set of tags, but the possibilities with XML are virtually limitless. New tags can be defined simply by using them, provided the basic rules of XML are followed. Without any additional rules, however, the meaning of the content can become difficult to decipher, particularly for computers.

A set of rules for using and nesting tags is called a schema. XML schemas were originally presented as Data Type Definitions, given XML's origins as a subset of SGML. Unfortunately, the rules for constructing DTDs are rather cryptic, and efforts are under way to formalize a schema standard to describe the rules using XML. An example of this is the XML-Data note submission to the World Wide Web Consortium (W3C) standards body (www.w3.org/TR/1998/NOTE-XML-data-0105/).

XML data exchange will become practical only when the participants agree on a standard, and proof that XML is gaining momentum can be found in the vigorous efforts by various industries and organizations to collectively define schemas for their areas. The premier collection of these can be found at the Organization for the Advancement of Structured Information (OASIS) repository at www.xml.org. Several standards for computer-based instruction have been developed in the last few years. The most recent of these is the Sharable Courseware Object Model (SCORM) released by the Advanced Distributed Learning Initiative (www.adlnet.org), and a schema in DTD format has also been made available.

Though the standards are still evolving, no one should be discouraged from using XML immediately. XML created using one schema can usually be converted to another using XSLT (Extensible Style Language Transformations), yet another goody in the XML tool bag. What's important is to begin creating structured information now.

"When choosing a Web-based training courseware vendor, there's no question that you should make sure they have a plan in place for XML implementation now and in the future," says Forrester Research senior analyst David Troug. "You want as much metadata about that content as possible so that it's as usable as possible, both internally and by other organizations."

Published: August 2000