What's the big deal about XML?

-- Industrial Distribution, 1/1/2001

As a system of marking up or "tagging" a document so that it can be published on the World Wide Web, HyperText Markup Language (HTML) has become one of the cornerstones of the Information Age. While it is likely to remain the industry standard, many of today's leading Web developers are looking for more powerful and flexible capabilities to power their Web applications. They are increasingly looking toward Extensible Markup Language (XML) as a solution.

As a means to design a customized language for document markup and content, XML has more than fulfilled its original purpose of enabling different classes of complex, multi-structured documents to be shared over the Internet or private networks among disparate applications. XML combines descriptive meta data in the form of tags and actual data into a single entity, which means XML documents are essentially self describing. This is a unique and extremely powerful feature that provides many advantages, especially when compared to HTML. This is illustrated by the following example.

Lets assume you are searching for a book by a particular author at an online bookseller. After typing in the author's name, a Web page is returned containing perhaps 2,000 lines of HTML. Somewhere on that page are a list of titles by that author. Looking at the HTML displayed on your computer screen, you can tell which are the book titles because, as humans, we're used to recognizing patterns and formats. Unfortunately, a computer is not so intuitive.

To find those book titles, a special program would have to be written that could identify the 10 or so lines of useful data (titles) in the 2,000 lines of HTML code. In contrast, if search results were returned in XML, the useful data would be identified by tags such as "title," "author," publisher," etc.

Obviously, writing a computer program that looked for those tags would be fairly straightforward. What's more, that program could be re-used where data conformed to the same Document Type Descriptor (DTD)-a description of what tags are in a document and their order. If the structure of the search result changes, it would not be difficult to detect those changes and adapt the program to accommodate them.

XML's defining characteristics-a hierarchical structure and self-contained meta data-provide many valuable advantages to Web developers.

While HTML is still the industry standard, the use of XML in Web site construction is increasing exponentially each year. As the speed, ease of use, flexibility and cost-effectiveness of XML become more widely known, XML may well emerge as the de facto Web development language. Certainly, if you are about to or are in the process of building a major site that has to accommodate frequent changes, you would be wise to consider XML.

Excerpted with permission from an article by Dave Jakopac and Dave Hurst, vice presidents of Lisle Technology Partners, a technology consulting firm.