XML in an Instant:
A Non-geeky Introduction

Charles F. Goldfarb

Charles F. Goldfarb is the father of XML technology. He coined the term "markup language" and invented SGML, the mother tongue of both HTML and XML. He edits Prentice-Hall's Definitive XML Series and is co-author of The XML Handbook™, Fifth Edition.

By now, everyone familiar with the World Wide Web knows that it is undergoing a radical change that is introducing wonderful services for users and amazing new opportunities for Web site developers and businesses.

HTML—the HyperText Markup Language—made the Web the world's library. Now its sibling, XML—the Extensible Markup Language—is making the Web the world's commercial and financial hub.

In the process, the Web is becoming much more than a static library. Increasingly, users are accessing the Web for "Web pages" that aren't actually on the shelves. Instead, the pages are generated dynamically from information available to the Web server. That information can come from data bases on the Web server, from the site owner's enterprise data bases, or even from other Web sites.

And that dynamic information needn't be served up raw. It can be analyzed, extracted, sorted, styled, and customized to create a personalized Web experience for the end-user. To coin a phrase, Web pages are evolving into Web services.

For this kind of power and flexibility, XML is the markup language of choice. You can see why by comparing XML and HTML. Both are based on SGML—the International Standard for structured information—but look at the difference:

In HTML:

<p>P266 Laptop
<br>Friendly Computer Shop
<br>$1438

In XML:

<product>
<model>P266 Laptop</model>
<dealer>Friendly Computer Shop</dealer>
<price>$1438</price>
</product>

Both of these may look the same in your browser, but the XML data is smart data. HTML tells how the data should look, but XML tells you what it means.

With XML, your browser knows there is a product, and it knows the model, dealer, and price. From a group of these it can show you the cheapest product or closest dealer without going back to the server.

Unlike HTML, with XML you create your own tags, so they describe exactly what you need to know. Because of that, your client-side applications can access data sources anywhere on the Web, in any format. New "middle-tier" servers sit between the data sources and the client, translating everything into your own task-specific XML.

But XML data isn't just smart data, it's also a smart document. That means when you display the information, the model name can be a different font from the dealer name, and the lowest price can be highlighted in green. Unlike HTML, where text is just text to be rendered in a uniform way, with XML text is smart, so it can control the rendition.

And you don't have to decide whether your information is data or documents; in XML, it is always both at once. You can do data processing or document processing or both at the same time.

With that kind of flexibility, it's no wonder that we're starting to see a new Web of smart, structured information. It's a "Semantic Web" in which computers understand the meaning of the data they share. Your broker sends your account data to Quicken using XML. Your imaging software keeps its templates in XML. Everything from math to multimedia, chemistry to commerce, wireless to Web services, is using XML or is preparing to start.

You should be too!


To Charles F. Goldfarb's All the XML Books in Print ...

To The XML Handbook™, Fifth Edition.


Copyright ©2004 Charles F. Goldfarb. All rights reserved. This information cannot be used or cited for any commercial purpose, although links to it are welcome.