XML: The Hope and the Hype
The evolutionary dynamic of human communication technologies can be described simply as a battle against time and distance. Every innovation since before the advent of the printing press has increased the distance over which we communicate while decreasing the time it takes to communicate. And with every innovation, the volume of communications increase and types of communications diversified.
Today, the Internet facilitates human to human communication between geographically distant "correspondents" nearly instantaneously. The volume of communications defies imagining and the types of communications range from a simple e-mail to data transfer to application sharing. What you see on the screen of your PC, laptop, palm pilot or wireless is only the tip of a technological iceberg that makes such human to human communications possible.
In between you and the person at the other end of the cyberstream is a vast network that demands sophisticated "computer to computer" communications. A technological innovation that is changing the way computers communicate is XML (Extensible Markup Language).
What is XML?
"In brief, XML offers a widely adopted standard way of representing text and data in a format that can be processed without much human or machine intelligence. Information formatted in XML can be exchanged across platforms, languages, and applications, and can be used with a wide range of development tools and utilities."--XML - The Site
XML permits users to create tags that "narratively" describe and structure data. In a Scientific American article (May, 1999), Jon Bosak and Tim Gray write that humans can discern at a glance whether "data" is a shopping list, a magazine article or a bank statement, computers need some help. Bosak and Gray, both intimately involved in the development of XML, write, "Computers, of course, are not that smart; they need to be told exactly what things are, how they are related and how to deal with them." XML provides computers with the "hints" humans take for granted.
What's the difference between XML, HTML and SGML?
As their acronyms suggest, XML, SGML and HTML are related. All three are markup languages. HTML (Hypertext Markup Language) makes use of tags and the tags look similar to XML. Both HTML and XML are suited for the Web. The fundamental difference between the two is that HTML tags define how elements are displayed. XML tags define what data means.
In computational terms, XML is closer to SGML. Indeed, XML is an application profile, or subset, of SGML (Standard Generalized Markup Language). Both provide "arbitrary" structures, i.e., tags may be user-defined. And both describe what data signifies not what it looks like. Norman Walsh, in an article published on the XML.com site, defines the difference between the two. "Full SGML systems solve large, complex problems that justify their expense. Viewing structured documents sent over the web rarely carries such justification." XML, a sort of SGML-lite, "is being designed to deliver structured content over the web," Walsh writes.
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