Introduction

veryone interested in the future of the Web must be curious---and pretty uncertain---about what may be the outcome of the HTML case.  Browser wars and incompatible extensions tearing apart the language are not only bad by themselves, they're a sure sign that something's going wrong with HTML in the first place.  It may sound like heresy that the tongue spoken by millions of Web pages is approaching the end of its useful life, but many serious observers cannot suppress exactly that feeling.

If we strip away for a moment the innumerable struts, crutches, and sophisticated gizmos that make the HTML golem walk and speak and look alive, what we'll see will be a pretty simple (not to say primitive) markup language designed for basic documents of a quite predictable structure.  Just headers, paragraphs, block quotations, and the good old ADDRESS at the end.  Does this sound like a model structure for the whole world of information out there?

Of course, now HTML has tables and fonts and all that.  Indeed, visual HTML extensions (or inline images, as the last resort) enable you to emulate any document structure---that is, make the document look as if it is properly structured.  But as a result, the internal structure of the text will inevitably become illogical, cumbersome, presentation-oriented (and with images, the text may cease to be text at all).  This is very likely to prevent reusing the document in the future; it becomes difficult even to convert it into another visually oriented format, not to mention isolate its logical elements.

Fortunately, there's a new important language designed to address this issue.  XML (eXtensible Markup Language) is a simple and compact subset of SGML designed specifically for use on the Internet in the way that HTML is currently used.  This new project of W3C is gaining momentum at a surprising rate, and everybody seriously concerned with HTML may want to check it out.  Maybe someday, you'll find yourself saying, "Back in those days when everyone was using HTML..."

Chapter Table of Contents

• Introduction
• The Premises of XML
• Well-Formed XML Documents
• XML DTDs and Valid XML Documents
  • Accessing the DTD
  • Element Declarations
  • Entity Declarations
• Linking Capabilities of XML
• The Prospects of XML
• Summary