Sams Teach Yourself HTML 4 in 24 Hours

By Dick Oliver

• Table of Contents
  • Copyright
  • About the Author
  • Acknowledgments
  • Tell Us What You Think!
  • Put Your HTML Page Online Today
  • I. Your First Web Page
  • Hour 1. Understanding HTML and XML
  • Hour 2. Create a Web Page Right Now
  • Hour 3. Linking to Other Web Pages
  • Hour 4. Publishing Your HTML Pages
  • II. Web Page Text
  • Hour 5. Text Alignment and Lists
  • Hour 6. Text Formatting and Font Control
  • Hour 7. Email Links and Links Within a Page
  • Hour 8. Creating HTML Forms
  • III. Web Page Graphics
  • Hour 9. Creating Your Own Web Page Graphics
  • Hour 10. Putting Graphics on a Web Page
  • Hour 11. Custom Backgrounds and Colors
  • Hour 12. Creating Animated Graphics
  • IV. Web Page Design
  • Hour 13. Page Design and Layout
  • Hour 14. Graphical Links and Imagemaps
  • Hour 15. Advanced Layout with Tables
  • Hour 16. Using Style Sheets
  • V. Dynamic Web Pages
  • Hour 17. Embedding Multimedia in Web Pages
  • Hour 18. Interactive Pages with Applets and ActiveX
  • Hour 19. Web Page Scripting for Non-Programmers
  • Hour 20. Setting Pages in Motion with Dynamic HTML
  • VI. Building a Web Site
  • Hour 21. Multipage Layout with Frames
  • Hour 22. Organizing and Managing a Web Site
  • Hour 23. Helping People Find Your Web Pages
  • Hour 24. Planning for the Future of HTML
    • HTML Beyond the Web
    • From Calculators to Communicators
    • HTML as the New User Interface
    • The Digital Media Revolution
    • XML: Unity in Diversity
    • XHTML, the New HTML
    • HTML Applications of the Future
    • What You Can Do Today to Be Ready for Tomorrow
    • Summary
    • Q&A
    • Workshop
  • VII. Appendixes
  • A. Readers' Most Frequently Asked Questions
  • B. HTML Learning Resources on the Internet
  • C. Complete HTML 4 Quick Reference
  • D. HTML Character Entities

XML: Unity in Diversity

So far in this hour I've noted how HTML is in the right place at the right time to enable several key changes in business and interpersonal communication. As the people and companies of the world become more connected and dependent upon one another, HTML's capability to make all information technology easier to use and less constrained by geography seems almost magical.

Even more magically, HTML has enabled an explosion of new media formats and incompatible file types, while at the same time providing the first truly universal format for exchanging all types of information. The limitations of the HTML language itself have stood in the way of it truly fulfilling this important role, however. To address these limitations, the World Wide Web Consortium has created a new language called XML, or eXtensible Markup Language.

Before you can understand what XML is and why it may be a key to the future of computer communication, you first have to meet its mother. Her name is SGML, or Standard General Markup Language. She is a venerable, time-worn standard for describing other mark-up languages. HTML is just one of many languages that can be defined in SGML. Others include specialized languages for library indexing, print publications management, mathematical formulas, molecular chemistry, and so on. Although no one SGML browser can render all these specialized document types, any SGML browser can read the document type definition (DTD) and figure out how to render those elements of the document type that it understands while ignoring the rest.

It would be ideal if Web browsers could read any SGML document type instead of being limited to HTML documents. The problem with this idea is that SGML is so complex and powerful that it can be very difficult to learn and implement. If this book were about SGML, the title would be something like Sams Teach Yourself SGML in a Year and a Half.

XML was created to bridge the gap between HTML, which is easy to learn but kinda wimpy, and SGML, which gives you God-like powers but may require several reincarnations to master. Like SGML, XML allows you to define your own special-purpose tags and implement complex link relationships between documents. Like HTML, XML is simple enough to learn fairly quickly because it avoids all the more esoteric (and least commonly used) aspects of SGML.

XML is a general-purpose language, which includes all the HTML tags but also allows specialized extensions of the language to be easily defined without losing compatibility with the core language. XML standardizes the format of the most common types of information while freely allowing unlimited special cases for proprietary formats and new technology. This means that you can both ensure complete compatibility between the widest variety of software and easily develop unique information formats to meet your individual needs.

The ability to extend HTML pages with custom data types is far more than a way to embed a nifty movie or virtual reality scene into your Web page. To show how much more, the next section of this hour highlights some of the most exciting up-and-coming uses of XHTML and XML.

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