Using SGML to Leapfrog HTML

The creators of the original standards and their successor organization, the W3C, scrambled to catch up for a while. “Netscape extensions” provided designers with controls that the early versions of HTML had lacked and fueled the phenomenal growth of Netscape. Only recently has the W3C caught up to the browser developers and cut them off at the pass, with the next set of powerful standards. Cascading Style Sheets was the first blow. CSS made it possible for designers to declare their formatting intentions for a document without having to cook up a tortured mix of tags and graphics. CSS frees tags from the burden of carrying formatting information and permits them to carry content information once again.

XML emphasizes the importance of that content information by making it possible for designers to create and manage their own sets of tags. Designers can apply this in concert with CSS to create tags that produce formatting if they like, but the main emphasis is on managing content, including hypertext links, which received enhanced specifications. XML arose from the concerns of the SGML working group at the W3C, which felt that HTML was heading in the wrong direction. Rather than propose a replacement, they proposed ways to allow developers to extend HTML, maintaining backward compatibility while moving forward with more manageable techniques. XML provides a subset of SGML functionality rather than just a set of tags that use SGML syntax. It remains a simplification (and there is some grumbling from SGML users about how gross a simplification it may be), but it promises to restore the initial promise of HTML, adding a little more complexity in an attempt to simplify the complicated mess that determined the current state of Web page creation.

In this book, we’ll take a close look at the tools XML provides and how developers can apply them to common tasks. HTML developers should find much of the information familiar, although much of the content (creating DTDs, for instance) will be fairly alien. This book isn’t targeted at SGML developers, but readers familiar with SGML should find many familiar concepts integrated with the wilder world of the Web. Although the book focuses on creating documents with XML, we’ll also cover techniques for managing XML and integrating it with other Web technologies. XML may seem abstract at first, but its practical implications should become more evident as you proceed through the book and try the examples. We’ll see how XML documents can be used as databases even though they are very unlike the previous generations of strictly hierarchical or tabular structures, and we’ll explore the new architectures XML makes possible.