Prentice Hall PTR
Upper Saddle River, New Jersey
1999
This definitive resource book is a detailed reference to the Extensible Markup Language (XML). It provides background information about XML, descriptions of its purpose and function, and numerous examples of its use.
The senior author of this book was the creator of SGML, the international standard for structured information on the internet. Both HTML and XML are based on SGML. As described by the authors, XML provides ordinary people with a way to "craft their own data, the ability to shape and control data." They point out that while data was once a mysterious blob, with XML it can now become something people can read and author, because it is text. They say their goal in developing XML was to produce a very simple markup language with as few abstractions as possible.
The authors pose an interesting question: how can they be so confident in promoting XML when it is so new? Their answer is that it is because the central ideas in XML have been extensively tested and that it is based on SGML, an established markup language; it is, they point out, a streamlined subset of the original SGML markup language. In fact, both XML and the more familiar HTML are based on SGML. So, if we accept the concept that a markup language (a term that author Charles Goldfarb coined in 1970)is the best approach to cross-platform web page delivery, then a markup language that can be extended is even better.
After a discussion of SGML and HTML, the book describes such XML issues as data management and data storage. Instead of creating formatted renditions (as in word processing), XML's presentation-oriented publishing capabilities create unformatted abstractions; that is, the document file captures what is in the document, not how it is supposed to look. To do that, XML creates a stylesheet, which is a set of commands that tell a program how to format a document.
The authors also point out that XML's documents can be interactive when delivered in electronic media. They describe XML as message-oriented middleware which acts like an interpreter, a data integrator. As they put it: ". . . documents are chiefly generated by programs for other programs to read." Instead of writing specialized programs (which they refer to as "clients") to access particular databases, XML breaks the old two-tier client/server model by introducing a third tier, a "middle" tier that does all the talking to the data sources and sends messages (in XML) to the client.
The authors describe XML as a better model for doing business on the web, and they provide some examples of how it could be used for that purpose. They depend on extensive examples to demonstrate the various applications of XML. That is one of the best aspects of this book: it introduces XML's various - and seemingly complex - options through easier-to-understand examples. It makes the book easy to read, although it might make it harder to use as a reference. Later chapters introduce basic XML concepts using named conventions that are easier to reference.
The authors clearly believe the best way to understand the difference between XML and HTML is to provide an example of the same document marked up with each. Below is the example they provide:
Both of these examples will appear the same on today's browsers, but the authors describe the XML version as smart data, containing information about the data (product, model, dealer, price) beyond its formatting.
The 639-page revised edition also includes a CD-ROM with useful XML tools and a collection of free, no-time-limit XML-based software. The CD-ROM includes parsers and engines, editing and composition tools, and information for XML development. It also includes a collection of useful resources and internet locations where you can find additional XML information.
