XML: The Annotated Specification
by Bob DuCharme
368 pages, Prentice Hall

The name of the author of XML: The Annotated Specification may sound familiar. Some of you may have heard of him because of his contributions in the XML industry. For others it's probably because you've just seen his name on the cover of this magazine - Bob is writing the Standar Watch column. This book is an excellent sample of Bob's writing style and his ability to simplify the concepts introduced by a complex technology. I've never gone through the complete XML specification; however, like other language specifications, it's not for the average reader. I think Charles Goldfarb puts it succinctly in his foreword to the book when he describes the spec's terseness: "For earth people - even for most programmers - it's a daunting read indeed!"

Nevertheless, The Annotated Specification is clear and at the same time objective in its coverage of the XML spec. It is what it says it is - a specification book. It simplifies and clarifies the specification using pertinent examples, sidebars, tips and reviews of complex topics. It serves as a general reference for the XML language and a guide to the specification. The author goes through the specification line by line and then expands on each concept by offering insight into why the guideline/definition was created, what it means and how it's to be used.

This book isn't meant for readers who are trying to write XML applications or learning the XML language and its relationship to other technologies such as Java. It doesn't cover applications of XML in the industry, XML tools, and so on. That's not its purpose. The book is targeted to advanced readers who want to understand the reasoning behind the XML language and its pure definition. If you've never had a hankering to read the specification, then you probably won't get much out of this book.

The first section of the book, "Annotation Specification," consists of a couple of chapters that introduce the book and the XML specification. I believe these chapters will be useful to readers who aren't interested primarily in the specification. The information here may have been garnered from other resources, but may not be available elsewhere in such a comprehensive form. The author starts with the reasoning behind the birth of XML. He discusses XML in relation to HTML and SGML and what roles these technologies play in computing. This introductory chapter has nothing to do with the specification itself, but will be of use to most readers. Many of the concepts and XML components such as XSL, XLink and Xpointer are covered along with XML's relationship to browsers and scripting. The author ends the chapter with a brief description of the purpose of the specification and the additional information that this book has to offer.

Chapter 2 provides a preface to the W3C XML specification, and gives pointers on where readers can pick up the specification, its versioning, notation and syntax.

The next section of the book introduces the XML specification. The origin, goals and terminology of the specification are described in Chapter 1. One of the most useful features in this book becomes apparent here as the author takes each line of the specification and clarifies words that may be ambiguous. He clearly sets the context for the terms and gives the reasoning behind them.

An example is the author's explanation of what "parsed data" means in the context of the specification. Parsed data isn't data that has been parsed, but data for the XML processor (defined in the specification's next paragraph) to parse. Earlier drafts of the spec used the terms text and binary rather than parsed and unparsed.

These types of explanations are invaluable for eliminating confusion and ambiguity typically associated with language specifications.

Chapters 2-4 go over the main body of the specification and the XML language. XML documents, their components, DTDs, logical structures and their elements and attributes are covered in Chapters 2 and 3. Chapter 4 discusses physical structures, including entities, and introduces XML processors.

Chapters 5 and 6 focus on XML processing. Chapter 5 discusses validating and nonvalidating processors and their use. Chapter 6 elaborates the formal grammar rules for processing XML documents.

The remainder of the book comprises six appendices that provide further sources of information and explanations on related topics. A concise glossary for the terms used in the text is also provided.

A "specification" book isn't something that most folks read cover to cover and I'm no exception. However, it's a great reference to have when you need to know the meaning of various terms and concepts.