Despite its modest title, this book is one of the most useful books on Extensible Markup Language (XML) that I have come across. The book, a relatively short text in comparison with most XML references, manages to provide effective explanations of the core features of XML, as well as relevant references to applications and more advanced features.

The book is made up of four parts. Part 1 introduces the essential core of XML, Part 2 describes a selection of XML technologies used in narrative documents, Part 3 addresses data-centric aspects such as tools and application programming interfaces (APIs) for XML processing, and Part 4 is a quick reference, covering details of the core topics presented in the previous parts. In this second edition, several chapters have been upgraded to reflect the latest versions of various specifications, and chapters on schema languages have been added.

The introductory chapter does its best to dispel some common myths about XML. XML is introduced from an application point of view. The authors relate it to issues with which the practitioner can identify, such as cross-platform portability and the need for long-term data formats. Although the book is more suitable for practitioners, students and beginners might be able to build a good conceptual road map of XML technology by reading Part 1. Chapter 1 is particularly effective in bringing order to the apparently chaotic world of XML.

Chapters 2 and 3 introduce elements of XML syntax, defining well-formedness and validity criteria respectively. Validity is explained in terms of document type definitions (DTDs). Although it is common practice, explaining XML syntax in terms of DTDs always seems somewhat unnatural. A conceptual breakdown is likely to occur when the reader, newly introduced to the basics of XML, and starting to get used to its syntax, encounters a DTD. The problem is that DTDs have a totally different syntax from XML. This means that the reader needs to cope with DTD syntax while attempting to gain a deeper understanding of how XML syntax can be shaped by it.

Unfortunately, there seems to be no alternative to using DTDs to introduce the notion of valid XML. The schema language, itself an XML application, is probably too complex to be suitable for introductory chapters. However, the authors do make an attempt to balance the abstract descriptions of XML syntax with software that enables the reader to parse and validate documents, and to test the examples presented in the book. No software is included with the book, but the examples use the Apache Group’s J-Xerxes parser, which is easily obtainable free software. Java and J-Xerxes are also used in Part 3 to illustrate the document object model (DOM) and the simple API for XML (SAX).

A less satisfying aspect of the book is the fact that sometimes, mainly in Parts 2 and 3, the authors refer to topics that are only covered later in the book, and even sometimes to topics outside its scope. The chapter on “Namespaces,” for example, refers to the resource des cription framework (RDF) and the Dublin Core. Readers of an introductory chapter are usually not familiar with these topics. However, neither RDF nor the Dublin Core is discussed in the book, except for brief descriptions in chapter 7. To be fair, the presentation does not necessarily rest on the assumption that the reader is familiar with those external references. However, these inconsistencies are potentially confusing for the nonexpert, and unnecessary for the expert reader.

The chapters on presentation layout are somewhat weak. The coverage of Extensible Stylesheet Language Transformations (XSLT) is quite detailed, but the book does not provide enough coverage of core presentation layout technologies. Apart from a useful section on “Choosing Between CSS and XSL-FO,” the chapters on cascading style sheets (CSS) and XSL formatting objects (XSL-FO) are rather superficial. Detailed syntax references for CSS and XSL-FO are also missing from Part 4.

In spite of these minor deficiencies, I would recommend this book to anyone with an interest in XML. As a reference, it suits the needs of two main groups of readers. Those who have had some exposure to XML technology, but who are not experts, will find Parts 1, 2, and 3 most useful. Those with greater familiarity with XML will find the detailed reference in Part 4 to be a valuable resource. Furthermore, the book’s layout, the practice it follows of intercalating small code fragments and explanations, and the detailed index will benefit readers in intermediary stages.

XML has become a buzzword in the computer industry in recent years, but few people have a real understanding of what XML technology is, or how it might develop. Computer professionals wishing to discover what the hype is all about need a concise and unpretentious book that explains XML concepts, with reference to those familiar practical problems which motivated the appearance of XML in the first place. This book meets that need.