Preface
XML
The Extensible Markup Language is a powerful document publishing and data interchange format. It was released in 1998 by the World Wide Web Consortium, to immediate and widespread acclaim. XML has a superficial resemblance to HTML, the established language of the Web, but information held in this format is self-describing – it can be extracted, manipulated and formatted to the requirements of any target audience, publishing medium or XML-enabled software application. XML should be of interest to HTML designers who need more flexibility to manage and customize their documents, to SGML users seeking advanced yet modestly priced applications, and to software developers requiring a flexible storage or interchange format that benefits from powerful, often freely available supporting tools.
This book
The XML Companion serves the programmer, analyst or consultant involved in the management, processing, transfer or publication of XML data and documents. Detailed study of the standard is supported by the inclusion of cross-referenced 'road maps' of the building blocks that comprise the standard, and an extensive glossary. Related standards for cataloguing, processing, linking and styling XML documents are also covered in detail.
The third edition
This is the third edition of The XML Companion. While the standard itself has not changed since its release in 1998, many important supporting standards have emerged, progressed, or been finalized and officially released. New editions are needed to keep up with this progress. But a significant issue that arises when writing a book on XML today is deciding what to leave out. Hundreds of XML-based standards have now been developed. A book several times the size of this one could be written, but it would not be practical to publish it, or indeed to carry it around. Apart from the core chapters on the XML standard itself, this book concentrates on related standards developed by the W3C, and on the two most popular applications of this technology (document publishing and data exchange).
Standards for navigating, describing, processing, transforming, presenting, resolving relative URL links, and linking XML data, previously described in their draft form (or too new to have been mentioned before), have now been completed and released. This includes XPath (November 1999), XML Schema (May 2001), SAX 2.0 (June 2000), DOM 2.0 (November 2000), XSLT (November 1999), XHTML 1.0 (January 2000), XML Base (June 2001) and XLink (June 2001). Another draft proposal for advanced XML linking has matured significantly: XPointer (September 2001). Finally, a proposal for merging XML structures has been announced: XML Inclusions (May 2001). Selected loosely-related standards, such as XHTML and CSS, are included because of their historical significance and widespread use, and because they form the basis of several other standards.
Despite the wealth of new material, very little from the previous edition has been omitted (the HTML 4.0 chapter has been replaced by one on XHTML, and the chapter on XSL has been dropped (see The XML Companion for a full description of this language)), so this book is larger than before. Yet it is hoped by the author that this book can still serve as a 'companion' for those who are constantly on the move.
Acknowledgements
Thanks to Michael Will for proofreading the first draft, to Viki Williams and Katherin Ekstrom at Pearson Education for steering this book to completion, and once again to Adobe for FrameMaker+SGML (which was used both in the preparation and publication of this book). Finally, thanks to those readers of the second edition who mailed corrections and suggestions.
Feedback
Comments and suggestions for a possible future edition are welcome. They should be sent to the author, who can be contacted at [email protected]. Updates, additions and corrections can be obtained from the author's Web page, located at www.bradley.co.uk, which also contains links to various XML- and SGML-related sites, and all the standards covered in this book.
Neil Bradley
October 2001