A Guide to XML Transormations
Author: James Robert Gardner,John Robert Gardner,Zarella L. Rendon
Publisher: Prentice Hall Professional
Preface You've heard of XML; your manager wants you to use it in your applications. Now what? You've used HTML, and you know what a tag is; you know that it is somehow related to XML. You may even know what XML is and what it does. What you may not know is that, while XML identifies and adds structure to the content of a document, it does not tell you anything about how to process that content, or how to do anything useful with it beyond storage. This is good news, because this means your content can be used for many different purposes. There are many things you can use to process content once it is marked up using XML. However, we have chosen to talk about the only standard application that allows you to do many different things with it. With XSLT, you can add style to XML, convert it to other XML, or simply chop it up and regenerate it in a different form. XSLT is the power behind the throne of XML. It assures that every level of every piece of XML data is accessible and reusable across platforms and forward in time. It is not an exaggeration to say that XSLT and its companion XPath are the very glue and mortar that hold together and build the endlessly varying applications of markup data for any industry, academy, or individual. XSLT is the fastest cure for the fear of having obsolescence in a data or information architecture design. XSLT is easy to use. In fact, XSLT itself is XML. XSLT "speaks the language," or the syntax, of XML with a powerful vocabulary of programming-like features that are nonetheless easy to use, learn, and understand. XSLT attempts to be a bridge to nonprogrammers, bringing the easily understood syntax of XML together with a powerful scripting mechanism and simple pathing approach to document navigation. It is our belief-and our approach in writing this book-that both the experienced programmer and the newly trained markup technologist can become more comfortable with the potent set of tools for preserving, augmenting, updating, and delivering XML data-whether it's on the Web or your corporation's intranet or B2B. If you are constantly wishing you had just a little more control over your information, this book will deliver that-and much more. In fact, by the end of the first chapter, you will be able to perform basic conversions from XML documents to HTML that will display in any Web browser. Subsequent chapters build upon and enhance that base of knowledge, matching examples with detailed explanations and providing focus upon commonly misunderstood areas. When you read this book, have your computer handy. Take the time to load up one of the XSLT processors and work along as you read. Learning by doing is always best, especially with XSLT and XPath. Chapter 13 will show you how to install the software included on the CD. Each example in the book is found on the CD in the examples directory, organized by chapter. XSLT is rewarding and creative to use. Be prepared to enjoy this learning experience. You will be surprised by how quickly productive use of this technology increases. Why Should You Use XSLT? Browsers display HTML, not general XML tags. You have to do something with the XML once you have it. Can you print with XML? Can you send XML to the Web? Can you browse XML? Yes, but not alone. XSLT lets you convert XML to HTML, other types of XML or just plain text. With a little creativity, and the proper knowledge of XSLT, you can generate practically any form of output from XML. XSLT provides quick, easy solutions to all XML transformation issues. However, the designers of XSLT did not intend for you to use the specification without additional help. "This book, along with the proper tools, is what is required for XML to succeed with the average business application." —Sharon Adler, Co-Chair W3C XSL Working Group The latest version of XSLT (for which this book is written) is 1.0. There are many additional features that are being considered by the W3C XSL committee, and version 2.0 promises to add some of these new features, as well as provide support for XML Schema, XML Query, and others. Who Is This Book For? This book is for anyone who works with electronic data and wants to enable XML transformations without a difficult programming language learning curve. If you are comfortable working with SGML, XML, or even HTML, you will benefit greatly from the common markup syntax. Some people may find XSLT difficult because it is not a procedural programming language. Most programming languages have a very structured, concise syntax. The syntax of XSLT is XML and is designed to be human readable and easily understandable. You must have some knowledge of markup before using XSLT. Some people may find XSLT difficult to use because it does not provide solutions to every transformation situation. For example, you cannot use XSLT to convert text to XML. There are situations when additional processing may be required. However, for most of your day-to-day XML transformations, XSLT is the tool of choice. Organization The book is organized to build a base of knowledge that will be added to chapter by chapter. Basic XSLT concepts and a brief overview of XML are covered in Chapter 1. The remainder of the chapters add functionality as required when creating stylesheets. The more complex the problem, the later it is covered. Chapter 1 provides everything you need to know about XML and XSLT in a nutshell. This chapter gives a good overview with minimum syntax, and can be used by people at any level of markup experience as a review or for general information. Chapter 2 covers stylesheet concepts that are crucial to understanding XSLT, as well as general stylesheet terminology. Chapter 3 adds more concepts, a little more explanation and usage, and an in-depth study of templates to the basics covered in Chapters 1 and 2. Chapter 4 defines and explains XPath expressions and patterns. Chapter 5 covers XPath functions, which are crucial to using most of the elements in XSLT. Chapter 6 walks through the creation of new XML elements and attributes using several different methods. Chapter 7 discusses the use of multiple stylesheets by including and importing them, as well as a discussion on template priority. Chapter 8 shows how to work with variables and parameters. Chapter 9 covers anything that is in some way iterative or conditional, as well as the utilities required to copy XML from the input to the output. Chapter 10 details the options for controlling output types, as well as stripping and preserving whitespace, and generating error messages. Chapter 11 covers XSLT functions and their related elements, including importing external XML documents with the document() function, and using keys with. Chapter 12 discusses extensions, processors, and Java, as well as three "commercial" XSLT processors. Chapter 13 describes three "freeware" processors: Xalan, Saxon, and XT, along with installation instructions and extension implementations. There are three appendices that cover a variety of topics and case studies, as well as contributed material. Versions This book is written according to XSL Transformations (XSLT) Version 1.0, XML Path Language (XPath) Version 1.0, and Extensible Markup Language (XML) 1.0. Additional reference material came from Namespaces in XML REC-xml-names-19990114. The version of James Clarks' XT used for the tests in this book is 19991105. The version of Michael Kay's Saxon used is 6.2.2.