XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (3 page)

Credits

Director of Acquisitions

Jim Minatel

Development Editor

Maureen Spears

Technical Editor

Sam Judson

Production Editor

Angela Smith

Copy Editor

Foxxe Editorial Services

Editorial Manager

Mary Beth Wakefield

Production Manager

Tim Tate

Vice President and Executive Group Publisher

Richard Swadley

Vice President and Executive Publisher

Joseph B. Wikert

Project Coordinator, Cover

Lynsey Stanford

Proofreader

Nancy Carrasco

Indexer

Robert Swanson

Acknowledgments

There are two groups of people I must thank: those who contributed to the book, and those who supported me in writing it.

In the first group, I am indebted to readers of previous editions who have pointed out my errors, and have told me what they liked and didn't like. I hope readers of this edition will do the same. Also to the (by now numerous) reviewers and editors engaged first by the original Wrox team in the UK, and more recently by their successors in Wiley, who have done so much of the legwork of testing example code and finding continuity errors, not to mention handling the unseen production processes that turn a heap of word-processed text into a finished book. Then my colleagues on the working groups, who provided the subject matter for me to write about, and those who taught me how to use the language—if you find a programming pearl that you particularly like in this book, the chances are I stole the idea from someone. James Clark in particular, who invented the XSLT language and showed me how it worked.

In the second group, I must once again acknowledge the patience of my family, who sighed resignedly when I suggested the prospect of retreating to my study for half a year to produce a new revision, and the generosity of my past employers who provided the time to get the project off the ground in the first place.

Introduction

This book, as the title implies, is primarily a practical reference book for professional XSLT developers. It assumes no previous knowledge of the language, and many developers have used it as their first introduction to XSLT; however, it is not structured as a tutorial, and there are other books on XSLT that provide a gentler approach for beginners.

Who This Book Is For

The book does assume a basic knowledge of XML, HTML, and the architecture of the Web, and it is written for experienced programmers. There's no assumption that you know any particular language such as Java or Visual Basic, just that you recognize the concepts that all programming languages have in common.

I have tried to make the book suitable both for XSLT 1.0 users upgrading to XSLT 2.0, and for newcomers to XSLT. This is easier to do in a reference book, of course, than a tutorial. I have also tried to make the book equally suitable whether you work in the Java or .NET world.

As befits a reference book, a key aim is that the coverage should be comprehensive and authoritative. It is designed to give you all the details, not just an overview of the 20 percent of the language that most people use 80 percent of the time. It's designed so that you will keep coming back to the book whenever you encounter new and challenging programming tasks, not as a book that you skim quickly and then leave on the shelf. If you like detail, you will enjoy this book; if not, you probably won't.

But as well as giving the detail, this book aims to explain the concepts, in some depth. It's therefore a book for people who not only want to use the language but who also want to understand it at a deep level. Many readers have written to me saying that they particularly appreciate these insights into the language, and it's my sincere hope that after reading it, you will not only be a more productive XSLT programmer, but also a more knowledgeable software engineer.

What This Book Covers

The book aims to tell you everything you need to know about the XSLT 2.0 language. It gives equal weight to the things that are new in XSLT 2.0 and the things that were already present in version 1.0. The book is about the language, not about specific products. However, there are appendices about Saxon (my own implementation of XSLT 2.0), about the Altova XSLT 2.0 implementation, and about the Java and Microsoft APIs for controlling XSLT transformations, which will no doubt be upgraded to handle XSLT 2.0 as well as 1.0. A third XSLT 2.0 processor, Gestalt, was released shortly before we went to press, too late for us describe it in any detail. But the experience of XSLT 1.0 is that there has been a very high level of interoperability between different XSLT processors, and if you can use one of them, then you can use them all.

In the previous edition we split XSLT 2.0 and XPath 2.0 into separate volumes. The idea was that some readers might be interested in XPath alone. However, many bought the XSLT 2.0 book without its XPath companion and were left confused as a result; so this time, we've brought the material back together. The XPath reference information is in self-contained chapters, so it should still be accessible when you use XPath in contexts other than XSLT.

The book does not cover XSL Formatting Objects, a big subject in its own right. Nor does it cover XML Schemas in any detail. If you want to use these important technologies in conjunction with XSLT, there are other books that do them justice.

How This Book Is Structured

This book contains twenty chapters and eight appendixes (the last of which is a glossary) organized into four parts. The following section outlines what you can find in each part, chapter, and appendix.

Part I: Foundations

The first part of the book covers essential concepts. I recommend reading these before you start coding. If you ignore this advice, as most people do, then I suggest you read them when you get to that trough of despair when you find it impossible to make the language do anything but the most trivial tasks. XSLT is different from other languages, and to make it work for you, you need to understand how it was designed to be used.

Chapter 1: XSLT in Context

This chapter explains how XSLT fits into the big picture: how the language came into being and how it sits alongside other technologies. It also has a few simple coding examples to keep you alert.

Chapter 2: The XSLT Processing Model

This is about the architecture of an XSLT processor: the inputs, the outputs, and the data model. Understanding the data model is perhaps the most important thing that distinguishes an XSLT expert from an amateur; it may seem like information that you can't use immediately, but it's knowledge that will stop you from making a lot of stupid mistakes.

Chapter 3: Stylesheet Structure

XSLT development is about writing stylesheets, and this chapter takes a bird's-eye view of what stylesheets look like. It explains the key concepts of rule-based programming using templates, and explains how to undertake programming-in-the-large by structuring your application using modules and pipelines.

Chapter 4: Stylesheets and Schemas

A key innovation in XSLT 2.0 is that stylesheets can take advantage of knowledge about the structure of your input and output documents, provided in the form of an XML Schema. This chapter provides a quick overview of XML Schema to describe its impact on XSLT development. Not everyone uses schemas, and you can skip this chapter if you fall into that category.

Chapter 5: The Type System

XPath 2.0 and XSLT 2.0 offer strong typing as an alternative to the weak typing approach of the 1.0 languages. This means that you can declare the types of your variables, functions, and parameters, and use this information to get early warning of programming errors. This chapter explains the data types available and the mechanisms for creating user-defined types.

Part II: XSLT and XPath Reference

This section of the book contains reference material, organized in the hope that you can easily find what you need when you need it. It's not designed for sequential reading, though if you're like me, you might well want to leaf through the pages to discover what's there.

Chapter 6: XSLT Elements

This monster chapter lists all the XSLT elements you can use in a stylesheet, in alphabetical order, giving detailed rules for the syntax and semantics of each element, advice on usage, and examples. This is probably the part of the book you will use most frequently as you become an expert XSLT user. It's a “no stone unturned” approach, based on the belief that as a professional developer you need to know what happens when the going gets tough, not just when the wind is in your direction.

Chapter 7: XPath Fundamentals

This chapter explains the basics of XPath: the low-level constructs such as literals, variables, and function calls. It also explains the context rules, which describe how the evaluation of XPath expressions depends on the XSLT processing context in which they appear.

Chapter 8: XPath: Operators on Items

XPath offers the usual range of operators for performing arithmetic, boolean comparison, and the like. However, these don't always behave exactly as you would expect, so it's worth reading this chapter to see what's available and how it differs from the last language that you used.

Chapter 9: XPath: Path Expressions

Path expressions are what make XPath special; they enable you to navigate around the structure of an XML document. This chapter explains the syntax of path expressions, the 13 axes that you can use to locate the nodes that you need, and associated operators such as union, intersection, and difference.

Chapter 10: XPath: Sequence Expressions

Unlike XPath 1.0, in version 2.0 all values are sequences (singletons are just a special case). Some of the most important operators in XPath 2.0 are those that manipulate sequences, notably the
for
expression, which translates one sequence into another by applying a mapping.

Chapter 11: XPath: Type Expressions

The type system was explained in Chapter 5; this chapter explains the operations that you can use to take advantage of types. This includes the
cast
operation which is used to convert values from one type to another. A big part of this chapter is devoted to the detailed rules for how these conversions are done.

Chapter 12: XSLT Patterns

This chapter returns from XPath to a subject that's specific to XSLT. Patterns are used to define template rules, the essence of XSLT's rule-based programming approach. The reason for explaining them now is that the syntax and semantics of patterns depends strongly on the corresponding rules for XPath expressions.

Chapter 13: The Function Library

XPath 2.0 includes a library of functions that can be called from any XPath expression; XSLT 2.0 extends this with some additional functions that are available only when XPath is used within XSLT. The library has grown immensely since XPath 1.0. This chapter provides a single alphabetical reference for all these functions.

Chapter 14: Regular Expressions

Processing of text is an area where XSLT 2.0 and XPath 2.0 are much more powerful than version 1.0, and this is largely through the use of constructs that exploit regular expressions. If you're familiar with regexes from languages such as Perl, this chapter tells you how XPath regular expressions differ. If you're new to the subject, it explains it from first principles.

Chapter 15: Serialization

Serialization in XSLT means the ability to generate a textual XML document from the tree structure that's manipulated by a stylesheet. This isn't part of XSLT processing proper, so (following W3C's lead) we've separated it into its own chapter. You can control serialization from the stylesheet using an

declaration, but many products also allow you to control it directly via an API.

Part III: Exploitation

The final section of the book is advice and guidance on how to take advantage of XSLT to write real applications. It's intended to make you not just a competent XSLT coder, but a competent designer too. The best way of learning is by studying the work of others, so the emphasis here is on practical case studies.

Chapter 16: Extensibility

This chapter describes the “hooks” provided in the XSLT specification to allow vendors and users to plug in extra functionality. The way this works will vary from one implementation to another, so we can't cover all possibilities, but one important aspect that the chapter does cover is how to use such extensions and still keep your code portable.