beginning xml 4th edition

free ebook for IT beginner focus xml programming

Beginning XML

4th Edition

David Hunter, Jeff Rafter, Joe Fawcett, Eric van der Vlist, Danny Ayers, Jon Duckett, Andrew Watt, and Linda McKinnon

Beginning XML

4th Edition

Beginning XML

4th Edition

David Hunter, Jeff Rafter, Joe Fawcett, Eric van der Vlist, Danny Ayers, Jon Duckett, Andrew Watt, and Linda McKinnon

Copyright © 2007 by Wiley Publishing, Inc., Indianapolis, Indiana

Published simultaneously in Canada

ISBN: 978-0-470-11487-2

Manufactured in the United States of America

10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data:

Beginning XML / David Hunter [et al.] 4th ed

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trade-Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available

in electronic books

I would like to thank God, for continuing to give me opportunities to do what I love; my church family, for giving me more support than I deserve; and Andrea, for giving me more support than anyone deserves

I would also like to thank the editors, for their constant help Their dedication to the quality of this book was a major factor in its success.

—David

To Ali and Jude, for their loving patience.

—Jeff

To my two brothers, Peter and Stephen, who have both helped me in my life

and career in their own ways, many thanks.

About the Authors

David Hunteris a Senior Technical Consultant for CGI, a full-service IT and business process servicespartner Providing technical leadership and guidance for solving his clients’ business problems, he is ajack-of-all-trades and master of some With a career that has included design, development, support,training, writing, and other roles, he has had extensive experience building scalable, reliable, enterprise-class applications David loves to peek under the hood at any new technology that comes his way, andwhen one catches his fancy, he really gets his hands dirty He loves nothing more than sharing thesetechnologies with others

Jeff Rafteris an independent consultant based in Redlands, California His focus is on emerging nology and web standards, including XML and validation He currently works with Baobab HealthPartnership with a focus on improving world health

tech-Joe Fawcett(http://joe.fawcett.name) started programming in the 1970s and worked briefly in ITwhen leaving full-time education He then pursued a more checkered career before returning to softwaredevelopment in 1994 In 2003 he was awarded the title of Microsoft Most Valuable Professional in XMLfor community contributions and technical expertise; he has subsequently been re-awarded every yearsince Joe currently works in London and is head of software development for FTC Kaplan Ltd., a lead-ing international provider of accountancy and business training

Eric van der Vlistis an independent consultant and trainer His domains of expertise include web opment and XML technologies He is the creator and main editor of XMLfr.org, the main site dedicated

devel-to XML technologies in French, the lead author of Professional Web 2.0 Programming, the author of the O’Reilly animal books XML Schema and RELAX NG and a member or the ISO DSDL (http://dsdl.org)working group focused on XML schema languages He is based in Paris and can be reached at

vdv@dyomedea.com, or meet him at one of the many conferences where he presents his projects

Danny Ayersis a freelance developer and consultant specializing in cutting-edge web technologies His blog (http://dannyayers.com) tends to feature material relating to the Semantic Web and/or cat photos

Linda McKinnonhas more than 10 years of experience as a successful trainer and network engineer,assisting both private and public enterprises in network architecture design, implementation, systemadministration, and RFP procurement She is a renowned mentor and has published numerous Linuxstudy guides for Wiley Press and Gearhead Press

Quality Control Technician

Proofreading

Aptara

Indexing

Broccoli Information Management

Anniversary Logo Design

Richard Pacifico

This book would not have been possible without the work of the many developers dedicated to ing the Web through standards We would also like to thank the countless contributors to mailing lists,IRC channels, forums, and friends that have helped us through the difficult corners of the specificationsand technologies presented in this book

improv-Thanks to Nicholas C Zakas for his ideas and assistance in implementing the AutoSuggest Control Manythanks to Phillip Pearson, who runs TopicExchange.com He provided much-needed technical supportthat otherwise would have meant rewriting most of Chapter 14 We would also like to thank Jim Ley andDoug Schepers for their assistance on the case study and Chapter 19 Special thanks to our lead editor,Sara Shlaer, for her gentle and not so gentle persuasive powers and attention to detail; to editor LisaThibault, for her thoughtful assistance; and to Phred Menyhert, for a rigorous technical edit Many thanks

to our acquisitions editor, Jim Minatel, who has shepherded this book through many incarnations

Where XML Can Be Used, and What You Can Use It For 20

Part II: Validation 93

Creating Elements with Simple Content and Attributes 185

Part III: Processing 247

Chapter 8: XSLT 287

Influencing the Output with the <xsl:output> Element 306

Named Templates and the <xsl:call-template> Element 322

Part IV: Databases 337

Exercise Questions 373

Two Ways to View DOM Nodes 448

Part VI: Communication 519

Exercise Questions 605

Part VII: Display 689

XForms Form Controls 817

Chapter 22: Case Study: Payment Calculator — Ruby on Rails Online

Appendix A: Exercise Solutions 873

Appendix E: XML Schema Element and Attribute Reference Online

Welcome to Beginning XML, Fourth Edition, the book I wish I’d had when I was first learning the language! When we wrote the first edition of this book, XML was a relatively new language but already gainingground fast and becoming more and more widely used in a vast range of applications By the time westarted the second edition, XML had already proven itself to be more than a passing fad, and was in factbeing used throughout the industry for an incredibly wide range of uses As we began the third edition,

it was clear that XML was a mature technology, but more important, it became evident that the XMLlandscape was dividing into several areas of expertise In this edition, we needed to categorize theincreasing number of specifications surrounding XML, which either use XML or provide functionality inaddition to the XML core specification

So what is XML? It’s a markup language, used to describe the structure of data in meaningful ways.Anywhere that data is input/output, stored, or transmitted from one place to another, is a potential fitfor XML’s capabilities Perhaps the most well-known applications are web-related (especially with thelatest developments in handheld web access—for which some of the technology is XML-based)

However, there are many other non-web-based applications for which XML is useful—for example, as areplacement for (or to complement) traditional databases, or for the transfer of financial informationbetween businesses News organizations, along with individuals, have also been using XML to dis-tribute syndicated news stories and blog entries

This book aims to teach you all you need to know about XML—what it is, how it works, what gies surround it, and how it can best be used in a variety of situations, from simple data transfer to usingXML in your web pages It answers the fundamental questions:

technolo-❑ What is XML?

❑ How do you use XML?

❑ How does it work?

❑ What can you use it for, anyway?

Who Is This Book For?

This book is for people who know that it would be a pretty good idea to learn XML but aren’t 100 cent sure why You’ve heard the hype but haven’t seen enough substance to figure out what XML is andwhat it can do You may be using development tools that try to hide the XML behind user interfaces andscripts, but you want to know what is really happening behind the scenes You may already be somehowinvolved in web development and probably even know the basics of HTML, although neither of thesequalifications is absolutely necessary for this book

per-What you don’t need is knowledge of markup languages in general This book assumes that you’re new

to the concept of markup languages, and we have structured it in a way that should make sense to thebeginner and yet quickly bring you to XML expert status

The word “Beginning” in the title refers to the style of the book, rather than the reader’s experiencelevel There are two types of beginner for whom this book is ideal:

❑ Programmers who are already familiar with some web programming or data exchange niques Programmers in this category will already understand some of the concepts discussedhere, but you will learn how you can incorporate XML technologies to enhance those solutionsyou currently develop

tech-❑ Those working in a programming environment but with no substantial knowledge or ence of web development or data exchange applications In addition to learning how XML tech-nologies can be applied to such applications, you will be introduced to some new concepts tohelp you understand how such systems work

experi-How This Book Is Organized

We’ve arranged the subjects covered in this book to take you from novice to expert in as logical a ner as we could In this Fourth Edition, we have structured the book in sections that are based on vari-ous areas of XML expertise Unless you are already using XML, you should start by reading the

man-introduction to XML in Part I From there, you can quickly jump into specific areas of expertise, or, if youprefer, you can read through the book in order Keep in mind that there is quite a lot of overlap in XML,and that some of the sections make use of techniques described elsewhere in the book

❑ We begin by explaining what exactly XML is and why the industry felt that a language like thiswas needed

❑ After covering the why, the next logical step is the how, so we show you how to create

well-formed XML

❑ Once you understand the whys and hows of XML, you’ll go on to some more advanced thingsyou can do when creating your XML documents, to make them not only well formed, but valid.(And you’ll learn what “valid” really means.)

❑ After you’re comfortable with XML and have seen it in action, we unleash the programmerwithin and look at an XML-based programming language that you can use to transform XMLdocuments from one format to another

❑ Eventually, you will need to store and retrieve XML information from databases At this point,you will learn not only the state of the art for XML and databases, but also how to query XMLinformation using an SQL-like syntax called XQuery

❑ XML wouldn’t really be useful unless you could write programs to read the data in XML ments and create new XML documents, so we’ll get back to programming and look at a couple

docu-of ways that you can do that

❑ Understanding how to program and use XML within your own business is one thing, but ing that information to a business partner or publishing it to the Internet is another You’ll learnabout technologies that use XML that enable you to send messages across the Internet, publishinformation, and discover services that provide information

send-❑ Since you have all of this data in XML format, it would be great if you could easily display it topeople, and it turns out you can We’ll show you an XML version of HTML called XHTML.You’ll also look at a technology you may already be using in conjunction with HTML docu-ments called CSS CSS enables you to add visual styles to your XML documents In addition,you’ll learn how to design stunning graphics and make interactive forms using XML.

❑ Finally, we end with a case study, which should help to give you ideas about how XML can beused in real-life situations, and which could be used in your own applications

What’s Covered in This Book

This book builds on the strengths of the earlier editions, and provides new material to reflect thechanges in the XML landscape—notably XQuery, RSS and Atom, and AJAX Updates have been made toreflect the most recent versions of specifications and best practices throughout the book In addition tothe many changes, each chapter has a set of exercise questions to test your understanding of the mate-rial Possible solutions to these questions appear in Appendix A

Here we cover some basic concepts, introducing the fact that XML is a markup language (a bit like

HTML) whereby you can define your own elements, tags, and attributes (known as a vocabulary) You’ll

see that tags have no presentation meaning—they’re just a way to describe the structure of the data

Part II: Validation

In addition to the well-formedness rules you learn in Part I, you will most likely want to learn how tocreate and use different XML vocabularies This Part introduces you to DTDs, XML Schemas, andRELAX NG: three languages that define custom XML vocabularies We also show you how to utilizethese definitions to validate your XML documents

Chapter 4: Document Type Definitions

You can specify how an XML document should be structured, and even provide default values, using

Document Type Definitions (DTDs) If XML conforms to the associated DTD, it is known as valid XML.

This chapter covers the basics of using DTDs

Chapter 5: XML Schemas

XML Schemas, like DTDs, enable you to define how a document should be structured In addition todefining document structure, they enable you to specify the individual datatypes of attribute values andelement content They are a more powerful alternative to DTDs

Chapter 6: RELAX NG

RELAX NG is a third technology used to define the structure of documents In addition to a new syntaxand new features, it takes the best from XML Schemas and DTDs, and is therefore very simple and verypowerful RELAX NG has two syntaxes; both the full syntax and compact syntax are discussed

Part III: Processing

In addition to defining and creating XML documents, you need to know how to work with documents

to extract information and convert it to other formats In fact, easily extracting information and ing it to other formats is what makes XML so powerful

Part IV: Databases

Creating and processing XML documents is good, but eventually you will want to store those ments This section describes strategies for storing and retrieving XML documents and document frag-ments from different databases

docu-Chapter 9: XQuery, the XML Query Language

Very often, you will need to retrieve information from within a database XQuery, which is built onXPath and XPath2, enables you to do this in an elegant way

Chapter 10: XML and Databases

XML is perfect for structuring data, and some traditional databases are beginning to offer support for XML This chapter discusses these, and provides a general overview of how XML can be used in

an n-tier architecture In addition, new databases based on XML are introduced

Part V: Programming

At some point in your XML career, you will need to work with an XML document from within a customapplication The two most popular methodologies, the Document Object Model (DOM) and the SimpleAPI for XML (SAX), are explained in this part

Chapter 11: The Document Object Model (DOM)

Programmers can use a variety of programming languages to manipulate XML using the DocumentObject Model’s objects, interfaces, methods, and properties, which are described in this chapter

Chapter 12: Simple API for XML (SAX)

An alternative to the DOM for programmatically manipulating XML data is to use the Simple API forXML (SAX) as an interface This chapter shows how to use SAX and utilizes examples from the Java SAXAPI

Part VI: Communication

Sending and receiving data from one computer to another is often difficult, but several technologies havebeen created to make communication with XML much easier In this part we discuss RSS and content syn-dication, as well as web services and SOAP This edition includes a new chapter on Ajax techniques

Chapter 13: RSS, Atom, and Content Syndication

RSS is an actively evolving technology that is used to publish syndicated news stories and website maries on the Internet This chapter not only discusses how to use the different versions of RSS andAtom, it also covers the future direction of the technology In addition, we demonstrate how to create asimple newsreader application that works with any of the currently published versions

sum-Chapter 14: Web Services

Web services enable you to perform cross-computer communications This chapter describes web vices and introduces you to using remote procedure calls in XML (using XML-RPC and REST), as well asgiving you a brief look at major topics such as SOAP Finally, it breaks down the assortment of specifica-tions designed to work in conjunction with web services

ser-Chapter 15: SOAP and WSDL

Fundamental to XML web services, the Simple Object Access Protocol (SOAP) is one of the most popularspecifications for allowing cross-computer communications Using SOAP, you can package up XML doc-uments and send them across the Internet to be processed This chapter explains SOAP and the WebServices Description Language (WSDL) that is used to publish your service

Chapter 16: Ajax

Ajax enables you to utilize JavaScript with web services and SOAP, or REST communications

Additionally, Ajax patterns can be used within web pages to communicate with the web server withoutrefreshing This chapter is new to the Fourth Edition

Part VII: Display

Several XML technologies are devoted to displaying the data stored inside of an XML document Some

of these technologies are web-based, and some are designed for applications and mobile devices In thispart we discuss the primary display strategies and formats used today

Chapter 17: Cascading Style Sheets (CSS)

Website designers have long been using Cascading Style Sheets (CSS) with their HTML to easily makechanges to a website’s presentation without having to touch the underlying HTML documents Thispower is also available for XML, enabling you to display XML documents right in the browser Or, if youneed a bit more flexibility with your presentation, you can use XSLT to transform your XML to HTML orXHTML and then use CSS to style these documents

Chapter 18: XHTML

XHTML is a new version of HTML that follows the rules of XML In this chapter we discuss the ences between HTML and XHTML, and show you how XHTML can help make your sites available to awider variety of browsers, from legacy browsers to the latest browsers on mobile phones

differ-Chapter 19: Scalable Vector Graphics (SVG)

Do you want to produce a custom graphic using XML? SVG enables you to describe a graphic usingXML-based vector commands In this chapter we teach you the basics of SVG and then dive into a morecomplex SVG-based application that can be published to the Internet

Chapter 20: XForms

XForms are XML-based forms that can be used to design desktop applications, paper-based forms, and

of course XHTML-based forms In this chapter we demonstrate both the basics and some of the moreinteresting uses of XForms

Part VIII: Case Study

Throughout the book you’ll gain an understanding of how XML is used in web, business-to-business (B2B),data storage, and many other applications The case study covers an example application and shows howthe theory can be put into practice in real-life situations The case study is new to this edition

Chapter 21: Case Study: Payment Calculator

This case study explores some of the possibilities and strategies for using XML in your website Itincludes an example that demonstrates a loan payment calculator by creating a web page using XHTMLand CSS, communicating with a local web service using AJAX, utilizing an XML Schema to build datastructures in NET, and ultimately using the Document Object Model to display the results in SVG Anonline version of this case study on the book’s website covers the same material using Ruby on Railsinstead of NET

Appendixes

Appendix A provides answers to the exercise questions that appear throughout the book The remainingappendixes provide reference material that you may find useful as you begin to apply the knowledgegained throughout the book in your own applications

The appendixes consist of the following:

❑ Appendix A: Exercise Solutions

❑ Appendix B: XPath Reference

❑ Appendix C: XSLT Reference

❑ Appendix D: The XML Document Object Model

❑ Appendix E: XML Schema Element and Attribute Reference

❑ Appendix F: XML Schema Datatypes Reference

❑ Appendix G: SAX 2.0.2 ReferenceAppendixes A, B, and C are included within the book; Appendixes D–G are available on the book’s website

What You Need to Use This Book

Because XML is a text-based technology, all you really need to create XML documents is Notepad or anequivalent text editor However, to truly appreciate some of these samples in action, you might want tohave a current Internet browser that can natively read XML documents, and even provide error mes-sages if something is wrong In any case, screenshots are provided throughout the book so that you cansee what things should look like Additionally, note the following:

❑ If you do have Internet Explorer, you also have an implementation of the DOM, which you mayfind useful in the chapters on that subject

❑ Some of the examples and the case studies require access to a web server, such as Microsoft’s IIS(or PWS) or Apache

❑ Throughout the book, other (freely available) XML tools are used, and we give instructions forobtaining these

Within the validation section of the book we provide instructions on how to use Codeplot (http://codeplot.com) Codeplot is an online collaborative code editor with support for a wide assortment ofXML technologies Because many validation tools require programming experience or large downloads,the examples in this section instead use Codeplot Codeplot can also be used to check the well-formed-ness of your XML documents, to transform XML documents using XSLT, and to assist you in codingXHTML, CSS, and SVG The editor is free and was built using many of the techniques described in thisbook

Additionally, we have attempted to show the use of XML in a variety of programming languages,including Java, JavaScript, PHP, Python, Visual Basic, ASP, C#, and Ruby on Rails Therefore, while there

is a good chance that you will see an example written in your favorite programming language, there isalso a good chance you will encounter an example in a language you have never used Whenever a newlanguage is introduced, we include information on downloading and installing the necessary tools touse it Because our focus is XML, regardless of which programming language is used in an example, thecore XML concept is explained in detail

Conventions

To help you get the most from the text and keep track of what’s happening, we’ve used several tions throughout the book

conven-Try It Out

The Try It Out is an exercise you should work through, following the text in the book

1. They usually consist of a set of steps

2. Each step has a number

3. Follow the steps with your copy of the database.

How It Works

After each Try It Out, the code is explained in detail

Tips, hints, tricks, and asides to the current discussion are offset and placed in italics like this.

As for styles in the text:

❑ We highlight new terms and important words when we introduce them.

❑ We show filenames, URLs, and code within the text like so: persistence.properties

❑ We present code in two different ways:

In code examples we highlight new and important code with a gray background

The gray highlighting is not used for code that’s less important in the presentcontext, or has been shown before

Boxes like this one hold important, not-to-be forgotten information that is directly

relevant to the surrounding text.

Source Code

As you work through the examples in this book, you may choose either to type in all the code manually

or to use the source code files that accompany the book All of the source code used in this book is able for download at www.wrox.com Once at the site, simply locate the book’s title (either by using theSearch box or by using one of the title lists) and click the Download Code link on the book’s detail page

avail-to obtain all the source code for the book

Because many books have similar titles, you may find it easiest to search by ISBN; this book’s ISBN is

SB 978-0-470-11487-2

Once you download the code, just decompress it with your favorite compression tool Alternately, youcan go to the main Wrox code download page at www.wrox.com/dynamic/books/download.aspxtosee the code available for this book and all other Wrox books

Errata

We make every effort to ensure that there are no errors in the text or in the code However, no one is fect, and mistakes do occur If you find an error in one of our books, such as a spelling mistake or afaulty piece of code, we would be very grateful for your feedback By sending in errata you may saveanother reader hours of frustration, and at the same time you will be helping us provide even higherquality information

per-To find the errata page for this book, go to www.wrox.comand locate the title using the Search box orone of the title lists Then, on the book details page, click the Book Errata link On this page you can viewall errata that has been submitted for this book and posted by Wrox editors A complete book list, includ-ing links to each book’s errata, is also available at www.wrox.com/misc-pages/booklist.shtml

If you don’t spot “your” error on the Book Errata page, go to www.wrox.com/contact/

techsupport.shtmland complete the form there to send us the error you have found We’ll check the information and, if appropriate, post a message to the book’s errata page and fix the problem in subsequent editions of the book

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sys-At http://p2p.wrox.comyou will find a number of different forums that will help you not only as youread this book, but also as you develop your own applications To join the forums, just follow these steps:

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ques-Part I Introduction

Chapter 1: What Is XML?

Chapter 2: Well-Formed XML

Chapter 3: XML Namespaces