Wrox Beginning XML 2nd Edition Dec 2001 ISBN 0764543946 pdf

  

  Beginning XML, 2nd Edition: XML Schemas, SOAP,

  XSLT, DOM, and SAX 2.0 by David Hunter, Kurt

  ISBN:0764543946 Cagle, Chris Dix et al. Wrox Press © 2003 (784 pages) This book teaches you all you need to know about

  XML--what it is, how it works, what technologies surround it, and how it can best be used in a variety of situations, from simple data transfer to using XML in your web pages.

  Table of Contents

  

• What is XML?

  

  

• Well-Formed XML

  

  

• XML Namespaces

  

  

• XSLT

  

  

• Document Type Definitions

  

  

• XML Schemas

  

  

• Advanced XML Schemas

  

  

  

• The Document Object Model (DOM)

  

  

• The Simple API for XML (SAX)

  

   Ch apt

• SOAP

  er

  10

• Displaying XML

  

  

• XML and Databases

  

  

• Linking and Querying XML

  

  

  

   - XPath Reference

   - Schema Element and Attribute Reference

• Schema Datatypes Reference

  

• SAX 2.0: The Simple API for XML

  

  

  

  Back Cover Extensible Markup Language (XML) is a rapidly maturing technology with powerful real-world applications, particularly for the management, display, and transport of data. Together with its many related technologies, it has become the standard for data and document delivery on the Web. This book teaches you all you need to know about XML—what it is, how it works, what technologies surround it, and how it can best be used in a variety of situations, from simple data transfer to using XML in your web pages. It builds on the strengths of the first edition, and provides new material to reflect the changes in the XML landscape—notably SOAP and Web Services, and the publication of the XML Schemas Recommendation by the W3C. Who is this book for?

   Beginning XML, 2nd Edition is for any developer who is interested in learning to use XML in web, e-commerce,

  or data storage applications. Some knowledge of mark up, scripting, and/or object oriented programming languages is advantageous, but no essential, as the basis of these techniques is explained as required. What does this book cover?

   XML syntax and writing well-formed XML  Using XML Namespaces  Transforming XML into other formats with XSLT  XPath and XPointer for locating specific XML data  XML validation using DTDs and XML Schemas  Manipulating XML documents with the DOM and SAX 2.0  SOAP and Web Services  Displaying XML using CSS and XSL  Incorporating XML into traditional databases and n-tier architectures  XLink for linking XML and non-XML resources.

  

  

Beginning XML, 2nd Edition-XML Schemas, SOAP,XSLT,DOM, and SAX 2.0 Kurt Cagle Chris Dix David Hunter Roger Kovack Jon Pinnock Jeff Rafter

  Published by Wiley Publishing, Inc. 10475 Crosspoint Boulevard Indianapolis, IN 46256

  

  Copyright © 2003 by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada Library of Congress Card Number: 2003107073

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   Trademark Acknowledgements

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   Credits Authors

  Kurt Cagle Chris Dix David Hunter Roger Kovack Jonathon Pinnock Jeff Rafter

   Technical Reviewers

  Steve Baker David Beauchemin Martin Beaulieu Natalia Bortniker Oli Gauti Gudmundsson Paul Houle Graham Innocent Sachin Kanna Sing Li Steven Livingstone Nikola Ozu Jeff Rafter Gareth Reakes Eddie Robertsson David Schultz Ian Stokes-Rees

   Category Managers

  Simon Cox Dave Galloway

  Technical Architect

   Technical Editors

  Sarah Larder Simon Mackie

   Indexers'

  Michael Brinkman Fiona Murray

   Production Manager

  Liz Toy

   Production Project Co-ordinator

  Mark Burdett

   Author Agent

  Marsha Collins

   Production Assistant

  Abbie Forletta

   Project Manager

  Vicky Idiens

   Cover

  Dawn Chellingworth

   Proof Reader

  Keith Westmoreland

   About the Authors Kurt Cagle

  Kurt Cagle is a writer and developer specializing in XML and Internet related issues. He has written eight books and more than one hundred articles on topics ranging from Visual Basic programming to the impact of the Internet on society, and has consulted for such companies as Microsoft, Nordstrom, AT&T and others. He also helped launch Fawcette's XML Magazine and has been the DevX DHTML and XML Pro for nearly two years.

  one of the authors of Professional XML Web Services, and he frequently writes and speaks on the topic of XML and Web Services. Chris is Lead Developer for NavTraK, Inc., a leader in automatic vehicle location systems located in Salisbury, Maryland, where he develops Web Services and system architecture. He can be reached at .

  

I would like to thank my wife Jennifer and my wonderful sons Alexander and Calvin for their love and

support. I would also like to thank the people at Wrox for this opportunity, and for their technical expertise in helping make this possible.

   Chris Dix contributed Case Study 2 to this book.

   David Hunter

  David Hunter is a Senior Architect for MobileQ, a leading mobile software solutions developer, and the first company to ship an XML-based mobility server. David has extensive experience building scalable applications, and provides training on XML. He also works closely with the team that develops MobileQ's flagship product, XMLEdge, which delivers the ideal mobile user experience on a diverse number of mobile devices.

   First of all, I would like to thank God for the incredible opportunities he has given me to do something I love, and even write books about it. I pray that the glory will go to him. I would also like to thank Wrox's editors; if this book is helpful, easy to read, and easy to understand, it's because the editors made it that way. And finally, I'd like to thank the person who gave me the most support, but probably doesn't even realize it. Thank you, Andrea, for helping me through this."

  

  

  

  

  

  10

  

   David Hunter contributed , , , , , , , and to this book.

   Roger Kovack

  Roger Kovack has more than 25 years of software development experience, started by programming medical research applications in Fortran on DEC machines at the University of California. More recently he has consulted to Wells Fargo and Bank of America, developing departmental information systems on desktop and client/server platforms. Bitten by Java and the web bug in the mid '90s he developed web applications for Commerce One, a major B2B software vendor; and for LookSmart.com, one of the best known and still operating web portals. He was instrumental in bringing Java into those organizations to replace ASP and C++. Roger can be contacted on

  

  

"My deep thanks to my wife, Julie, for the encouragement and support for writing this chapter. I'm also

endlessly grateful for the help and attention the editorial team at Wrox Press provided. Their concern for

quality content can't be overstated. Words can't express my sorrow and compassion for the innocent victims and their families whose lives were

shattered by the terrorist attacks on New York and Washington DC on September 11, 2001. The personal,

permanent wound that has caused makes me plead for world peace." Roger Kovack contributed Case Study 1 to this book.

   Jon Pinnock

  Jonathan Pinnock started programming in Pal III assembler on his school's PDP 8/e, with a massive 4K of memory, back in the days before Moore's Law reached the statute books. These days he spends most of his time developing and extending the increasingly successful PlatformOne product set that his company, JPA, markets to the financial services community. JPA's home page is at:

   "My heartfelt thanks go to Gail, who first suggested getting into writing, and now suffers the consequences on a fairly regular basis, and to Mark and Rachel, who just suffer the consequences."

  past two years, he has worked with Standfacts Credit Services, a Los Angeles based company, developing XML interfaces for use in the mortgage industry. He also leads the XML development for Defined Systems, a web hosting company founded with his long time friend Dan English. In his free time, Jeff composes sonnets, plays chess in parks,

   "I thank God for his love and grace in all things. I would also like to thank my beautiful wife Ali, who is the embodiment of that love in countless ways. She graciously encouraged me to pursue my dreams at any cost.

Thanks also to Mike McKay who was first a servant and then a friend as I worked through the writing

process.

   Finally, I would like to thank Vicky, Peter, Sarah, Simon, Victoria, Marsha and everyone at Wrox for the opportunity and support. I would also like to express my gratitude to the invaluable reviewers." Jeff Rafter contributed ,

  

  

Introduction

  Welcome to Beginning XML, 2nd Edition, the book I wish I'd had when I was first learning the language! When we wrote the 1st Edition of this book, XML was a relatively new language, but was already gaining ground fast, and becoming more and more widely used in a vast range of applications. By the time we started the 2nd Edition,

  XML had already proven itself to be more than a passing fad, and was in fact being used throughout the industry for an incredibly wide range of uses. There are also quite a number of specifications surrounding XML, which either use

  XML or provide functionality in addition to the XML core specification, which aim to allow developers to do some pretty powerful things. 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 fit for XML's capabilities. Perhaps the most well known applications are web related (especially with the latest developments in handheld web access?for which some of the technology is XML-based). But there are many other non-web based applications where XML is useful?for example as a replacement for (or to complement) traditional databases, or for the transfer of financial information between businesses. This book aims to teach you all you need to know about XML?what it is, how it works, what technologies surround it, and how it can best be used in a variety of situations, from simple data transfer to using XML in your web pages. It will answer the fundamental questions:

   What is XML?

   How do I use XML?

   How does it work?

   What can I 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 the language, but aren't 100% sure why. You've heard the hype, but haven't seen enough substance to figure out what XML is, and what it can do. You may already be somehow involved in web development, and probably even know the basics of HTML, although neither of these qualifications is absolutely necessary for this book.

  What you don't need is knowledge of SGML (XML's predecessor), or even markup languages in general. This book assumes that you're new to the concept of markup languages, and we have tried to structure it in a way that will make sense to the beginner, 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 experience level. There are two types of beginner for whom this book will be ideal:

  

  Programmers who are already familiar with some web programming or data exchange techniques. You will already be used to some of the concepts discussed here, but will learn how you can incorporate XML technologies to enhance those solutions you currently develop.

   Those working in a programming environment but with no substantial knowledge or experience of web development or data exchange applications. As well as learning how XML technologies can be applied to such applications, you will be introduced to some new concepts to help you understand how such systems work.

  

  

What's Covered in this Book?

  I've tried to arrange the subjects covered in this book to take you from no knowledge to expert, in as logical a manner as I could. We'll be using the following format:

   First, we'll be looking at what exactly XML is, and why the industry felt that a language like this was needed.

   After covering the why, the next logical step is the how, so we'll be seeing how to create well-formed XML.

   Once we understand the whys and hows of XML, we'll unleash the programmer within, and look at an

  XML-based programming language that we can use to transform XML documents from one format to another.

   Now that you're comfortable with XML, and have seen it in action, we'll go on to some more advanced things you can do when creating your XML documents, to make them not only well-formed, but valid. (And we'll talk about what "valid" really means).

   XML wouldn't really be useful unless we could write programs to read the data in XML documents, and create new XML documents, so we'll get back to programming, and look at a couple of ways that we can do that. We'll also take a look at a technology that allows us to send messages across the Internet, which uses XML.

   Since we have all of this data in XML format, it would be great if we could easily display it to people, and it turns out we can. We'll look at a technology you may already have been using in conjunction with HTML documents that also works great with XML. We'll also look at how this data fits in with traditional databases, and even how we can link XML documents to one another.

   And finally, we'll finish off with some case studies, which should help to give you ideas on how XML can be used in real life situation, and which could be used in your own applications.

  This book builds on the strengths of the first edition, and provides new material to reflect the changes in the XML landscape-notably SOAP and Web Services, and the publication of the XML Schemas Recommendation by the W3C-since we first published it in June 2000. The chapters are broken down as follows:

  you can define your own elements, tags and attributes (known as a vocabulary). We'll see that tags have no presentation meaning-they're just a way of describing the structure of data.

  : Well-Formed XML

  As well as explaining what well-formed XML is, we'll take a look at the rules that exist (the XML 1.0 Recommendation) for naming and structuring elements-you need to comply with these rules if your XML is to be well-formed.

   : XSLT XML can be transformed into other XML, HTML, and other formats using XSLT stylesheets, which are introduced

  here. The XPath language, used to locate sections in the XML document, is also covered. This chapter has been completely overhauled from the first edition.

   : Document Type Definitions We can specify how an XML document should be structured, and even give 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. Though we have shifted our emphasis on validation technologies in this edition (by giving more coverage to XML Schemas), we still recognise the importance of DTDs in XML programming, and have provided a completely new and refocused chapter on the subject.

   : The Simple API for XML (SAX) An alternative to the DOM for programmatically manipulating XML data is to use the Simple API for XML (SAX)

  as an interface. This chapter shows how to use SAX, and has been updated from the first edition to focus on SAX 2.0.

  Chapter 10 : SOAP The Simple Object Access Protocol (SOAP) is a specification for allowing cross-computer communications, and is

  fundamental to XML Web Services. We can package up XML documents, and send them across the Internet to be processed. This chapter explains SOAP and XML Web Services, and is new to this edition.

  : Displaying XML

  Web site designers have long been using Cascading Style Sheets (CSS) with their HTML to easily make changes to a web site's presentation without having to touch the underlying HTML documents. This power is also available for

  XML, allowing you to display XML documents right in the browser. Or, if you need a bit more flexibility with your presentation, you can use XSLT to transform your XML to HTML or XHTML.

   : XML and Databases XML is perfect for structuring data, and some traditional databases are beginning to offer support for XML. These are discussed, as well as a more general overview of how XML can be used in an n-tier architecture.

  : Linking XML

   We can locate specific parts of the XML document using XPath and XPointer. We can also link sections of documents and other resources using XLink. Both XPointer and XLink are described in this chapter. Case Studies 1 and 2 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. These case studies cover some example applications and show how the theory can be put into practice in real life situations. Both are new to this edition.

Appendices

  These provide reference material that you may find useful as you begin to apply the knowledge gained throughout the book in your own applications.

  

  

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 your equivalent text editor. However, to really see some of these samples in action, you might want to have Internet Explorer 5 or later, since this browser can natively read XML documents, and even provide error messages if something is wrong. For readers without IE, there will be some screenshots throughout the book, so that you can see what things would look like. If you do have IE, you also have an implementation of the DOM, which you may find useful in the chapter on that subject.

  Some of the examples, and the case studies, require access to a web server, such as Microsoft's IIS (or PWS). Throughout the book, other (freely available) XML tools will be used, and we'll give instructions for obtaining these at the appropriate place.

  

  

Conventions

  To help you understand what's going on, and in order to maintain consistency, we've used a number of conventions throughout the book: When we introduce new terms, we highlight them.

  Important These boxes hold important information.

   Advice, hints, and background information comes in an indented, italicized font like this.

Try It Out

  After learning something new, we'll have a Try It Out section, which will demonstrate the concepts learned, and get you working with the technology.

How It Works

  After a Try It Out section, there will sometimes be a further explanation, to help you relate what you've done to what you've just learned. Words that appear on the screen in menus like the File or Window menu are in a similar font to what you see on screen. URLs are also displayed in this font. On the occasions when we'll be running the examples from the command line, we'll show the command and the results like this:

  >msxsl blah.xml blah.xsl

  root

  < > < results/ >

  /root

  < > Keys that you press on the keyboard, like Ctrl and Enter, are in italics.

  We use two font styles for code. If it's a word that we're talking about in the text, for example, when discussing functionNames(), , it will be in a fixed pitch font. If it's a block of code that you can type in and run, or part of such a block, then it's also in a gray box:

  <html> <head> <title>Simple Example</title> </head> <body> <p>Very simple HTML.</p> </body> </html>

  Sometimes you'll see code in a mixture of styles, like this:

  <html> <head> <title>Simple Example</title>

  <body> <p>Very simple HTML.</p> </body> </html>

  In this case, we want you to consider the code with the gray background, for example to modify it. The code with a white background is code we've already looked at, and that we don't wish to examine further.

  

  

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  Chapter 1: What is XML? Overview

Extensible Markup Language (XML) is a buzzword you will see everywhere on the Internet, but it's also a

rapidly maturing technology with powerful real-world applications, particularly for the management, display and organization of data. Together with its many related technologies, which will be covered in later chapters, it is an essential technology for anyone using markup languages on the Web or internally. This chapter will introduce you to some of the basics of XML, and begin to show you why it is so important to learn about it. We will cover:

   The two major categories of computer file types?binary files and text files?and the advantages and disadvantages of each

   The history behind XML, including other markup languages?SGML and HTML

   How XML documents are structured as hierarchies of information

   A brief introduction to some of the other technologies surrounding XML, which you will be working with throughout the book

   A quick look at some areas where XML is proving to be useful

   While there are some short examples of XML in this chapter, you aren't expected to understand what's going on just yet. The idea is simply to introduce the important concepts behind the language, so that throughout the book you can see not only how to use XML, but also why it works the way that it does.

  

  

Of Data, Files, and Text

  XML is a technology concerned with the description and structuring of data, so before we can really delve into the concepts behind XML, we need to understand how data is stored and accessed by computers. For our purposes, there are two kinds of data files that are understood by computers: text files and binary files.

Binary Files

  A binary file, at its simplest, is just a stream of bits (1's and 0's). It's up to the application that created a binary file to understand what all of the bits mean. That's why binary files can only be read and produced by certain computer programs, which have been specifically written to understand them. For example, when a document is created with a word processor, the program creates a binary file in its own proprietary format. The programmers who wrote the word processor decided to insert certain binary codes into the document to denote bold text, other codes to denote page breaks, and many other codes for all of the information that needs to go into these documents. When you open a document in the word processor it interprets those codes, and displays the properly formatted text on the screen, or prints it to the printer. The codes inserted into the document are meta data, or information about information. Examples could be "this word should be in bold", "that sentence should be centered", etc. This meta data is really what differentiates one file type from another; the different types of files use different kinds of meta data. For example, a word processing document will have different meta data from a spreadsheet document, since they are describing different things. Not so obviously, word processing documents from different word processing applications will also have different metadata because the applications were written differently: As the above diagram shows, a document created with one word processor cannot be assumed to be readable in or used by another, because the companies who write word processors all have their own proprietary formats for their data files. So Word documents open in Microsoft Word, and WordPerfect documents open in WordPerfect. Luckily for us most word processors come with translators, which can translate documents from other word processors into formats that can be understood natively. Of course, many of us have seen the garbage that sometimes occurs as a result of this translation; sometimes applications are not as good as we'd like them to be at converting the information.

  The advantage of binary file formats is that it is easy for computers to understand these binary codes, meaning that they can be processed much faster, and they are very efficient for storing this meta data. There is also a disadvantage, as we've seen, in that binary files are "proprietary". You might not be able to open binary files created by one application in another application, or even in the same application running on another platform.

   Text Files

  Like binary files, text files are also streams of bits. However, in a text file these bits are grouped together in standardized ways, so that they always form numbers. These numbers are then further mapped to characters. For example, a text file might contain the bits:

  1100001 This group of bits could be translated as the number "97", which would then be further translated into the letter "a".

   This example makes a number of assumptions. A better description of how numbers are represented in text files is given in the section on "Encoding" in

  simple text editor. If I create a text document, anyone in the world can read it (as long as they understand English, of course), in any text editor they wish. There are still some issues, like the fact that different operating systems treat line ending characters differently, but it is much easier to share information with others than with binary formats. The following diagram shows just some of the applications on my machine that are capable of opening text files. Some of these programs will just allow me to view the text, while others will let me edit it as well.

  In its beginning, the Internet was almost completely text-based, which allowed people to communicate with relative ease. This contributed to the explosive rate at which the Internet was adopted, and to the ubiquity of applications like e-mail, the World Wide Web, newsgroups, etc. The disadvantage of text files is that it's more difficult and bulky to add other information?our meta data in other words. For example, most word processors allow you to save documents in text form, but if you do then you can't mark a section of text as bold, or insert a binary picture file. You will simply get the words, with none of the formatting.

A Brief History of Markup

  We can see that there are advantages to binary file formats (easy to understand by a computer, compact), as well as advantages to text files (universally interchangeable). Wouldn't it be ideal if there were a format that combined the universality of text files with the efficiency and rich information storage capabilities of binary files? This idea of a universal data format is not new. In fact, for as long as computers have been around, programmers have been trying to find ways to exchange information between different computer programs. An early attempt to combine a universally interchangeable data format with rich information storage capabilities was SGML (Standard

  

Generalized Markup Language). This is a text-based language that can be used to mark up data?that is, add

meta data?in a way which is self-describing. We'll see in a moment what self-describing means.

  SGML was designed to be a standard way of marking up data for any purpose, and took off mostly in large document management systems. It turns out that when it comes to huge amounts of complex data there are a lot of considerations to take into account and, as a result, SGML is a very complicated language. With that complexity comes power though.

  A very well-known language, based on the SGML work, is the HyperText Markup Language, or HTML. HTML uses many of SGML's concepts to provide a universal markup language for the display of information, and the linking of different pieces of information. The idea was that any HTML document (or web page) would be presentable in any application that was capable of understanding HTML (termed a web browser).

  Not only would that browser be able to display the document, but also if the page contained links (termed hyperlinks) to other documents, the browser would be able to seamlessly retrieve them as well. Furthermore, because HTML is text-based, anyone can create an HTML page using a simple text editor, or any number of web page editors, some of which are shown below: Even many word processors, such as WordPerfect and Word, allow you to save documents as HTML. Think about the ramifications of these two diagrams: any HTML editor, including a simple text editor, can create an HTML file, and that HTML file can then be viewed in any web browser on the Internet!

  

  

So What is XML?

  Unfortunately, SGML is such a complicated language that it's not well suited for data interchange over the web. And, although HTML has been incredibly successful, it's also limited in its scope: it is only intended for displaying documents in a browser. The tags it makes available do not provide any information about the content they encompass, only instructions on how to display that content. This means that I could create an HTML document which displays information about a person, but that's about all I could do with the document. I couldn't write a program to figure out from that document which piece of information relates to the person's first name, for example, because HTML doesn't have any facilities to describe this kind of specialized information. In fact, that program wouldn't even know that the document was about a person at all.

  Extensible Markup Language (XML) was created to address these issues.

   Note that it's spelled "Extensible", not "eXtensible". Mixing these up is a common mistake.

  XML is a subset of SGML, with the same goals (mark up of any type of data), but with as much of the complexity eliminated as possible. XML was designed to be fully compatible with SGML, which means that any document which follows XML's syntax rules is by definition also following SGML's syntax rules, and can therefore be read by existing SGML tools. It doesn't go both ways though, so an SGML document is not necessarily an XML document.

  It is important to realize, however, that XML is not really a "language" at all, but a standard for creating languages that meet the XML criteria (we'll go into these rules for creating XML documents in

  and I want to be able to share that information with others and I also want to be able to use that information in a computer program. Instead of just creating a text file like this:

  John Doe

  or an HTML file like this:

  <html> <head><title>Name</title></head> <body> <p>John Doe</p> </body> </html>

  I might create an XML file like this: