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Anonymous
Posted Sun Nov 10 00:00:00 EST 2002
If you are already using XML, it is probably with DTDs, as this was the first implementation of XML. Both came out of SGML, in which the role of DTDs was defined in the early 1990s. Unfortunately, the drawbacks of DTDs were not fully appreciated until they began to be widely used in XML. A DTD cannot easily constrain an integer variable to a range of values from 5 to 10, say. It has no conception of common primitive types like float or double found in many programming languages. Also, the structure of a DTD is quite unlike that of the XML document it supports. From the point of view of writing parsers, you end up effectively needing two parsing algorithms to read a DTD and an XML document. XML Schemas answer all these issues. Plus namespaces are built into them, to handle collisions in tag names when you use multiple Schemas in a document. With DTDs, namespaces came into being after DTDs were first defined, and had to be bolted on in a most awkward fashion. XML Schema notation for namespaces is much more natural. The problem right now with XML Schema is that it is new. Most XML books use DTDs, in part because when they were written, the Schema specification was not finished by W3C (in May 2001). Some XML books since then do describe Schema. They usually give a good overview and provide examples that work for the XML document examples they describe. So if you have an application that you want to write a Schema for, you can get started. But chances are, you soon run into problems if your application is not a carbon copy of a text's example. You soon need some Schema component or attribute whose usage or even existence was not disclosed in that book. This book addresses that shortfall. It provides at least one example of how to use every attribute of EVERY Schema element. A formidably comprehensive task. Which accounts for the near thousand page size. But this is far more than just some dictionary-style exposition. They describe important closely related issues, like how to use the DOM and Xerces SAX parsers, and the different outlooks these take. Also, from your viewpoint of how to write a Schema for YOUR application, they offer a top-down approach. Schemas can be result-oriented or data-oriented. You get enough details to help decide which case yours fits. This can greatly aid developing a facile "natural" Schema. One where once you have it and an example XML document that uses it, the layout taxonomy seems axiomatic. Which should be your goal. It is not enough to define a Schema that can hold all the information you have. The skill is in making a Schema that does that and has a clear, obvious logic. Because in many cases others, probably not as technically adept as you, get to fill in documents based on it. So the logic should be clear to them. Even if they do not directly write into an XML document, but build it from a GUI, the clearer the Schema, the easier it is for someone to build a GUI to populate a document based on it. The authors also provide a website (XMLSchemaReference.com) that has the code described in the book, and many more examples. Worth bookmarking. So try this book and its website if you need an authoritative guide to writing Schemas.
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The authoring and editorial teams for this book have worked hard to bring you the cleanest, clearest, and most complete XML schema reference source on the market. Endless sweat, research hours, code testing, tech and definition reviews and counter explanations, e-mail queries, dialogue, and debates passed before this book came to fruition. Earnest efforts, stress-filled moments, and writing deadlines have finally gotten us to press time. Here is what this book means to us.
The History
There are always new and hot technologies to write about (C++, Java, SQL, .NET, XML schema, and much more). There are qualified writers eager to write a clear and concise bestseller for your bookshelf. There are millions of software developers eager to learn. There are more than a few publishers to choose from. Ultimately there are several technical books on the market within months of any new product, platform, service, tool, or language's release that seeks to describe, explain, clarify, and elaborate on a given technology's importance, utility, and implementation. However, there are very few really good books on the "why and when" that will actually teach developers emerging technologies. In fact, the hardest types of books to write discuss emerging technologies, because there really aren't many good examples. Furthermore, even the "experts" frequently disagree on what is "right."
We spent many months--full time--writing this book. Collectively, we have something like 80 years of experience. Some of us are on the W3C Schema Working Group. We believe that this combined experience, as well as the determination writing this book, results in one of the few "really goodbooks" previously mentioned. It takes the right combination of technology, authors, publishers, and readers to pull off a book.
The Book
There are several, and probably soon to be lots, of books on the market that pertain to XML schemas. Despite this influx, we strongly believe that this book provides details few, if any, other books provide. Specifically, the overarching goal driving this book is to provide detailed examples of every XML schema component. In order to detail each component, this book contains an example of the corresponding schema document element, and all of the associated attributes. Many of the books on the market today provide surface details about schema components. However, this book provides detailed scenarios. Not only are there many pages and examples of each schema element, there is at least one example of every single attribute of every single XML schema document element. Having accomplished that colossal task, we added example after example integrating with many languages and technologies on many platforms. After all, what good is an XML schema by itself?
The Web Site
The sole purpose of this Web site is to provide an online reference for developers writing XML schemas. Nominally, the Web site provides a place to download all of the files created while writing this book. These files include not only the XML schemas and the source code in various languages, but also all of the test cases for even the one-line code snippets: all of the code in this book is tested!
The Web site is much more extensive than just a collection of files, however. In addition to the traditionally available downloads, XMLSchemaReference has lots simple online examples of every schema document element. There are tables for each element that indicate what attributes are possible, as well as a brief description. Although this Web site is not a tutorial, it is a fantastic quick reference for those who already understand schemas in general, but might forget the specific syntax. It is our hope that the Web site, like the book, becomes real reference material for lots of developers.
The Value
Our goal is to make it easy to create an XML schema--whether you need a tutorial to write your first schema document, or you just need a reference book to write your 5,000th. Having created a schema, this book also gives you the same levels of assistance to incorporate an XML schema into your application. This book provides as much support as you need, without ever getting in the way. Have fun working with XML schemas--we do!
We invite you now to take a tour through the world of XML schema components, beginning with the introduction provided for you in Chapter 1. We welcome your stories, additions, code samples, questions, feedback, and insights.
Table of Contents
Preface
The History
There are always new and hot technologies to write about (C++, Java, SQL, .NET, XML schema, and much more). There are qualified writers eager to write a clear and concise bestseller for your bookshelf. There are millions of software developers eager to learn. There are more than a few publishers to choose from. Ultimately there are several technical books on the market within months of any new product, platform, service, tool, or language's release that seeks to describe, explain, clarify, and elaborate on a given technology's importance, utility, and implementation. However, there are very few really good books on the "why and when" that will actually teach developers emerging technologies. In fact, the hardest types of books to write discuss emerging technologies, because there really aren't many good examples. Furthermore, even the "experts" frequently disagree on what is "right."
We spent many months—full time—writing this book. Collectively, we have something like 80 years of experience. Some of us are on the W3C Schema Working Group. We believe that this combined experience, as well as the determination writing this book, results in one of the few "really good books"previously mentioned. It takes the right combination of technology, authors, publishers, and readers to pull off a book.
The Book
There are several, and probably soon to be lots, of books on the market that pertain to XML schemas. Despite this influx, we strongly believe that this book provides details few, if any, other books provide. Specifically, the overarching goal driving this book is to provide detailed examples of every XML schema component. In order to detail each component, this book contains an example of the corresponding schema document element, and all of the associated attributes. Many of the books on the market today provide surface details about schema components. However, this book provides detailed scenarios. Not only are there many pages and examples of each schema element, there is at least one example of every single attribute of every single XML schema document element. Having accomplished that colossal task, we added example after example integrating with many languages and technologies on many platforms. After all, what good is an XML schema by itself?
The Web Site
The http://www.XMLSchemaReference.com Web site corresponds directly to this book. The sole purpose of this Web site is to provide an online reference for developers writing XML schemas. Nominally, the Web site provides a place to download all of the files created while writing this book. These files include not only the XML schemas and the source code in various languages, but also all of the test cases for even the one-line code snippets: all of the code in this book is tested!
The Web site is much more extensive than just a collection of files, however. In addition to the traditionally available downloads, http://www.XMLSchemaReference.com has lots simple online examples of every schema document element. There are tables for each element that indicate what attributes are possible, as well as a brief description. Although this Web site is not a tutorial, it is a fantastic quick reference for those who already understand schemas in general, but might forget the specific syntax. It is our hope that the Web site, like the book, becomes real reference material for lots of developers.
The Value
Our goal is to make it easy to create an XML schema—whether you need a tutorial to write your first schema document, or you just need a reference book to write your 5,000th. Having created a schema, this book also gives you the same levels of assistance to incorporate an XML schema into your application. This book provides as much support as you need, without ever getting in the way. Have fun working with XML schemas—we do!
We invite you now to take a tour through the world of XML schema components, beginning with the introduction provided for you in Chapter 1. We welcome your stories, additions, code samples, questions, feedback, and insights.
Cliff Binstockbinstock@pacifier.net
Dave Peterson
davep@acm.org
Mitch Smith
mitchsmith50@hotmail.com
Mike Wooding
woodinmi@mindspring.com
Chris Dix
cdix@soapworkshop.com
Chris Galtenberg
c@galtenberg.net