Press Release
July 19, 2002
Decoding W3C's Object-Oriented Specification: O'Reilly Releases "XML Schema"
Sebastopol, CA--Many developers see W3C XML Schema as the principal
language for defining the content and structure of XML documents, while
others resist the specification as unnecessarily complex, preferring to
use tools such as DTDs, Schematron or RELAX NG. Eric van der Vlist, the
author of the newly released XML Schema: The W3C's Object-Oriented Descriptions for XML
(O'Reilly, US $39.95), approaches this
controversy with a sober and objective view: W3C XML Schema, he says,
is both essential and potentially dangerous for XML.
"XML Schema is the most complex specification ever published by the
W3C," van der Vlist says. "The technology itself is complex, and the
specification was written in a way that's very difficult to read. Many
experts lack the objectivity necessary to show the limitations and
pitfalls of the technology. My book is an honest attempt to provide a
description of W3C XML Schema that is neither bashing nor praising."
Involved in developing ISO standards as the editor of the Document
Schema Definition Languages Part 5 specification describing "Object
Oriented XML Schema languages," van der Vlist is an XML consultant and
developer, creator and chief editor of XMLfr.org, and regular
contributor to XML.com and xmlhack.com. He wrote "XML Schema" for
O'Reilly because W3C XML Schema has become a key component of web
services specifications such as SOAP and WSDL, and most developers who
interchange XML documents will need to work with the specification on
some level.
Primarily designed as a tutorial--with design choices, best practices,
and limitations--"XML Schema" also serves as a reference to many
aspects of XML Schema creation and processing. Schemas, the book
explains, effectively serve as design tools for an array of XML-based
applications that enable developers to automate tasks such as
validation, code generation, documentation, data binding and query
optimization. Validation is the most common use for schemas, ensuring
that XML documents conform to expectations, simplifying the code needed
to process them.
W3C XML Schema's object-oriented approach enables XML developers to
create very precise document descriptions, using a method of
classification to derive types from other types. "Classification and
object-orientation are useful ways to leverage what we know at a
general level to a more specific level," van der Vlist explains. "For
example, if I know that a cheetah is a mammal, I can infer further
information about a cheetah--that it's warm-blooded and that female
cheetahs nurse their young--which I don't need to formalize
specifically for the cheetah. A similar principle applies to object
orientation programming and XML. Knowing that an element or an
attribute has a certain type may give me information, which allows me
to use algorithmic processes that apply to this type."
That, he asserts, is the big promise of both object orientation and W3C
XML Schema. Instead of writing documentation and processes for each
element and attribute--that is, for each object--developers can write
documentation and processes for each type, or class of objects, where
each type is used to describe several elements and attributes. The
danger lies in W3C XML Schema's uniqueness. Since trying to impose a
single schema language is as unrealistic as trying to impose a single
programming language, developers might actually create two distinct and
potentially incompatible types of XML applications: those that identify
elements and attributes by their datatypes (with W3C XML Schema), and
those that identify them by a set of rules or patterns (with other
schemas).
"Like it or not, most of us will have to use W3C XML Schema, and it's
up to us to use it for the better and not for the worse," van der Vlist
counsels. "My approach to writing the book was to make a critical
analysis of the features of the language, not taking anything for
granted. I'm convinced that this is the only useful and practical way
to approach this highly intrusive specification, and the purpose of my
book is to guide the reader as safely as possible through this tour."
Additional Resources:
XML Schema
By Eric van der Vlist
ISBN 0-596-00252-1, 400 pages, $39.95 US $61.95 CA
order@oreilly.com
1-800-998-9938; 1-707-827-7000
About O'Reilly
O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An active participant in the technology community, the company has a long history of advocacy, meme-making, and evangelism.
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