XML 'scheming' its way into e-business

[Ram Kumar <rkumar@msi.com.au>]

XML 'scheming' its way into e-business
By Timothy Dyck, eWEEK
30 May 2001

Earlier this month at the Tenth International World Wide Web Conference in
Hong Kong, XML took its biggest step forward since the document format was
first standardised in February 1998.
At the conference, the World Wide Web Consortium released XML Schema as a
W3C Recommendation, finalising efforts that started in 1998 to define a
standard way of describing Extensible Markup Language document structures
and adding data types to XML data fields.

Now that it is finally out, the long-delayed XML Schema standard will
catalyse the next big step in XML—-allowing cross-organisational XML
document exchange and verification.

Just as discovery of the Rosetta stone in 1799 provided a way to fix the
meaning of Egyptian hieroglyphs so they could be understood across the gulf
of two millennia, XML Schema provides a way for organisations to fix the
meaning of XML documents so they can be understood across the gulf of
organisational boundaries and otherwise incompatible IT architectures.

As a result, XML Schema will be a cornerstone in the new e-commerce
architecture that we are collectively building and will be a vital component
for making business exchanges and other loose associations of trading
partners possible.

The arrival of XML Schema, more than three years after XML itself, has left
many chafing at the bit (and others, such as Microsoft, running off in their
own direction implementing and shipping products based on prestandard
efforts), and the market is now more than ready for this standard to take
hold.

However, XML Schema's long development cycle gave vendors time to understand
the specification and start writing compliant software, and we are now
seeing the rapid release of XML Schema-compliant (or soon-to-be-compliant)
authoring tools and servers.

A little of everything
That long, committee-driven development cycle also resulted in a
specification that has a bit of everything in it, and fully compliant XML
Schema parsers will have to be complex pieces of software to support all the
options the specification allows.

Fortunately, XML Schema documents have to reference only the functionality
they need, and the more complex options in XML Schema, such as null elements
and explicit types, may just fade away through disuse.

The W3C recently published a recommendation on how to group Extensible HTML,
the consortium's replacement for HTML, into well-defined subgroups so XHTML
browsers (such as those in cellular phones) can clearly define which parts
of the language they support and which they don't.

Something similar is a possibility for XML Schema if the full specification
proves too difficult to implement for some vendors (although large players
such as IBM, Microsoft and Oracle are moving ahead full speed with plans to
support the full specification as published).

Over the next few years, eWEEK Labs predicts XML Schema will become integral
to the way that many companies exchange information.

XML Schema is clearly needed in today's e-business arena; it makes sense and
is the logical next step forward for XML, the single most important enabling
technology of business-to-business communication.
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What XML Schema does

The XML Schema specification consists of two parts.

Part 1 describes a language (the XML Schema Definition language) that is
used to describe the high-level structure of an XML document.

Part 2 describes the list of allowable data types that can be used by the
XML Schema Definition language (and thus in XML documents themselves).

It's very important for developers to understand that XML Schema documents
are actually XML metainformation: They describe the structure of XML
documents and don't contain end-user data themselves.

By using the XML Schema Definition associated with an XML data stream, an
XML parser can automatically verify not just the syntax of the XML data but
also its structure and logical correctness—-a big step forward. XML Schema
replaces the obscure and far less-powerful XML Document Type Definition
standard.

For example, using XML Schema, companies can now detect if received XML
files have missing data, data that's been improperly formatted (such as
dates with only two-digit year values or fields with words entered where
there should be numbers) or data that's obviously wrong (such as numbers
that are clearly too large or too small to possibly be valid).

The range of characteristics that XML Schema defines is very comprehensive
and includes a large selection of basic data types, such as integers,
floating-point numbers, strings, times and dates; it also includes ways to
constrain values to valid data ranges or to lists of valid values, the
ability to define default values for missing data and the ability to make
data elements required.

XML also defines complex types composed of groupings of simple types (such
as an "address" type).

Regular expressions can be used to check for valid data, and XML Schema
documents can inherit from and then partially override the behaviour of
other XML Schema documents for object-oriented development.

XML Schema does not provide a way to see whether values that look correct
actually are correct (by checking against values in a database, for
example), but vendors such as Data Junction are now starting to provide this
capability.

Because it provides a way for organisations to share high-level definitions
of how XML data should be structured, business exchanges are grabbing up XML
Schema like there's no tomorrow.

Centralised repositories of XML file format information, such as Microsoft's
BizTalk, are now accepting submissions of industry-specific XML document
definitions in XML Schema format.
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Other XML standards ready to roll
As XML has progressed down the technological road since its introduction in
1996, it has steadily gained momentum, to the point where most other World
Wide Web Consortium standards are now based on Extensible Markup Language.
But for the last two years, the giant, wide-body truck that has slowed its
progress has been the development of XML Schema as a standard.

Now that the W3C has finally gotten XML Schema into gear, what's next for
XML?

eWEEK Labs believes several core XML technologies will probably become
standards (or Recommendations, as the W3C calls them) this year and, for the
most part, all will help improve the interoperability of XML-based data and
applications. Also, not surprisingly, most of these related technologies
were initially proposed around the same time as XML Schema.

The XML Information Set, which is expected to reach recommendation status
next month, will provide a common reference set for defining abstract
objects such as elements within a document. The main goal here isn't to
provide a definitive set of definitions but to provide a base that will
improve interoperability among XML tools and applications.

Later this year, several technologies pertaining to XML linking--Xlink,
Xbase and Xpointer--should become standards or reach candidate status. All
these technologies deal with hyperlinking within XML documents, in a manner
similar to the way Uniform Resource Indicators work. All three will enable a
much more complex and multilayered linking than what is currently possible
in HTML and XML.

Whereas the other technologies listed here have been around for almost two
years, XML Query was introduced just this year and is probably at least a
year away from becoming a standard. As the name suggests, one of the goals
of XML Query is to provide the same type of advanced capabilities that SQL
queries have provided for standard databases.

The power here is that, although SQL queries are limited to collections of
structured data, XML Query will make it possible to build queries based on
collections of XML files that might contain unstructured data, such as
documents or Web pages.

Evolution of XML Schema
The following sites provide tools and resources for XML Schema and its
integration with other systems

— February 1999 W3C publishes first set of requirements for upcoming XML
Schema effort

— May 1999 XML Schema first working draft published

— September 2000 XML Schema seventh working draft published

— October 2000 XML Schema Candidate Recommendation published

— March 2001 XML Schema Proposed Recommendation published

— May 2001 XML Schema published as a W3C Recommendation

Source: W3C and Organisation for the Advancement of Structured Information
Standards