XML Schema Catches Heat

After more than two years of development, the World Wide Web Consortium could be only weeks away from releasing its long-awaited XML Schema specification.

After more than two years of development, the World Wide Web Consortium could be only weeks away from releasing its long-awaited XML Schema specification. But despite its release, the specification, which is designed to automate data exchange between companies, is coming under fire.

Now in the final review phase by W3C Director Tim Berners-Lee, the specification, according to critics, is far too complex—so complex that it has driven several XML experts to create alternative and lighter-weight schemas. Furthermore, some W3C insiders are even calling for future versions to be incompatible with this first release so as not to repeat what they say are the flaws of the first version.

XML Schema has been one of the most watched standards efforts of late. The schema expresses shared vocabularies and defines the structure and content of XML documents. XML Schema is expected to make data exchange among businesses cheaper and easier than what is possible using Document Type Definitions.

The comment period for XML Schema ended last week. The spec now lies with Berners-Lee, who will determine if any technical issues raised should prevent its release. W3C officials expect a decision within weeks.

"XML Schema provides more robust tools than are available today," said Leo Massarani, chief technology officer of The Thread, an Internet-based network in New York that helps fashion and apparel companies create customized Web-based supply chains.

According to Massarani, files often have to be printed and faxed between destinations because there has been no common way to describe things such as orders or items. "Right now, there are 20 or 30 different systems used and multiple releases within that, and no common standard. Its a real nightmare," he said.

Henry Thompson, one of the editors of XML Schema, said the high level of interest is not surprising.

"People figured out the Web meant they could make money from their data in a way they never could before," said Thompson, a W3C Fellow in Edinburgh, Scotland. "But to get that money, they had to have a way to move their data over the Web."

But some say the working group tried to accomplish too much, which resulted in an extended development process and an overly complex spec.

"The main problem I have with it is its too complicated," said James Clark, an XML expert in Bangkok, Thailand, who launched his own schema effort, called Trex, in December. "Its fine if youre a huge company like Microsoft [Corp.] or IBM. They can just add more developers."

Trex, which Clark submitted to the Organization for the Advancement of Structured Information Standards, is simpler and more modular, as it focuses just on the validation of XML documents. A similar effort, Relax, was started late last year by schema working group member Makoto Murata. Murata, who works with the International University of Japan Research Institute and IBM in Tokyo, also dissatisfied with the W3Cs direction, said the schema group was focused more on benefits to vendors than on the technology, unlike the original XML working group.

Clark and Murata recently merged their efforts under OASIS, in Billerica, Mass. Clark hopes they can produce a first draft in two to three months.

Another alternative, called Schematron, was started in October 1999 by working group member Rick Jelliffe, who represented Academia Sinica Computing Centre, in Taipei, Taiwan, until this month.

Despite the controversies, many are supporting XML Schema, including Microsoft, IBM and Oracle Corp. Microsoft last week announced a technical preview of its XML parser supporting schema. The Redmond, Wash., company also will include XML Schema in the second beta version of Visual Studio.Net, which will be given to attendees at Microsofts TechEd conference in June.

"The reality is Schema is actually trying to solve a very hard problem," said David Turner, senior program manager for Microsoft, adding that XML tools will shield users from its complexity. "The majority of people involved do believe the end result is useful, and there is no doubt it is necessary."