News

Time to rethink XML schema?

• By Jack Vaughan
• June 16, 2004

It is probably too early to say for sure, but it appears that Web services standards are quietly changing the world of development. Web services represent a detente of sorts between two big developer camps -- IBM and Microsoft.

The detente only affects development efforts that embrace XML, but that covers an increasingly large swath of developers. IBM and Microsoft are far from alone in standard Web services; Oracle, Computer Associates, BEA and others have agreed to support this technology paradigm, which is spurred on in no small part by the efforts of the Web Services Interoperability (WS-I) Organization.

Programmers Report recently spoke with Thomas Glover, WS-I president and chairman, who also works at IBM as program manager for Web services standards. Glover outlined current work at WS-I, which is marked by progress on a Basic Profile 1.1 as well as a Basic Security Profile.

Also of interest, the group is considering ways it can promote the state of the art in XML schemas. At the heart of the XML promise has always been the schema that describe how XML should be handled. If these schema work, XML works across machines, systems and ages.

Glover said recent work on the Basic Profile has been in the nature of fixes. Agreements on how to handle attachments have also been achieved. His group is "almost done with the security profile," Glover noted. Specifically, this profile will address SOAP messaging and transport security. The group has begun to work more closely with the OASIS standards group on this. The final WS-I profile is expected to include Username and X.509 token types. SAML and XRML Token types are being considered.

All this is good. Profiles are useful as they distill the experiences of bleeding-edge implementers. To make one Web service talk to another is still something of an accomplishment, and using WS-I profiles can save a lot of time on the old learning curve.

But what of schema? The World Wide Web Consortium (W3C) has worked hard to standardize this part of XML. Apparently, even though XML is five years old, this is still a maturing area. Glover told us that his group is organized to help users surmount problems, and that feedback indicates schema representation is one of them.

"A lot of people are having problems using XML schema representation. They are building schemas that define payload. The problem is that the spec [from the W3C] is extremely large. At times, it offers fundamentally different ways to describe the same thing," said Glover.

He noted that the W3C is working right now to fix "errata," but suggests that WS-I may be able to be helpful in establishing useful profiles for schema. "There are areas where it could be made more precise," Glover said.

Is perfection the goal? No, not really. The WS-I profile process is about "iteratively reducing the set of problems" developers have to deal with, said Glover. "The profiles offer more clarity. Over time, the guidance we give will get better and better."