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New W3C standard choreographs Web services dance

Three or more e-business companies have Web services and they want to connect, so what do they do? Send each other their WSDLs and hope for the best?

That is probably not the best practice, according to Steve Ross-Talbot, co-chair of the W3C WS-Choreography Working Group, which has released the first draft of its Web Services Choreography Description Language (WS-CDL) 1.0.

Borrowing a term from the world of dance, WS-CDL is intended help choreograph the Web services ballet, Ross-Talbot explained to XDT in an e-mail from his base in the U.K. where he is chief scientist at Enigmatec Corp.

WS-CDL describes and sets rules for how different Web services components will interact, according to the W3C. It provides for sequencing and also offers a "flexible systemic view of the process." The W3C positions WS-CDL "as a necessary complement to BPEL, Java, and other programming languages which describe one endpoint on a transaction, rather than the full system."

Asked what the choreography standard brings to the Web services dance, Ross-Talbot responded: "What has been missing has been the descriptions of how Web services work together in a peer-to-peer and a centralized fashion. WS-CDL is all about peer-to-peer."

He said the choreography standard makes it possible for three or more Web services to talk to each other without a broker to orchestrate the interaction.

Asked for hypothetical examples of how WS-CDL would be used in e-business, Ross-Talbot said: "It might be used by a vertical standards organization such as fixprotocol.org [98% of equities trading goes through this standard] to describe how the participants in a financial transaction interact with one another."

Noting that old-fashioned business transactions relied on contractual or at least handshake rules and agreements, Ross-Talbot pointed out that the WS-CDL will play a role there, too. The standard agreement on how the Web services will operate together helps to assure that the rules are followed.

"You might use the WS-CDL description as an input into a tool that polices or enforces the agreed behavior at any one of the endpoints [or participants] that require it," he explained. "This way the enforcement is distributed in a peer-to-peer-like fashion without any single point of control ever being exerted. The conformance to the WS-CDL guarantees that everything works correctly."

The standard is needed because despite the hype, Web services are unlikely to magically connect to one another so that e-business just happens. When businesses exchange information, Ross-Talbot explained, "the dance they follow is pretty well agreed to in advance and not done ad hoc."

So in the e-business theater there is now a way to do choreography so that the dancers don't accidentally fall off the stage.

More information on Web Services Choreography Description Language (WS-CDL) 1.0 is available at http://www.w3.org/TR/2004/WD-ws-cdl-10-20040427/

About the Author

Rich Seeley is Web Editor for Campus Technology.

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