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Choreography tools deliver on promise of SOA

New choreography tools for service-oriented architectures enable developers to define how multiple parties can collaborate in a peer-to-peer environment.

As organizations deploy their applications to interact with a range of trading partners and external organizations, standards and tools are emerging to help them better define the rules of engagement.

Pi4 Technologies Ltd. recently unveiled the first version of a new set of choreography tools for defining how multiple parties collaborate in peer-to-peer, service-oriented business transactions.

The Pi4soa tools suite, which includes a choreography description editor and a choreography simulator, is an open source implementation of the Web Services Choreography Description Language (WS-CDL) being developed by the World Wide Web Consortium (W3C). Pi4soa is based on the Apache 2.0 license agreement and is available as an Eclipse plug-in.

"One of the problems is that people build services from a service-centric perspective," said Steve Ross-Talbot, co-chair of the W3C's Web Services Choreography working group and CEO of U.K.-based Pi4. "They look at individual services and not the more holistic process view of all services."

Aligning service-oriented architectures (SOAs) with business processes has been the goal of orchestration and choreography standards such as the Web Services Business Process Execution Language (WS-BPEL) and WS-CDL.

The difficulty with SOA and Web services, Ross-Talbot said, is that "they don't always meet business requirements. WS-CDL would certainly improve this today."

While WS-BPEL allows existing Web services to be orchestrated into composite services, WS-CDL goes a step further and describes the relationships between these composite services in a peer-to-peer environment.

For more information

Check out this interview with Steve Ross-Talbot comparing WS-CDL and WS-BPEL


Learn more about WS-BPEL

In a March 2005 interview with, Ross-Talbot said: "What choreography says is 'I have a bunch of services; how do I write down what those services should do to engage with each other?'" "What I want to do is write down, from a high level, what's the exchange of messages that occur [between organizations] to buy a widget [for example]."

The Pi4soa WS-CDL editor allows developers and architects to create messages and documents that conform to the WS-CDL specification. The simulator executes test scenarios against various choreography descriptions based on a pre-established sequence of messages that need to be exchanged between two parties.

"When messages are seen as out of sequence, errors are flagged by the tool so you can either adjust the WS-CDL description to conform to the messages in the log or change the offending service/application to conform to the WS-CDL description," Ross-Talbot said.

Organizations currently building out their SOA or Web services products stand to benefit from WS-CDL implementations today, Ross-Talbot said. "It will act as a 'blueprint' for the SOA and provide them with huge benefits in terms of design and in terms of ongoing compliance to a design."

While WS-BPEL is widely supported by commercial tools and business process management products today, WS-CDL is still an emerging standard and is backed by several vendors, including Oracle Corp., Sun Microsystems Inc., Adobe Systems Inc., Nortel Networks Ltd. and Novell Inc.

Once WS-CDL reaches the Candidate Recommendation (CR) stage, the working group will call upon vendors to demonstrate that implementations of the specification "work together and exercise all of the main features of WS-CDL," Ross-Talbot said.

WS-CDL is expected to be ratified by the end of the year.

"But of course things get used by people in advance of this," he said. "Essentially, after CR it [WS-CDL] is real and tangible."

Dig Deeper on Topics Archive

Dancing with Web services: W3C chair talks choreography As companies embrace service-oriented architecture, the Business Process Execution Language (BPEL) continues to gain traction as a means to weave Web services into meaningful business processes. While BPEL allows existing services to be orchestrated into composite services, the Web Services Choreography Description Language (WS-CDL) goes a step further and describes the relationships between services in a peer-to-peer scenario. In this interview, Steve Ross-Talbot, co-chair of the W3C Web Services Choreography Working Group, describes choreography and how it differs from orchestration in the context of Web services. He compares the WS-CDL and BPEL specifications, looks at how the two can work together and describes four tools that will be needed to work with WS-CDL.

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