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W3C Publishes WS Choreography Requirements Draft

Showing that it has been plugging away since the high-profile exit of Microsoft in March, the World Wide Web Consortium's (W3C) Web Services Choreography Working Group published the first public working draft of Web Services Choreography Requirements 1.0 Tuesday.

When Microsoft chose to throw its support behind the OASIS Web Services Business Process Execution Language (BPEL) Technical Committee, many industry watchers saw evidence of a growing rift -- not just between heavy-weights like Microsoft and Sun, but between the OASIS and W3C standards bodies themselves.

But a meeting between the BPEL Technical Committee and WS Choreography Working Group in May seemed to signal that the two organizations were ready to put that potential trouble behind them. The working group's draft Tuesday, may be a further sign, as it identifies BPEL as a component among the Choreography programming languages in the document.

Choreography is currently one of the most important issues facing Web services, according to W3C. Choreography describes interactions among Web services -- especially with regard to the exchange of messages, their composition, and the sequences in which they are transmitted and received. The interactions can take place among groups of services which make up a larger, composite service, or which interact across organizational boundaries to obtain and process information.

But how are messages to be exchanged and sequenced so that they arrive at the appropriate destinations at the appropriate times? The new working draft is intended to help answer those questions by describing a set of requirements for Web services choreography based around a set of representative use cases, as well as general requirements for interaction among Web services.

"Web Services Choreography concerns the interactions of services with their users," the working group said. "Any user of a Web service, automated or otherwise, is a client of that service. These users may, in turn, be other Web services, applications or human beings. Transactions among Web services and their clients must clearly be well defined at the time of their execution, and may consist of multiple separate interactions whose composition constitutes a complete transaction. This composition, its message protocols, interfaces, sequencing, and associated logic, is considered to be a choreography."

The draft is built around 11 member-submitted use cases, consisting of descriptions of interactions, which take place across one or more system boundaries, involving one or more users and services. The use cases range from descriptions of "Client Server" Web services (in which one service is the client and the other the server), to descriptions of systems that allow devices to connect to a network, be recognized and installed into that network, and then bound to other devices on the network to form a unique, composite device. Others describe services which bring together travel agents, service providers and credit card companies to create a vacation booking service.