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cl: A Language for Formally Defining Web Services Interactions
Frolund, Svend; Govindarajan, Kannan
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Abstract: Web services have emerged recently as a distributed computing paradigm of choice for loosely-coupled computing. Current web services standards such as SOAP, and WSDL provide rudimentary mechanisms for defining interaction amongst services that may be located in different organizations. While WSDL provides the definitions for the entry-points of a service, in many cases, the interactions between services has more structure than can be described by just the definition of entry points. In particular, the sequence of interactions often is an important component of interactions between services. In current web ser vices standards, the notion of sequencing is handled by the workflow definitions provided by proposals such as BPEL4WS. Although workflow definitions are clearly powerful enough to express all possible sequences of message exchanges between services, our approach is different. Our contention is that sharing workflow definitions across services will enable inter-operability, but leads to tighter coupling amongst the services. We propose a conversation definition language as a simple, yet powerful, way to define web services interactions. Our definitions have no executable logic in them, just as traditional interfaces do not have any implementations in them. The main idea behind cl is to explicitly define the permissible message exchanges over time (conversations) between web services. We also introduce the notion of choice as a key enabler in expressing the externally visible behavior of services. We provide semantics for such conversation definitions in terms of the potential traces of documents exchanged between the services. We outline some of the essential properties of such conversation definitions, compare with other similar approaches, and discuss potential directions for further research.
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