Service Choreography and Orchestration with Conversations

Service oriented computing provides technologies that enable multiple organizations to integrate their businesses over the Internet. Typical execution behavior in this type of distributed systems involves a set of autonomous peers interacting with each other through messages. Modeling and analysis of interactions among the peers is a crucial problem in this domain due to following reasons: 1) Organizations may not want to share the internal details of the services they provide to other organizations. In order to achieve decoupling among different peers, it is necessary to specify the interactions among different services without referring to the details of their local implementations. 2) Modeling and analyzing the global behavior of this type of distributed systems is particularly challenging since no single party has access to the internal states of all the participating peers. Desired behaviors have to be specified as constraints on the interactions among different peers since the interactions are the only observable global behavior. Moreover, for this type of distributed systems, it might be worthwhile to specify the interactions among different peers before the services are implemented. Such a top-down design strategy may help different organizations to better coordinate their development efforts. This type of distributed systems can be modeled as a composite Web service that consists of a set of peers that interact with each other via synchronous and/or asynchronous messages [3]. A conversation is the global sequence of messages exchanged among the peers participating to a composite Web service [2]. A choreography specification identifies the set of allowable conversations for a composite Web service. An orchestration, on the other hand, is an executable specification that identifies the steps of execution for the peers. This conversation based modeling framework leads to the following interesting problems: realizability, synthesis, conformance, and synchronizability [4]. A choreography specification is realizable if the corresponding conversation set can be generated by a set of peers [6, 9]. This step is necessary to guarantee that the choreography specifications that are developed in a top-down manner are implementable. A related problem is automated synthesis of peer implementations from a given choreography specification. Another interesting problem is investigating the conformance between orchestration and choreography specifications. An orchestration specification conforms to a choreography specification if the global sequence of messages generated by the orchestration is allowed by the choreography specification. Finally, synchronizability analysis [5, 10] investigates the effects of asynchronous vs. synchronous communication to improve the