Behavioral service substitution: analysis and synthesis

Service-oriented computing has emerged as an acknowledged paradigm for developing complex and non-monolithic systems of different kinds. The paradigm allows different organizations to aggregate several simple services to form a composition of communicating entities in the system. Naturally, services in such a system are subject to change and adaptation over time. Service-oriented computing provides the support for service evolution by allowing one service to be substituted by other services. From the viewpoint of a single service, the composition of the other communicating services in the system is regarded as partner. Substituting one service by another should guarantee to preserve every partner that is correct according to a correctness criterion of composition in the overall system. The aforementioned substitution criteria impose difficulties for a service designer, such as a domain expert, to perform analysis and synthesis tasks on service substitution. Due to the complexity of service interaction in the system, it is not straightforward for a service designer to foresee every partner and every substitute for the given service under a specific correctness criterion. In this thesis, we develop an approach that shall assist a service designer to perform analysis and synthesis tasks on service substitution in a way that every partner of a given service must be preserved under substitution. We model a control flow of services that describes the ordering of asynchronously communicating events over an implicit unordered message buffer. We study the behavioral aspect of correct interaction between services and concentrate on two variants of deadlock freedom as correctness criteria of service composition. The main contribution of this thesis is an approach for characterizing the set of all substitutes for a given service. The central idea of the approach is to systematically investigate the relationship between a service and all its partners under a given correctness criterion. We employ this relationship to synthesize from a given service its canonical partner and its canonical substitute with respect to all partners. A service that refines the canonical substitute for a given service is regarded as a substitute for the given service if the set of all its partners includes every partner of the given service. With the canonical substitute of a given service, we identify a specific subset of the set of all substitutes for the given service, each of which has exactly the same set of partners as that of the given service. Parts of the results in this thesis have been established upon previous works on service substitution and correctness of services and their composition. Consequently, we can also combine our results with the related existing techniques to perform more sophisticated analysis and synthesis tasks on service substitution.