Semi-automated service composition using visual contracts

Services provide access to software components that can be discovered dynamically via the Internet. The increasing number of services a requesters may be able to use demand support for finding and selecting services. In particular, it is unrealistic to expect that a single service will satisfy complex requirements, so services will have to be combined to match clients' requests. In this paper, we propose a visual, interactive approach for the composition of services, in which we describe the requirements of a requester as a goal which is matched against multiple provider offers. After every match with an offer we decompose the goal into satisfied and remainder parts. We iterate the decomposition until the goal is satisfied or we run out of offers. Finally, the individual offers are combined into a single combined offer and shown to the requester for feedback. Our approach is based on visual specifications of pre- and post conditions using the theory of graph transformations systems as a formal background.