An abstract model for service provision, search and composition

Service-oriented computing, cloud computing, and web services composition mark cornerstones of a paradigm shift in software systems engineering. The general new idea is to use as much as possible services that are made available by others, mostly disseminated via the web. In this paper, we present an abstract model for clouds as federations of services together with a specification of semantics and quality characteristics. For the services as such we adopt the abstract model of abstract state services, which is based on views on some hidden database layer that are equipped with service operations. For the semantics we adopt types for in- and output, pre- and post-conditions, and a description of functionality within an operations ontology. In addition, quality characteristics capture performance, costs, availability, etc. On the basis of this model of clouds, users may conduct a (web) search for usable services, extract service components, and recompose these components. The quality characteristics can be used to optimise the selection of usable services.