Provided and requested services in the specification and design of services and service-oriented architectures

Abstract In service-oriented systems and service-oriented architectures (SOA), system components offer services and request services. Well-known examples of this paradigm are layered architectures where each layer provides services to its layer above and requests services from its layer below. This concept is generalized and extended to SOA designed in terms of the flow of services between the system components. We end up with the generalization of the concept of layered architectures where service components are composed in terms of their provided and requested services. Key aspects are service access protocols, which define the rules for getting access to a service. Service-oriented systems and SOA are graphically represented by service flow diagrams. A general approach to the formal specification and concurrent composition of service-oriented system component specifications is worked out based on a formal system model capturing services, service-oriented components, and SOA. We treat, in particular, formally the situation where concurrent composition of components and their services leads to feedback cycles in architectures. Typically, if in a SOA for some components their services are error prone, the system works properly at least until some error occurs. To handle such cases, the calculus is extended to specific rules for input assumptions which identify erroneous situations. Moreover, we study feature interactions between families of services offered by service components as well as the refinement and refactoring of services and service architectures.