Binding and execution of web service compositions

Web services enable the design, integration, composition, and deployment of distributed and heterogeneous software. While most syntactic issues in composition have been taken care of somewhat satisfactorily, several semantic issues remain unresolved. In this paper, we consider issues relating to binding and execution of composite services. A Web service composition or composite activity consists of a set of (basic or composite) activities with some ordering constraints. In general, an arbitrary collection of execution instances of the individual activities may not constitute an execution of the composite activity; the individual execution instances must be "compatible". In this paper, we propose (a) a simple formalism to express the compatibility requirements in a composition, and (b) a methodology for (i) the selection of a composite service provider for a composite activity and (ii) the selection of (other) service providers for the constituent activities of the composite activity, to ensure an execution of the composition satisfying the compatibility requirements.