On Solving QoS-Aware Service Selection Problem with Service Composition

Runtime QoS-aware service selection is difficult because the number of web services providing similar functionality is large and constantly changing, and, even more challenging, due to the complicated structure of composite services. This paper proposes an efficient divide-and-conquer approach for service selection based on a high-level abstract model for service composition. The service composition model is recursively defined with (1) abstract control-flows of five general constructs ("Sequence", "Switch", "While", "Flow", and "Pick"), and (2) extended data-flows with constructs of "AND" and "OR". Based on this service composition model, a QoS model, which supports non-linear QoS aggregation, is proposed. Therefore, complex control-flows are handled in an integrated way without separating and merging multiple execution paths, and interface constraints are captured in form of data-flow declaration. This approach allows to divide the original service to several smaller services, which are then solved separately by a recursive branch-and-bound algorithm Experiments show that the proposed approach is efficient and scalable for runtime service selection, and better handles complicated structure of service composition than existing approaches.