CASS

6. Related Work

Work on decentralizing the orchestration of composite web services [17] demonstrated significant performance improvements in terms of increased throughput, scalability and response time. First, the absence of centralized coordination eliminates a potential bottleneck and improves concurrency.
Second, by distributing the data, the network traffic is reduced and transfer time is improved. The paper proposes an algorithm to partition a centralized BPEL specification. The authors acknowledge the decentralization increases the complexity of the system, especially regarding error handling. They therefore introduce a runtime infrastructure to handle error propagation and recovery. The CASS model relates to the work presented in the paper in that the coordination aspects are deployed in a decentralized way. However, partitioning a centralized BPEL specification limits the range of possible orchestrations to the constructs supported by BPEL, which are client-centric. This means that the orchestration is only valid from the perspective of a given client. As BPEL targets long-running web service orchestrations, there is no support for the dynamic deployment and refinement of service compositions.
AO4BPEL [18] propose an aspect-oriented approach to web service composition. The paper identifies two main limitations of BPEL. First, the hierarchical modularization of the composition specification does not allow the encapsulation of some aspects of the orchestration such as exception handling, authentication or business rules. Second, BPEL does not support the dynamic adaptation of the composition logic. AO4BPEL uses a dynamic AOP extension to BPEL to improve the modularity and the flexibility of web service composition specifications. AO4BPEL addresses some of the issues the CASS model tackles. However, AO4BPEL does not provide the capability to refine services themselves. It improves the modularity and flexibility of the composition glue code, but is limited in the adaptations it supports by the web service interfaces. By allowing the dynamic refinement of web service instance interfaces, the CASS model supports much more powerful web service composition refinements. Moreover, the CASS composition deployment specifications are decentralized and are not limited to client specific requirements.
The Web Service Management Layer (WSML) [19] takes advantage of the dynamic AOP language JAsCo [20] to provided a highly dynamic client-side web service management environment that decouples service management concerns from the client applications. WSML does not address web service composition.