Service composition offers a way to expand the ability of the single service and im-plement service reuse. It allows a distributed application to be constructed through the combination of other existing services, and this composition offers added value to the original services. However, the service discovery and selection mechanisms are static and not flexible in existing approaches to service composition, and the end-to-end QoS of a composite service can not always be ensured. This chapter puts for-ward a Multi-agent based QoS-aware Service Composition solution (MQSC), which not only provides a mechanism for dynamic service composition but also can ensure the end-to-end QoS of the composite service. Compared with the existing methods for using multi-agent systems in service composition [6, 8, 20, 25], our solution has the following characteristics:
1. Executing automatically: Once the task is submitted to the PA, the process of service composition including service search, service selection and service exe-cution will be executed automatically.
2. Deciding dynamically: On the one hand, the DA decides the optimal service composition plan dynamically based on the ACS. On the other hand, the EA decides their behaviors dynamically according to the plan scheduling algorithm.
3. Fault recovering: The management function of the MA guarantees that the sys-tem has fault tolerance.
4. Saving resources: The basic execution patterns make the system avoid creating redundant agents so as to alleviate burdening the network.
5. Allowing distributed and parallel execution: If there are multiple parallel paths in the SCG, multiple EAs will travel these paths in parallel without waiting. This avoids the frequent communication between agents presented in [6].
In this chapter, we assume that the Task Graph has been given and focus on service search, service selection and service execution. Thus, how to get the Task Graph from the general requirements submitted by customers is one of our future works.
In addition, heuristic information could improve the performance of the ASC based algorithm, so other heuristic methods would be also considered in our future work.
Acknowledgements
This work is supported by the National Natural Science Foundation of China under Grants No. 90604004 and 90412014, Jiangsu Provincial Natural Science Foundation of China under Grants No. BK2007708 and Jiangsu Provincial Key Laboratory of Network and Information Security under Grants No. BM2003201.
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Flexible Workflow Management in Service Oriented Environments
Birgit Hofreiter and Christian Huemer
AbstractEver faster changing market conditions require businesses to frequently adapt their business processes and the underlying workflow systems. Service-oriented architectures are said to deliver this flexibility by loose coupling. In this chapter we provide a survey on realizing flexible workflows on top of service ori-ented architectures. We show how orchestrations and choreographies may be imple-mented by state-of-the-art web services technology. The role of agents in realizing workflows among services is discussed. Furthermore, we discuss service provision in dynamic environments, when partners are dynamically bound to the workflow and when changes to the workflow schema happen.