The Evaluation Method For Execution Environment Usability Of Composite Service Focused On Evironmental Self-adaption

The quality of composite service always can not meet the requirement because of the dynamic change of the execution environment. To solve the problem, our group has designed a self-adaptation engine to make policies based on the environment changes to realize the active adaptation during execution. But the environment information can not be used to support the self-adaptation directly. It must be changed into environment usability to serve the self-adaptation, which is called an environment usability evaluation and the focus of this paper is just about the evaluation method. In this paper, there are several theoretical and practical problems to be solved:the description and treatment for environment change events; the modeling for the environment failure, the execution of composite service and the composite service combined with the environment; different calculation methods for different quality constraints; the sharing of evaluation results and the trigger mode for self-adaptation.To solve these problems, this paper proposes two different evaluation methods oriented local and global quality constraints. In the local usability evaluation, the change events of service quality are defined and classified based on the execution status and constraints of the composite service and the evaluation rules are given to each condition. In the global one, this paper extends the meta-model of WSDL to describe the execution environment. On the basis of that, this paper models for the composite service and the failure status of the execution environment, and then combines them all to get a Petri Net model about the execution process affected by the environment. By way of the ability to analyze system performance from Petri Net, this paper calculates the execution time of the composite service, and then obtains the usability evaluation result by the comparison between the execution time and the constraints. Besides, this paper provides some data to describe the environment failure status, and then calculates the execution failure rate which is caused by environment failure to verify the relationship between the environment and the quality of composite service. Finally, this paper describes how to develop a usability evaluation component based on service bus ServiceMix.