Managing QoS Degradation of Component Web Services in a Dynamic Environment

In Services Oriented Computing, a composite web service is a value-added service composed of loosely coupled, independent, and distributed component web services. Component or partner web services jointly contribute to fulfil functional as well as non-functional requirements of users of a composite web service. One of the fundamental challenges in Services Oriented Computing is to ensure that a composite web service is flexible enough to react to changes (QoS degradation) in its partner web services at the time of execution. In this context, it is important that the time to adapt to changes should not be significant. Several solutions exist for run-time monitoring of partner web services so that clients can replace them with better alternatives when their QoS values degrade. But these solutions follow either a reactive approach (which is time consuming), or a prediction-based proactive approach (again time consuming, and moreover predicted events may never happen). This article proposes a solution using a publish/subscribe mechanism which is distributed between web service clients and the service providers, and follows a proactive preventive approach. It uses mobile agents to communicate partner web service's QoS status to its clients just in time, in order to decide to choose an alternative in case the QoS values are not satisfactory. The prototype is implemented using JAVA and Java Agent DEvelopment framework (JADE) programming languages. The experimental results show effectiveness of the proposed approach when compared with a static approach (the benchmark), as well as with a reactive solution. Moreover, the framework performs well even in the wake of the increasing levels of QoS degradation of partner web services.