Dynamic Replanning of Web Service Workflows

The composition of Web Services to workflows is one of the major challenges in the area of service-oriented computing. To meet the business and user requirements, it is crucial to manage the quality of service (QoS) of Web Service workflows. In our approach, we calculate the execution plan of workflows on the QoS attributes ex ante based on predictions. However, due to the volatile nature of the Internet and the web servers, the runtime behavior of Web Services is likely to differ from the predictions. Therefore, we propose replanning as a mechanism to adapt the execution plan to the actual behavior of already executed services by a dynamic service selection at runtime, ensuring that the QoS and cost requirements will still be met. In this paper, we discuss replanning strategies, show how replanning leads to cost-savings in most cases, and evaluate the additional overhead caused by the adaptation of the execution plan at runtime.