Extending BPEL for Run Time Adaptability

Abstract

The existing Web service flow (WS-flow) technologies enable both static and dynamic binding of participating Web services (WSs) on the process model level. Adaptability on per-instance basis is not sufficiently supported and therefore must be addressed to improve process flexibility upon changes in the environment. Ad-hoc process instance changes can be enabled by swapping participating WS instances, by modifying port types of the partners to be invoked, and by changing process logic. In this work, we address the problem of dynamic binding of WSs to WS-flow instances at run time, i.e. the ability to exchange a WS instance participating in a WS-flow instance with an alternative one. The problem is additionally complicated by the fact that the execution of a process depends on its deployment. We describe the "find and bind" mechanism, and we show its representation as a BPEL extension. We discuss the benefits that could be gained and the disadvantages it brings in. The mechanism extends and improves the existing process technologies. It facilitates a precisely controlled policy-based selection of WSs at run time and also provides for process instance repair, while maintaining simplicity. We also discuss a prototypical implementation of the presented functionality.