Optimal Compensation for Hierarchical Web Services Compositions Under Restricted Visibility

Over the years, the notion of transactions has become synonymous with providing fault-tolerance, reliability and robustness to database systems. To extend the same transactional guarantees to new and evolving paradigms, such as Web service, the transactional mechanisms must first be adapted to the distinguishing characteristics of Web services, mainly composability, long-running nature, and privacy and security concerns. Composability refers to the ability to form new composite services by combining the functionalities of existing services. Due to their long-running nature, compensation based mechanisms are usually preferred to provide transactional guarantees for Web services. Compensation requires access (visibility) over the execution details of the services in the composition. However, such visibility may not always be feasible in a compositional context where component services are provided by different providers across organizational boundaries, with very strong privacy and security constraints. This paper looks at compensation options for Web services in a hierarchical composition. Multiple compensation options may be available for a composite service both at the same level and at different levels of the hierarchy. This paper shows how to find an optimal compensation option under restricted visibility.