Web Services and service-oriented architectures (SOAs) represent a new paradigm for building distributed computing applications. In recent years, they have started to play a critical role in numerous e-Science and e-Commerce applications. The advantages of Web Services, such as their loosely coupled architecture and standardized interoperability, make them a desirable platform, especially for developing large-scale applications such as those based on cross-organizational service composition.

However, the Web Service technology is now facing many serious issues that need to be addressed, one of the most important ones being the dependability of their composition. Web Service composition relies on individual component services and computer networks, particularly the Internet. As the component services are autonomous, prior to use their dependability is unknown. In addition to that, computer networks are inherently unreliable media: from the user’s perspective, network failures may undermine the dependability of Web Services. Consequently, failures of individual component services and of the network can undermine the dependability of the entire application relying on service composition.

Our research is intended to contribute to achieving higher dependability of Web Service composition. We have developed a novel solution, called WS-Mediator system, implementing resilience-explicit computing and fault tolerance mechanisms to improve the dependability of Web Service composition. It consists of a number of subsystems, called Sub-Mediators, which are deployed at various geographical locations across the Internet to monitor Web Services and dynamically generate Web Service dependability metadata in order to make resilience-explicit decisions. In addition to applying the fault tolerance mechanisms that deal with various kinds of faults during the service composition, the resilience-explicit reconfiguration mechanism dynamically selects the most dependable Web Services to achieve higher service composition dependability fault tolerance.

A specific instance of the WS-Mediator architecture has been developed in the Java Web Service technology. A series of experiments with real-world Web Services, in particular in the bioinformatics domain, have been carried out using the Java WS-Mediator. The results of the experiments have demonstrated the applicability of the WS-Mediator approach.