through suitable abstractions and tools is a viable option for improving servicebased computations. T he past few years have witnessed end users' increasing involve ment in the content creation proc ess of modern Web applications (as with Wikipedia) and the emergence of social Web applications (such as YouTube or MySpace). Although these applications benefit from collective usergenerated content, a growing user community is also trying to profit from existing content and services by developing its own Web applications. The phenomenon, commonly known as Web mashups, is driven mostly by skilled users because reusing third party content and services is a non trivial task. This is especially true for Web services, which are based on the notion of programmable interface; for instance, integrating Amazon's search service with currency conversion or shipment services requires pro gramming skills. Service mashups, or userdriven Web service integration approaches, gain momentum by als...