Web service is an emerging paradigm for distributed computing. First, in order to verify web services rigorously, it is important to provide a formal semantics for the flowbased web service language (WS). A suitable formal model should cover most features of the WS. The existing formal models either abstract from data, cover a simple subset of WS, or omit the interactions between certain components. This paper presents a web service automaton, an extension of Mealy machine, to fulfill the

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... model requirements of the web service domain. Second, semantic compatibility checking between web services is another important issue. The existing checking approaches are post-checking, where the compatibility is checked after composition. As a complement to post-checking, we proposes anti-patterns for web service interactions as a pre-checking, so that certain incompatible web services can be modified or re-selected in the earliest stages.