document: Web service interfaces We present a language for specifying web service interfaces . A web service interface puts three kinds of constraints on the users of the service . First , the interface specifies the methods that can be called by a client , together with types of input and output parameters ; these are called signature constraints . Second , the interface may specify propositional constraints on method calls and output values that may occur in a web service conversation ; these are called consistency constraints . Third , the interface may specify temporal constraints on the ordering of method calls ; these are called protocol constraints . The interfaces can be used to check , first , if two or more web services are compatible , and second , if a web service A can be safely substituted for a web service B. The algorithm for compatibility checking verifies that two or more interfaces fulfill each others ' constraints . The algorithm for substitutivity checking verifies that service A demands fewer and fulfills more constraints than service B.
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