Daios : Ef ! cient Dynamic Web Service Invocation

72 Published by the IEEE Computer Society 1089-7801/09/$25.00 © 2009 IEEE IEEE INTERNET COMPUTING S oftware systems built on top of serviceoriented architectures (SOAs)1 use a triangle of three operations — publish, !nd, and bind — to decouple roles participating in the system. Publish and !nd put requirements on the service registry and the interface de!nition language. To publish services, an expressive and extensible service de!nition language must be available and supported by the service registry.2 The bind operation, however, is independent from the service registry and is handled by the service consumer. In a SOA, consumers must be able to connect to any service they discover during the !nd step. In addition, they must be able to change this binding at any time (speci!cally, at runtime) if the original target service becomes unavailable or if the !nd operation discovers services delivering a more appropriate quality of service level. Currently, application developers generate stubs (service access components, which are typically compiled from a formal service description such as the Web Services Description Language [WSDL]) to invoke services. These stubs handle the actual invocation but are speci!c to a service provider. If the application invokes a similar service from a different provider, it must regenerate the stubs because services from different providers in the real world never look quite the same. Even if the services provide similar functionality, they usually differ Systems based on the service-oriented architecture (SOA) paradigm must be