A Model-driven WSDL Extension for Describing the QoS ofWeb Services

Web services are the building blocks of the emerging computing paradigm based on service-oriented architectures. A Web service is a self-describing, open component that supports rapid composition of distributed applications. Web service definitions are used to describe the service capabilities in terms of the operations of the service and the input and output messages for each operation. Such definitions are expressed in XML by use of the Web Service Definition Language (WSDL). Unfortunately, a WSDL description only addresses the functional aspects of a Web service without containing any useful description of non-functional or quality of service (QoS) characteristics. This paper introduces a lightweight WSDL extension for the description of QoS characteristics of a Web service. The extension is carried out as a metamodel transformation, according to principles and standards recommended by the model driven architecture (MDA). The WSDL metamodel is introduced and then transformed into the Q-WSDL (QoS-enabled WSDL) metamodel. The proposed Q-WSDL extension can effectively be used to specify QoS requirements, to establish service level agreements (SLA), to add QoS-oriented characteristics when querying registries of Web services and to support the automated mapping from WSDL documents to Q-WSDL ones and from UML models to Q-WSDL Web services