A model-driven method for describing and predicting the reliability of composite services

Service-oriented computing is the prominent paradigm for viewing business processes as composed of functions provided by modular and standardized services. Web services are the building blocks for the application of service-oriented computing on the Web and provide the necessary support for the consolidation of multiple services into a single composite service corresponding to the overall process. In such a context, service providers are strategically interested in both describing the quality of service (QoS) characteristics of offered services, to better qualify their offer and gain a significant advantage in the global marketplace, and predicting the level of QoS that can be offered to service consumers when building composite web services that make use of services managed by various service providers. This paper illustrates a model-driven method to automatically describe and predict the QoS of composite web services specified by use of business process execution language (BPEL). The paper specifically addresses the reliability characteristic of the QoS. The proposed method is founded on Q-WSDL, a lightweight WSDL extension for the description of the QoS characteristics of a web service, and exploits Q-WSDL to annotate reliability data onto a BPEL-based UML model of the composite service. The UML model is then used to predict and describe the reliability of the composite web service. The proposed method is illustrated by use of an example application that deals with a composite web service for the migration of PSTN telephone numbers.