Web Service Composition in UML

As the number of available web services is steadily increasing, there is a growing interest for reusing basic web services in new, composite web services. Several organizations have proposed composition languages (BPML, BPMN, BPEL4WS, BPSS, WSCI), but no winner has been declared so far. This paper proposes a method that uses UML Activity models to design web service compositions, and OMG's Model Driven Architecture (MDA) to generate executable specifications in different composition languages. The method utilizes standard UML constructs with a minimal set of extensions for web services. An important step in the method is the transformation of WSDL descriptions into UML. This information is used to complete the composition models. Another key aspect of the method is its independence of the web service composition language. The user can thus select his preferred composition language – and execution engine – for realizing the composite web service. Currently, the method has been implemented to support two executable composition languages BPEL4WS and WorkSCo, with corresponding execution engines. WorkSco is a web service enabled workflow composition language. The method is illustrated with an example from a crisis management scenario.