Web services are proposed as a way to enable loosely-coupled integration of business processes of different stakeholders. This requires effective development mechanisms that focus on modeling of business logic rather than on low-level technical details. This problem has been recognized by several researchers, and they have mainly proposed the use of process-oriented languages (e.g., UML Activity Diagrams). However, process-oriented approaches limit the definitions of Web services only to the context of concrete business processes (where the services are used). To overcome this limitation, in this paper, we propose a modeling approach that enables one to model Web services from the perspective of the underlying business logic regulating how Web services are used regardless of the context where they are used. This is done by modeling Web services in terms of message-exchange patterns, where each service is described by a (set of) rule(s) regulating how Web services' messages are exchanged. By leveraging the principles of model-driven engineering, we define a rule-based modeling language supporting the proposed modeling approach. More specifically, the rule-based modeling language supports reaction rules (also known as Event-Condition-Action rules) to model Web services in terms of message exchange patterns. Our approach is supported by an extension of the well-known UML tool Fujaba and by a number of model transformations for round-trip engineering between Web services and reaction rules.
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