Abstract

In a Business Process Execution Language (BPEL) process definition the sequence of exchanged messages typically originates from the sequence of business process activities and from the need of coordination of those activities across the participants of the process. As such business concerns (e.g. the sequence of business process steps) are often mixed with technical aspects (e.g. the sequence of coordination messages). In this article we present an architecture to separate business and technical concerns, which results in a clearer overview of the high-level business process and improves the flexibility and maintainability of the orchestration architecture. The described architecture depends on existing Web service standards. Different eventing and coordination specifications are discussed. The ultimate architecture is mainly based on the WS-Brokered Notification and WS-Coordination Framework specifications. 1. Structured Web services orchestration 1.1. A spaghetti of messages Web services orchestration refers to an executable business process that can interact with both internal and external Web services. The interactions occur at the message level. They include business logic and task execution order, and they can span applications and organizations to define a long-lived, transactional, multistep process model [1]. The business process execution language (BPEL) is the leading standard language for orchestration of Web services. A BPEL process defines how multiple service interactions are coordinated to achieve a business goal, as well as the state and the logic necessary for this coordination [2]. Figure 1 shows an example of a business process

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