Building a modular service oriented workflow engine

Current workflow engines, often based on WS-BPEL, are monolithic programs to orchestrate a business process or take part in choreography between partners. They cover aspects like the execution of the workflow description derived from the business process, the communication with external services, and the handling of errors. Both, the communication with services as well as basic error handling are covered by static and internal APIs [S. Modafferi, E. Mussi, and B. Pernici (2006)], and thus provide only simple strictly internal means of interaction with running workflows. Introducing new repair algorithms or self-healing behavior require detailed monitoring and modification of all aspects of a workflow execution thus requiring a modularization of the workflow engine itself. In this paper we will present a modular and service oriented workflow engine. Modularity and service-orientedness are realized by integrating a workflow execution engine with means of logging, repair and possibility to invoke external services through simple Web-based APIs.