Design and Implementation of a Distributed Workflow Enactment Service

Workflows are activities involving the coordinated execution of multiple tasks performed by different processing entities, mostly in distributed heterogeneous environments which are very common in enterprises of even moderate complexity. In current commercial workflow systems, the workflow scheduler is a single centralized component. A distributed workflow enactment service on the other hand should contain several schedulers on different nodes of a network each executing parts of process instances. Such an architecture would fit naturally to the distributed heterogeneous environments. Further advantages of distributed enactment service are failure resiliency and increased performance since a centralized scheduler is a potential bottleneck. In this paper we present the design and implementation of a distributed workflow enactment service based on the work given in [12]. Yet by starting with a block structured workflow specification language we avoid the very general set of dependencies and their related problems. In this way it is possible to present a simple algorithm for distributed scheduling of process instances. Further benefits of the approach are the ease in testing and debugging the system and execution efficiency through reduced number of messages.