Design for Change: Evolving Workflow Specifications in ULTRAflow

Updating the specification of workflows on the fly in a workflow management system is currently considered an important topic in research as well as application. Yet, most approaches are either very simplistic, allowing only newly started workflows to take advantage of updated specifications, or they are complex, trying to transfer every active workflow from the old to the new schema.In the workflow management system ULTRAflow, updates to workflow specifications are handled by using a multi-version concurrency control protocol. This is facilitated by the specification language for workflows, which is rule based and therefore provides a natural partitioning of specifications into smaller units. The proposed method allows active, running workflows to partly use new specifications if this does not conflict with already executed sub-workflows. Moreover, an architecture which is also applicable in a distributed system is presented.While the method to update the specifications is discussed in the context of a workflow management system, it can also be applied in CORBA or EJB applications, or the now ubiquitous electronic services.