Supporting Ad-hoc Changes in Distributed Workflow Management Systems.

Flexible support of distributed business processes is a characteristic challenge for any workflow management system (WfMS). Scalability at the presence of high loads as well as the capability to dynamically adapt running process instances are essential requirements. Should the latter one be not met, the WfMS will not have the necessary flexibility to cover the wide range of process-oriented applications deployed in many organizations. Scalability and flexibility have, for the most part, been treated separately in literature thus far. Even though they are basic needs for a WfMS, the requirements related with them are totally different. To achieve satisfactory scalability, on the one hand the system needs to be designed such that a workflow (WF) instance can be controlled by several WF servers that are as independent from each other as possible. Yet dynamic WF changes, on the other hand, necessitate a (logical) central control instance which knows the current and global state of a WF instance. This paper presents methods which allow ad-hoc modifications (e.g., to insert, delete, or shift steps) to be correctly performed in a distributed WfMS; i.e., in a WfMS with partitioned WF execution graphs and distributed WF control. It is especially noteworthy that the system succeeds in realizing the full functionality as given in the central case while, at the same time, achieving favorable behavior with respect to communication costs.