Confirmation: increasing resource availability for transactional workflows

The notion of compensation is widely used in advanced transaction models as means of recovery from a failure. Similar concepts are adopted for providing 'transaction-like' behaviour for long business processes supported by workflows technology. In general, it is not trivial to design compensating tasks for tasks in the context of a workflow. Actually, a task in a workflow process does not have to be compensatable in the sense that the forcibility of 'reverse' operations of the task is not always guaranteed by the application semantics. In addition, the isolation requirement on data resources may make a task difficult to compensate. In this paper, we first look into the requirements that a compensating task has to satisfy. Then we introduce a new concept called confirmation. With the help of confirmation, we are able to modify most non-compensatable tasks so that they become compensatable. This can substantially increase the availability of shared resources and greatly improve backward recovery for workflow applications in case of failures. To effectively incorporate confirmation and compensation into a workflow management environment, a three level bottom-up workflow design method is introduced. The implementation issues of this design are also discussed