Sound Recoveries of Structural Workflows with Synchronization

We consider communication places in workflow nets, where the connected transitions lie in parallel threads. When a workflow Petri net is constructed structurally, by means of refinements, such places cannot be modeled structurally. They are added after the net is constructed. Workflow nets constructed in a structural manner are sound, but addition of such communication places can result in losing the desired soundness property. However, there is a method to avoid such misplacement of communication places. We should limit the pairs of connected transitions to the ones that lie in truly parallel threads and to avoid cycles introduced by communication places. Recovery transitions — special kind of transitions used as a powerful tool in dynamic workflow modeling — allow the manager to move tokens arbitrarily, when some unexpected situation happens. They were extensively studied and proved to be a useful tool in the workflow management [HA00]. They can be modeled as a kind of reset transitions with additional feature of depositing tokens taken from a specified region to particular places in this region, like it was proposed in [Ch06]. Moving tokens arbitrarily by the manager requires a lot of attention, since soundness of the net can easily be destroyed. In this paper we present a sufficient and necessary condition of soundness for a marking in a structured net with communication places. Verifying the condition turns out to be fast. The cost is linear with respect to the total number of places and transitions.