On Generating Hierarchical Workflow Nets and their Extensions and Verifying Hierarchicality

摘要

For designing and analyzing complex workflow nets the notion of hierarchical decomposition can be essential for keeping the structure of the workflow comprehensible. In this paper we study two classes of nets: hierarchical nets and extended hierarchical nets. The first have a simple hierarchical structure and can be defined in terms of five simple refinement rules. We show that for arbitrary nets it can be easily verified if they can be constructed this way, thus confirming their good design and the properties following from it. As we prove, this can be done by performing the refinements in reverse, i.e., by contracting subnets into single nodes. It is shown that the choice of the contracted subnet does not change the final result of the process, and therefore this procedure for checking the hierarchical structure requires no back-tracking. The second class, extended hierarchical nets, is an extension of the first class where two types of extra refinements are introduced that allow to indicate (1) the synchronization between two parallel running subworkflows or (2) the transfer of a thread from one subworkflow to another one.