Modeling of hierarchical Petri net-based workflow

In many formalized workflow modeling methods, with mature theory basis and analysis technology Petri Nets can depict and analyse the parallel system well, a model constituted by Petri Nets can be frankly examined and powerful supported by Petri Nets' theory. But in complex applications of the real world, it may run into the state space explosion caused by amounts of nodes. To resolve it, the hierarchical model was proposed, which divide Petri Nets into P and T sets according to some princicles, then abstract the nodes in the same group to a node in the new model, so the nodes reduced. At last, the "philosopher repast problem" showed the advantage of hierarchical model. With its good hierarchical structure, hierarchical model fine the Petri Nets model, so as to achive the purpose of reducing node numbers.