Hierarchical graph models of concurrent CIM systems

A concurrent computer-integrated manufacturing (CIM) system modeling technique, called hierarchical graph (HG) modeling, is presented, along with its language extension, called parallel flow graph (PFG). HG is an abstract parallel machine, that is, a model of concurrent computation, that can be used to describe the logical structure of a CIM system and the relationships among each subsystem and the global control system. In particular, HG is capable of defining each subsystem and composing them hierarchically to realized a complex CIM system. The HG formalism is based on a three-part division of computation along logical boundaries: a data model based on hierarchical graphs, a static program model of basic instruction blocks, and a control-flow model based on timed Petri nets. Using an analysis of the reachability set of the timed Petri net, it is possible to determine the possibility of system deadlock, automatically locate and prevent improper concurrent accesses to shared data, and develop minimum and maximum time bounds for processes in the CIM system