Devs Diagram Revised: a Structured Approach for Devs Modeling

Discrete Event Systems Specification (DEVS) formalism has been used in recent decades for modeling and simulation of discrete event systems as well as for some hybrid systems, since it has a sound semantics for modular hierarchical semantics and good simulation development environments. Nevertheless there are still deep gaps in understanding between the formalism and the practical modeling of large complex systems since the number of events and states of the systems are so huge to handle in the classical DEVS formalism. To solve this problem, this paper proposes the DEVS diagram, a structured diagramic form of the DEVS formalism. For this we introduce the essential notions of state variable and phase for structuring sequential states, and port and message for structuring sequential events. Phase transition diagram is also formally defined. We present the DEVS diagram in both graphical notations and mathematical formulations. A simple example illustrates the modeling method in the DEVS diagram.