An Introduction to Discrete-Event Modeling and Simulation with Devs

The Discrete-Event System Specification (DEVS) is a popular formalism devised by Bernard Zeigler in the late 1970s for modeling complex dynamical systems using a discrete-event abstraction. At this abstraction level, a timed sequence of pertinent "events" input to a system (or internal timeouts) causes instantaneous changes to the state of the system. The main advantages of DEVS are its precise, implementation independent specification, and its support for modular, hierarchical composition. This tutorial introduces the Classic DEVS formalism in a bottom-up fashion, using a simple traffic light example. The syntax and operational semantics of Atomic (i.e., non-hierarchical) and of Coupled (i.e., hierarchical, connecting interacting components) models are introduced. Finally, a simplified DEVS model for performance analysis of vessel movements in the Port of Antwerp is presented. All examples in the paper use PythonPDEVS, though other DEVS tools could equally well be used. We conclude with suggestions for further reading on DEVS theory, variants, and tools.