Title: An Introduction to Classic DEVS,
Abstract: DEVS is a popular formalism for modelling complex dynamic systems using a
discrete-event abstraction. At this abstraction level, a timed sequence
ofpertinent "events" input to a system (or internal, in the case of timeouts)
cause instantaneous changes to the state of the system. Between events, the
state does not change, resulting in a a piecewise constant state trajectory.
Main advantages of DEVS are its rigorous formal definition, and its support for
modular composition.
This chapter 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) models are intruced first. The semantics of
Coupled (hierarchical) models is then given by translation into Atomic DEVS
models. As this formal "flattening" is not efficient, a modular abstract
simulator which operates directly on the coupled model is also presented. This
is the common basis for subsequent efficient implementations. We continue to
actual applications of DEVS modelling and simulation, as seen in performance
analysis for queueing systems. Finally, we present some of the shortcomings in
the Classic DEVS formalism, and show solutions to them in the form of variants
of the original formalism.