Abstract

DEVS is a popular formalism for modelling complex dynamic systems using a discrete-event abstraction. At this abstraction level, a timed sequence of pertinent “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 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 introduced 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.

Highlights

  • DEVS is a popular formalism for modelling complex dynamic systems using a discrete-event abstraction

  • DEVS [309] is a popular formalism for modelling complex dynamic systems using a discrete-event abstraction

  • We briefly presented the core ideas behind DEVS, a popular formalism for the modelling of complex dynamic systems using a discrete-event abstraction

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Summary

Introduction

DEVS [309] is a popular formalism for modelling complex dynamic systems using a discrete-event abstraction. At this abstraction level, a timed sequence of pertinent “events” input to a system cause instantaneous changes to the state of the system. Compared to DES, DEVS offers modularity which makes it possible to nest models inside of components, generating a hierarchy of models. DEVS is completely formally defined, and there is a reference algorithm (i.e., an abstract simulator) While both DEVS and Statecharts are modular formalisms, Statecharts creates hierarchies through composite states, whereas DEVS uses composite models for this purpose.

Atomic DEVS models
Autonomous Model
Autonomous Model with Output
Interruptable Model
Coupled DEVS Models
Basic Coupling
Input and Output
Tie-breaking
Translation Functions
Closure Under Coupling
The DEVS Abstract Simulator
Application to Queueing Systems
Problem Description
Description in DEVS
Performance Analysis
DEVS Variants
Parallel DEVS
Dynamic Structure DEVS
Cell-DEVS
Other Variants
Summary
Literature and Further Reading
Findings
Self-Assessment

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