# Discrete Event System Specification (DEVS) DEVS is a formal, modular framework for specifying discrete-event simulation models, developed by Bernard Zeigler in the 1970s. It defines two building blocks: an **atomic model**, which has its own state, internal and external transition functions, an output function, and a time-advance function; and a **coupled model**, which wires atomic models together into hierarchies through explicit port connections. DEVS underpins much of modern [[Discrete-Event Simulation (DES)]] theory. It is expressive enough to encode most other discrete-event formalisms, and its modular structure makes models composable and closed under coupling, meaning that any valid coupling of DEVS models is itself a DEVS model. Extensions such as Hybrid DEVS allow continuous dynamics to be combined with discrete events, bridging to [[System Dynamics]]-style modelling. # References - [The Discrete EVent System specification (DEVS) formalism](https://www.cs.mcgill.ca/~hv/classes/MS/DEVS.pdf) — Zeigler's canonical description - [The DEVS Framework for Discrete Event Systems Control](https://scispace.com/pdf/the-devs-framework-for-discrete-event-systems-control-57mwlapuin.pdf) - [DEVS Quantization (University of Arizona)](https://www.cs.mcgill.ca/~hv/articles/Quantization/UnivArizonaCDRL2.pdf)