### Introduction

- Description of discrete system:
- lots of mathematical models, e.g.
- finite state machine
- non-deterministic finite automaton
- generalized semi-Markov process
- PDEVS

- in practice
- in graphical form inside a simulation program

"the thing I've clicked together in my simulation program"
- meaning depends on program interna
- is not explicitly given or even known by modeler
- may change between program versions

- Advantages of mathematical models:
- complete and precise specification
- structural insights by mathematical analysis
- easier to build in a concrete simulation environment
(really!)