Simulation, like a gem, is multi-faceted. Several subfields of simulation have emerged based on the characteristics of models used in a simulation study, on the nature and the generation characteristics of model behavior, also on the agent soch as a computer which generates model behavior. For example, one distinguishes: - deterministic simulation, stochastic simulation, stiff simulation based on functional rela- tionships of descriptive vuriables of models used; - combined simulation, continuous simulation, discrete simulation, process simulation, dis- crete event simulation,...