Finally it represents the current state of the work in progress, that is, the parts and sub-assemblies that are currently being processed in the case of workshop simulation. Then, running a simulation consists in calculating the state of the system after the next modification, which is assumed to be instantaneous and which is called an event in the discrete events simulation. By calculating the sequence of events, the simulation package computes the evolution of the model during the execution of the simulated process. Their behavior is made realistic by editing the parameters of their properties . The properties are defined in terms of duration, decisions triggering particular events, and flow control.
Simulation is both a new and an old activity of the engineering domain.
It is an old activity because people started simulating about 30 years ago. At that time and until recently, only specialist enginers and researchers were able to understand simulation concepts, and build models by defining them within a simulation language . It is a new activity also, because people concerned by simulation dramatically expand, demanding for software solutions that are more adapted to industrial situations and to engineers more than to researchers. System suppliers are expected to provide price quotations as quickly as possible, in order to decrease their unary cost in a competitive world where the rate of success of these quotations is lower than before. Both of them need numeric simulation results instead of calculating assumptions .