Simulation is the imitation of a physical or conceptual system (process) in order to gain insight into its functioning and to optimize its performance. The act of simulating generally entails representing certain key characteristics or behaviors of a selected physical or abstract system. Key issues in simulation include acquisition of valid source of information about the referent, selection of key characteristics and behaviors, the use of simplifying approximations and assumptions within the simulation, and fidelity and validity of the simulation outcomes.