ABSTRACT
Once the problem has been properly formulated and the project plan is complete, the simulation practitioner should direct his or her attention toward defining the system that should be modeled. For our purposes, a system is a group of components that receives inputs and delivers outputs. The components determine how the system converts inputs to outputs. The system may exist in an environment that could also potentially affect the inputs and outputs. The system definition and model formulation process consists of determining:
• The system classification • How much of the system to model • What components and events to model • What input data to collect • What output data to generate with the model
Note that we are going to define our system and formulate the model at the same time. In many other simulation texts, these two processes are treated completely independently. By defining our system and formulating the model nearly simultaneously, we are in a better position to understand how the system components will be modeled. In this chapter we focus on what we are going to model. In the following model translation chapter, we discuss the actual process of how we are going to model these components.
One of the first steps that the practitioner must perform in the system definition phase is to classify the system. Systems can be classified with respect to two different dimensions. First, a system may be discrete, continuous, or combined. Second, a system is either terminating or nonterminating. These classifications are a significant issue; they affect how the practitioner will conduct the modeling and analysis for the project (Law and Kelton, 2000).
