Systems simulation with digital computers

By system, we have in mind the meaning accorded by Webster, “a set of objects united by some form of regular interaction or interdependence.” Change in a system is regarded as change in the properties of the objects or in the relationships between the objects. That is, when one considers a physical system or conceives of a hypothetical system, one perceives certain distinct objects such as machines, customers, messages, etc. Each object is seen to possess certain properties of interest that may be used to define it, machine availability, credit status, or length of a message.