Components of a System

• An entity is an object of interest in the system. E.g. customers in a bank.
• An attribute is a property of an entity. E.g. the checking account balance of the customer.
• An activity represents a time period of specified length. Here the time period is emphasized because often the simulation involves time. E.g. deposit money into the checking account at a specified date and time.
• The state of a system is defined to be that collection of variables necessary to describe the system at any time, relative to the objectives of the study. E.g. number of busy tellers, number of customers waiting in line.
• An event is defined as an instantaneous occurrence that may change the state of the system. E.g. customer arrival, addition of a new teller, customer departure.