Discrete event simulation is used to observe and analyze system behavior. In discrete event simulation, system operation is represented as a predefined sequence of events. Each event occurs at an instance of time and marks related changes to the state of the system. The chronological sequence of events emulates system behavior through a network of interconnected processes that respond when specific inputs (events) change state. These events may be internal or external to the system. The event sequence identifies when these inputs cause the system to change from one state to another. Usually, the input stimulates a cascade of event changes and creates a queue of events to occur at a future time.

INTERLOCKS modeling and simulation tool uses discrete event simulation to depict system operation. The model is built as a network of events (occurrences) within the system. The relationship among the events is described through the use of simple logic and is graphically displayed to the user through the use of AND, OR, and NOT gates. Each gate calculates the system status by using the current state of its requisite events. System behavior is captured at every time element through these logic gate calculations.

Predefined sequences of events called “simulations” emulate complete system operation. These sequences capture the inputs (either internal or external to the system) that when triggered, initiate system reaction. The simulation then uses timing to queue future event occurrences. The input stimuli, the resulting event state changes, and the queue of events to occur at a future time are all captured and displayed to the end user.