We use an industrial plant metaphor with tanks and pipes. Tanks Tank1, Tank2 and Tank3 represent the states state1, state2 and state3.
Tanks change color intensity when a state is enabled. .
This world wass created by Ryan M. Donahue, a student in CAP 5805. Clicking the left mouse button over the model signifies an input. The water emptying from one tank to another illustrates which transition is activated by the input. When viewing the world, click anywhere over the model to activate the animation. I started with the model in Dr. Fishwick's website.