A Petri net is a graphical and mathematical modeling tool. It consists of places , transitions , and arcs that connect them. Input arcs connect places with transitions, while output arcs start at a transition and end at a place. There are other types of arcs, e.g. inhibitor arcs .
Transitions are active components.
When the transition fires, it removes tokens from its input places and adds some at all of its output places. The interactive firing of transitions in subsequent markings is called token game . As a graphical tool, Petri nets can be used as a visual-communication aid similar to flow charts, block diagrams, and networks. In addition, tokens are used in these nets to simulate the dynamic and concurrent activities of systems. As a mathematical tool, it is possible to set up state equations, algebraic equations, and other mathematical models governing the behavior of systems.