效绵 Informal Definition ■ The graphical presentation of a Petri net is a bipartite graph There are two kinds of nodes o Places:usually model resources or partial state of the system o Transitions:model state transition and synchronization Arcs are directed and always connect nodes of different types Tokens are resources in the placesInformal Definition ◼ The graphical presentation of a Petri net is a bipartite graph ◼ There are two kinds of nodes  Places: usually model resources or partial state of the system  Transitions: model state transition and synchronization ◼ Arcs are directed and always connect nodes of different types ◼ Tokens are resources in the places