from
The Free On-line Dictionary of Computing (8 July 2008)
Petri net
<parallel, simulation> A {directed}, {bipartite graph} in
which nodes are either "places" (represented by circles) or
"transitions" (represented by rectangles), invented by Carl
Adam Petri. A Petri net is marked by placing "tokens" on
places. When all the places with arcs to a transition (its
input places) have a token, the transition "fires", removing a
token from each input place and adding a token to each place
pointed to by the transition (its output places).
Petri nets are used to model {concurrent} systems,
particularly {network} {protocols}.
Variants on the basic idea include the {coloured Petri Net},
{Time Petri Net}, {Timed Petri Net}, {Stochastic Petri Net},
and {Predicate Transition Net}.
FAQ (http://daimi.aau.dk/PetriNets/faq/answers.htm).
(1996-09-10)