A Graphical Petri Nets Simulator - Rochester Institute of Technology

The arcs that connect the input places and the transitions are called inhibitor
arcs.
1.3.1 State Machines
State machines are basic Petri Nets that are restricted so that each
transition has only one input and one output. These nets are obviously
conservative and finite-state. They have very high decision power, but are of
limited usefulness in modeling systems that are not finite[5][7].
1.3.2 Marked Graphs
Differing from state machines, marked graphs restrict the places, but
not the transitions, to only one input and one output. It can be said that
marked graphs are the dual of state machines. This rule eliminates sharing of
places between transitions and so eliminates conflict. There are known
algorithms that show that a marked graph is live and safe,
reachability problem for marked graphs. Thus,
and solve the
marked graphs have high
decision power, but have limited modeling power[5][7]. Since marked graphs
have no branch control flow, parallel activities can be easily modeled, but not
alternative activities.
1.3.3 Free Choice Nets
In free choice nets each arc from a place is either the unique output of
the place or the unique input of a transition. This restriction means that if
there is a token in a place then either the token will remain in that place until
its unique output transition fires or, ifthere are multiple outputs for the place,
then there is a free choice as to which of the transitions is fired. The liveness
and safeness for free choice Petri Nets are decidable and have necessary and
sufficient conditions for these properties[5].
Those nets described above are generally called Condition/Events nets
(C/E nets). A C/E net has the following
special characterstics.
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