Petri net

noun7

1. •
   One of several mathematical representations of discrete distributed systems, a 5-tuple (S,T,F,M_0,W)!, where
2. •
   S is a set of places.
3. •
   T is a set of transitions.
4. •
   S and T are disjoint, i.e. no object can be both a place and a transition
5. •
   F is a set of arcs known as a flow relation. The set F is subject to the constraint that no arc may connect two places or two transitions, or more formally: F⊆(S×T)∪(T×S).
6. •
   M_0:S→ℕ is an initial marking, where for each place s∈S, there are n_s∈ℕ tokens.
7. •
   W:F→ℕ⁺ is a set of arc weights, which assigns to each arc f∈F some n∈ℕ⁺ denoting how many tokens are consumed from a place by a transition, or alternatively, how many tokens are produced by a transition and put into each place.