1 Introduction

1.5 The Petri Net Graph

We had the specification:

 Activities   pre-condition      post-condition
 READ COIN    READY              COIN READ, not READY
 DISPENSE     COIN READ, GS      READY, GF
 REFILL       GF = 5             GS = 5, GF empty

Modeling the activities we obtain the following graph:

                  READ
                ________
            R   |      |     CR
    READY (•)-->| READ |--->( ) COIN READ
            ^   | COIN |     /
             \  --------   /
              \            /   
               \          /
                \  DISP  /
                _\ _____v__
                |         |     
      GF ( )<---| DISPENSE|<---(5) GS
          \     |         |    ^
           \    -----------   /
            \                /
             \              /
            5 \            /  5 
               \          /
                \  REF   /
                _v _____/__
                |         |     
                | REFILL  |
                |         |
                -----------

We have also introduced some additional abbreviations for the transitions and for the place READY (R) and COIN READ (CR). The initial state is that the machine is ready with five dispensable items.

We now show how the corresponding Petri Net structure looks like.