CUSTOMER
1.
get valid
customer
selection
2
.
look-up
product
price
3.
get
payment
4.
dispense
product
5.
dispense
change
PRODUCT
 TABLE
CUSTOMER
CUSTOMER
selection
valid
    selection
returned
   change
product and price
object
product
selected
product
returned
object
PRICE TABLE
PRODUCT
 TABLE
product
     requested
T
T
T
T
product
dispensed
no
product
product
OK
coin return
requested
coins
OK
0.
vend
control
program
change
dispensed