There is a parking facility, where each level can be represented by an 8x20 rectangular grid of car slots. There are two entrances and two exits located at opposite sides of the car-park. When a car enters, its registration is recorded and a specific car slot is allocated. This allocation is determined automatically in random, for the level the customer prefers. Charges are calculated according to the hours of stay and paid at the exit desk.

The system should allow the following users to operate it:

o An entrance desk operator to record the information of either a registered regular customer or a casual customer (via the car plate number). Also, the allocation of a car slot should be provided by this subsystem.

o An exit desk operator who can free a previously allocated car slot, charge the leaving customer accordingly and record exit times.