          +-------------+                    +-------------+
          |   Vehicle   |                    | <<iface>>   |
          +-------------+                    |  Drivable   |
                /_\                          +-------------+
                 |                                 /_\
        +--------+--------+                         :
        |                 |                         :
  +-----------+     +-----------+             +-----------+
  |    Car    |     |   Truck   |             |  Driver   |
  +-----------+     +-----------+             +-----------+
       <>                 *
       |                  |
  +-----------+     +-----------+
  |   Wheel   |     |   Cargo   |
  +-----------+     +-----------+
