Each box is a bunch of classes.
Classes in 2 mostly inherit from the basic
classes in 1. 3 are just classes for the GUI that make use of business objects.
1 2 3
+---+ +---+ +---+
| | | B | | |
| B | | U | | |
| A | | S | | G |
| S | --> | I | --> | U |
| E | | N | | I |
| | | E | | |
| | | S | | |
| | | S | | |
+---+ +---+ +---+