In Figure 2-3 each box represents a distinct class. The text element in the top half of each box is the class name.
Lines connecting boxes indicate associations.
The class that is connected directly to the diamond 'contains' zero to n instances of the class at the opposite end of the connector. An open circle at the end of the connector denotes 'zero or one'. A closed circle indicates 'zero or more'. No symbol at the end of the connector indicates exactly 'one'. An 'i' immediately after the diamond indicates an inherited attribute.