As described earlier, a super class and its sub classes and their sub classes, and so on, is
called a type hierarchy. An example of a type hierarchy is shown in Figure 12.4, where the
job roles specialization/generalization shown in Figure 12.2 are expanded to show a shared
subclass called Sales Manager and the subclass called Secretary with its own subclass called
Assistant Secretary. In other words, a member of the Sales Manager shared subclass must be
a member of the Sales Personnel and Manager sub classes as well as the Staff super class. As
a consequence, the attributes of the Staff super class (staff No, name, position, and salary), and
the attributes of the sub classes Sales Personnel (sales Area and car Allowance) and Manager
(mgrStartDate and bonus) are inherited by the Sales Manager subclass, which also has its own
additional attribute called sales Target.