It is completely normal to have a hierarchy of data buried within the taxonomy. In Figure 8.8 it is seen that there is a hierarchy of cars. The hierarchy has a first level of sports car, hybrid car, utility car, and SUV. Then, within the first level of categorization, there is another level of categorization – a sports car may be a Porsche or a Ferrari.
Figure 8.8 Hierarchies within a taxonomy
Indeed, this creation of a hierarchy within a taxonomy can (and usually does) go much further than the two levels of hierarchy that are shown in Figure 8.8.
There is an important implication when considering the levels of ...