As an example of the sort of complexity that can arise when dealing with a real-world taxonomy, consider that with multiple levels of hierarchy in a taxonomy, it is possible to have different types in the taxonomy. For example, the taxonomy for “Car” may have cars “typed” by car type: sports, utility, and so forth. But it is also possible to have cars categorized by cost: expensive, less expensive cars. Or it is possible to have cars “typed” by weight. In fact, cars may be categorized many different ways. And of course, the same car can be found in many different categories.