When Inheritance Is Not a Good Idea

Inheritance in a data model is not as common as you might think at first. Humans are very good at categorizing things into hierarchies, and once people get hold of the idea of inheritance in data modeling, there can be a temptation to use it everywhere. In the last section, I was careful to say that an affirmative answer to the question "Is A a type of B?" only meant that using inheritance might be a possible way of making sense of a problem. In this section, we will look at a couple of examples where inheritance is definitely not a good way to think about a problem.

Confusing Objects with Subclasses

Consider a database of dogs of different breeds. We may have a hierarchy of breeds and might at first sight think that inheritance is a possibility. Consider the following statements: