As we introduce many different objects, we use two kinds of relationships to connect. These are the subclass-superclass relationship (a.k.a. specialization or inheritance, "man is an animal", etc.) and the type-instance relationship (a.k.a instantiation, "Joe is a man", etc.). If you are familiar with these concepts, all is well and you can proceed, otherwise you might want to take a detour through the section called “Object-Oriented Relationships”.