A relationship type can be classified by the number of entity types involved, and by the degree of the relationship type, as is shown in Fig. 3.6. These methods of classifying relationship types are complementary. To describe a relationship type adequately, you need to say what the name of the relationship type and its inverse are and their meaning, if not clear from their names and you also need to declare the entity type or types involved and the degree of the relationship type that links the entities. We now discuss the latter two items.