Developing High Quality Data Models

17.2. Class and Class of Class

A class is a set whose membership does not change. However, this does not mean that the members we know about do not change. If one class has different membership from another, then they are different. If one class has the same membership as another, then they are the same.

I have shown the classification and specialization relationships in Figure 17-2 as entity types. classification is also shown in Figure 17-1 as the relationship type member__of and specialization is also shown as the relationship type has_superclass in Figure 17-2 . The only difference is that when represented by an entity type, the relationship can itself have attributes and relationships . A classification relationship has a thing as ...