In Object-Oriented Programming (OOP), everything is modular and hence reusable. More, everything in OOP is an object. Without any loss we also can state: Everything in OOP is a module. But on top of everything in OOP is the class Class. Is this Class a class, an object, a module? It is the ultimate Class, which allows all classes to be classes. Without surprise, the whole OOP system is neatly organized as a hierarchical system with the class Class on top.
Object-orientation is not only a strategy to organize programming, it is applied successfully on nearly all kind of knowledge systems. Hence, knowledge organization, like the Bologna Model, should acknowledge the efforts and results of OOP.