An edge from class A to class B in the DAG representing inheritance means that an object of class B is ALSO an object of class A. It has all the properties that objects of class A have, plus additional ones of its own. In particular, it INHERITS all the variables and methods of class A. It can of COURSE provide its own implementations for the inherited methods. And edge from class A to class B in the object containment DAG means that an object of class A contains an object of class B. There need not be any similarities in the properties of A and B. Neither B nor A inherit ANYTHING from the other. They function as independent types, to the extent that an object of class A can access the variables of the B object contained in it only via the B object’s methods.

An edge from class A to class B in the DAG representing inheritance means that an object of class B is also an object of class A. It has all the properties that objects of class A have, plus additional ones of its own. In particular, it inherits all the variables and methods of class A. It can of course provide its own implementations for the inherited methods. And edge from class A to class B in the object containment DAG means that an object of class A contains an object of class B. There need not be any similarities in the properties of A and B. Neither B nor A inherit anything from the other. They function as independent types, to the extent that an object of class A can access the variables of the B object contained in it only via the B object’s methods.