Inheritance implies the existence of some property
of a class of objects and the ability of this property to
be had (or inherited) by subclasses of objects (topdown),
or superclasses of objects (bottom-up).
Cancellation of inheritance occurs when exceptional
subclasses exist that do not possess a property of the
class they are derived from. When the inheritance
hierarchy takes the form of a tree, it is called treestructured
inheritance.