nBase classes are typically used to establish the common attributes and behavior for an application and to all classes derived from it. .
nA derived class may then
be used to refine and add to the
base class and represent specialized versions, with new or altered data/operations.
nThe relationship between
a derived class and its base class
is often called an "is a" relationship. This is because a derived class "is a" base class.
nA derived class is
everything the base class is and more, because it has been extended or specialized. A derived class object can be used when a base class object is needed.