A node class is a class that,

► relies on the base class for services and implementation,

► provides a wider interface to the users than its base class,

► relies primarily on virtual functions in its public interface

► depends on all its direct and indirect base class

► can be understood only in the context of the base class

► can be used as base for further derivation

► can be used to create objects.

A node class is a class that has added new services or functionality beyond the services inherited from its base class.