A specialized class "is" a specialization of another class and, therefore,
has the ISA relationship with the other class. An Employee ISA Person. This relationship
is best implemented with inheritance. Employee is derived from Person. A class may
have an instance of another class. For example, an employee "has" a salary,
therefore the Employee class has the HASA relationship with the Salary class. This
relationship is best implemented by embedding an object of the Salary class in the
Employee class.