Inheritance vs. embedding

• Consider example of a salary object:
  

  class Salary {
  Salary();
  $\tilde{\;}$ Salary();
  void raise(double newSalary);
  ...
  };

• Might think of deriving Employee from Salary so that we can say theEmployee.raise(); to raise the employee's salary
• Technically, nothing wrong
• Architecturally, very bad decision!
• Rule of thumb: derive B from A only if B can be considered as an A
• In this case, better embed a Salary object as a data field of the Employee class