Programming by Difference

1. OOP
1. Add new behavior (add new method to derived class)
2. Replace behavior (override base class method)
3. Re-use behavior (do nothing, defaulting to inherited behavior)
4. Only changes in behavior require changes in program code
5. is_a relationship
2. HSM
1. Add new behavior (add new event handler to substate)
2. Replace behavior (re-define superstate event handler)
3. Re-use behavior (do nothing, defaulting to superstate event handler)
4. Only changes in behavior require changes in program code
5. is_in relationship