Use UML class diagram to model the elevator system of a multi- floors building. The elevator system is composed of 20 floors and n elevators. Each elevator has two doors and a keypad consisting of a set of buttons, one for each floor. The buttons light up when they are pressed. This, in turn, cause the elevator to visit the corresponding floor. The light goes out upon the elevator’s reaching the floor. Each floor (except for the ground and top floors) has two buttons, one for request an up-elevator and one to request a down-elevator. The illumination goes out when the elevator visits the floor and either is moving in the desired direction or has no outstanding requests. Each elevator equipped with an emergency button that, when is pressed, causes a warning signal to be sent to the site manager. The elevator is then deemed “out of service.” Each elevator has a mechanism to cancel its out-of-service status.

a. Model this system in an object-oriented design using UML class diagram

b. Suppose that the elevators are divided into two sets: the first set comprising the elevators that serve floors zero through floor 9, the second set comprising those which serve floors 10 through 19. Revise your initial design to incorporate this new feature.