14.1 Explain why adopting an approach to design that is based on loosely coupled objects that hide information about their representation schould lead to design that may be readily modified.

Ans. “Changing the internal details of an object is unlikely to affect any other system objects”. If the objects are loosely coupled “it is usually straightforward to introduce new objects without significant effects on the rest of the system”. These reasons lead to a design that may be readily modified.

14.4 Using the UML graphical notation for object classes, design the following object classes identifying attributes and operations. Use your own experience to decide on the attributes and operations that schould be associated with the objects: A telephone, A printer for a personal computer, a personal stereo system, A bank account, Alibrary catalogue.

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14.7 Do Sequence diagram for peterol station only.

♦ A petrol (gas) station is to be set up for fully automated operation. Drivers swipe their credit card through a reader connected to the pump; the card is verified by communication with a credit company computer; and a fuel limit is estiablished. The driver may then take the fuel requried. When fuel delivery is complete and the pump hose is returned to its holster, the driver’s credit account is debited with the cost of thr fuel taken. the credit card is returned after debiting. If the card is invalid, the pump returns it before fule is dispensed.

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