1. A bike sharing application on mobile phone is used to rent bikes to users. Users need to open the App first, register an Account in the App by inputing usernames and passwords, find a bike nearby and scan the QR code. Then, the App contact the server to request the renting of the bike. Next, if the server allow the renting behaviour, the command of unlocking the bike is sent to the bike and the lock of the bike is unlock. Finally, the user is able to ride the bike. The using of the bike is charged 1.5 yuan per half hour. When the bike is locked by the user, the renting is finished and user need to pay for the order. Users can also buy some cards to save money. For example, Week-cards let users ride bikes for free in the period of one week, and Month-card let users use bikes for free in one month. Each card has a start time and a deadline and each card only belongs to one Account. There are two types of bikes. One type is the traditional bike (H-bike) and another type is the electric bike (E-bike). There are GPS on bikes sending physical positions to servers every minue. Each order has riding, unpaid and finished status.

(3) The App need to communicate with a remote server to rent bikes and pay for the order. Therefore, some boundaries classes are required for changing information with servers. Controllers are also needed to control the status of orders. Build an application class diagram for the system by adding boundary, user interface and controller classes.

(4) Build an activity diagram to describe the process of renting and return bikes. Tips for the process: When the user scan the QR code, if the bike is unavialable, the request to renting this bike is refused. When the bike is locked, the App needs to find wheather there are Week-cards or Month-cards. If there are Week-cards or Month-cards, the start time and the deadline are checked. If the card is not expired, the user need not to pay for the order. Otherwise, the user need to pay for the order.