Relationships and Cardinalities

Business Case:     Car Rental Inc.
•      The firm has a number of rental agencies in several provinces. Each agency is identified by a Agency_Number and its location.
•      Each agency is assigned one or more employees. Attributes of employee include Employee_ID and Employee_Name. An employee must be assigned to only one rental office.
•      For each agency, there is always one employee assigned to manage that office. An employee may manage only agency to which s/he is assigned.
•      The agencies rent several classes of vehicles: compact, midsize, full size, sport utility. Each vehicle is managed by one agency. Customers might rent vehicles frAom the different agencies.
•      Vehicles are to be described by data such as: make, model, year of production, engine size, fuel type, number of passengers, registration number, purchase price, purchase date, rent price and insurance details.
•      There are two types of customers: privileged and casual. For the privileged category of customers special credit card facilities are provided. These customers may also book in advance (reservation) a particular car. Information stored for each booking (reservation) includes customer, car, estimated amount, date of rental and date on which the vehicle is to be returned. If a vehicle is available, the customer’s details are recorded (if not stored already) and a new booking is made. These reservations can be made for any period of time up to one month.
•      Bookings can be cancelled if the agency is informed at least 24 hrs before the booking date.
•      Casual customers cannot book in advance and must pay a deposit for an estimated time of rental at the time they rent the vehicle, unless they wish to pay by credit card. All major credit cards accepted.
•      For each rental (for either privileged or casual), the agency keeps track of the date it was rented, the date the vehicle is returned, vehicle, customer and the rental total charged amount.
•      Personal details (such as name, address, telephone number, driving license, number) about each customer are kept in the database.
•       A customer (either privileged or casual) cannot rent a car for longer than four weeks. .
•      Vehicles need to be maintained and repaired and the database is required to keep track of this. All major repairs and maintenance are done by subcontractors (i.e. franchised garages), with whom the rental company has long-term agreements. Therefore the data about garages to be kept in the database includes garage names, addresses, range of services and the like. Some garages require payments immediately after a repair has been made; with others the rental company has made arrangements for credit facilities.
1.    Draw the ERD of the database that could be used to support the operations of the business described in the case (6 marks). The ERD should identify:

Primary keys and Foreign keys;
Entities and Attributes;
Relationships and Cardinalities (e.g. one-to-one, one-to-many).

Next to the ERD in your submission, list the assumptions made when designing the ERD. If an element of the business case does not provide the information necessary to know for certain whether one design choice should be made over another, the choice you make will be accepted if it correctly reflects your assumptions.

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