ER Diagrams

Cardinalities on the ER diagram

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3 Replies - 19214 Views - Last Post: 03 May 2009 - 02:46 PM Rate Topic: -----

#1 chetah  Icon User is offline

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ER Diagrams

Posted 17 October 2008 - 07:16 PM

Attached ImageA car rental company has several car rental agencies across the country. The agencies rent several classes of vehicles:compact, midsize, full size, sport utility. Each vehicle is managed by one agency. Customers rent vehicles from the different agencies. When a vehicle is rented, a new rental record is added to the Rental table with dateout as the current date and dateReturned is left null. When a vehicle is returned the record is updated by filling in the DateReturned field. A portion of the car rental table is given below.

Vehicle(VehicleId, VehicleClassId, AgencyId)
Rental( RentalId, VehicleId, CustomerId, DateOut , DateReturned)
Customer( CustomerId, CustomerName, CustomerBalance)
Agency( AgencyId, AgencyLocation)
vehicleClass(VehicleClassId, VehicleClass, RentalRate)


The ER diagram is attached. Am I on the right track? If i am making an ER diagram how do I know that cardinalites are correct?

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#2 jjsaw5  Icon User is offline

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Re: ER Diagrams

Posted 21 October 2008 - 05:19 AM

Please do not double post your questions.
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#3 Mach1Guy  Icon User is offline

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Re: ER Diagrams

Posted 21 October 2008 - 06:41 PM

its looks to me like you are heading in the right direction. when figuring out cardinalities just go from one table to the other and put a verb inbetween the table names along with the cardinality.

for example: an Agency has one to many Vehicles. if it makes sense and is possible, then there you go. if you can think of situations for such cardinality to exist then its correct. theres not really a cut and clean dry way to determine it

This post has been edited by Mach1Guy: 21 October 2008 - 06:43 PM

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#4 speciality  Icon User is offline

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Re: ER Diagrams

Posted 03 May 2009 - 02:46 PM

where did they get that question
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