er modeling practice exercise solutions mba 8473
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ER Modeling Practice Exercise Solutions
MBA 8473
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PROBLEM 1. (This is just one way of doing this problem. Other versions are possible depending on what assumptions you make).
ASSUMPTIONS:
(It will be beneficial to think about what a ‘car’ means in this situation. Is it a car? Or, is it a sold-car? Etc.)1. VIN# provides unique identification2. Year of make can be found from VIN#3. PRE-OWNED is a yes/no attribute
1. MODEL-TYPE is unique2. We are going to capture only the latest
recall info3. Etc. etc.
ENTITIES:
CARVIN#ARRIVAL-
DATEDEALER-PRICEPRE-OWNEDSELL-TIME-
STAMP...MODEL
MODEL-TYPESTART-DATELAST RECALL...
1. We do not want to use ss# as unique identifier2. To be a customer in the database the person
should have bought at least one car.Etc etc.
CUSTOMERCUSTOMER-ID-NUMBERCUST1-F-NAMECUST1-L-NAME…
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PROBLEM 1 continued:
ER Model
bought
MODEL
Has aRelationship related assumptions:1. One customer can buy many cars over time2. A car can be bought by one customer only3. To be a customer one has to buy a car4. A car can have only one model5. Etc. Etc.
CUSTOMER SOLD-CAR0Is bought by
Can belong to
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PROBLEM 2.Note that the ERD solution for problem 1 can meet most of the requirements of problem 2 except the fact that we do not need model info for problem 2.Only kink in this problem was the use of USED-CARS and NEW-CARS. In this particular case it is convenient to capture that as an attribute called PRE-OWNED (yes/no) like I already did for problem 1.Another way to treat this in the ERD will be to recognize two sub-type entities viz., USED-CARAnd NEW-CAR for a super entity called CAR. Can be done like this:
CAR
USED-CAR NEW-CAR
Is a
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PROBLEM 3. (This is just one way of doing this problem. Other versions are possible depending onwhat assumptions you make). Partial solution only.
ENTITIES:
CUSTOMER
SOFTWARE
SOFTWARE-TYPE
BETA-STAGE (all beta-stage types may not be used at a given point of time)
SALES-AGENT
PROMOTION
(PROMOTION-TYPE+DATE is unique identifier)
Hints for the relationships:
Customer and Software – zero/many to zero/many
Software-type and Beta-stage – one to one (assumption: a given software type can only be in a one beta)
Customer and Sales-agent – (many to one) See P&G example from class notes.
Promotions (are sent to ) Customers – Many to many.
You should be able to fill the rest from this!
SOFTWARE and SOFTWARETYPE – one/one to one/one
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PROBLEM 3 continued:
ER Model
Can buyCUSTOMER SOFTWARE0 SOFTWARE-TYPE
PROMOTIONSSALES-AGENT BETA-STAGE
0Was a
Receives Can be in a
0
0
Is assigned to