ER Modeling Practice Exercise Solutions
MBA 8473
PROBLEM 1. (This is just one way of doing this problem. Other versions are possible depending
on what assumptions you make).
ENTITIES:
CAR
VIN#
ARRIVAL-DATE
DEALER-PRICE
PRE-OWNED
SELL-TIME-STAMP
...
MODEL
MODEL-TYPE
START-DATE
LAST RECALL
...
CUSTOMER
CUSTOMER-ID-NUMBER
CUST1-F-NAME
CUST1-L-NAME
…
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 identification
2.
Year of make can be found from VIN#
3.
PRE-OWNED is a yes/no attribute
1.
2.
3.
1.
2.
MODEL-TYPE is unique
We are going to capture only the latest
recall info
Etc. etc.
We do not want to use ss# as unique identifier
To be a customer in the database the person
should have bought at least one car.
Etc etc.
PROBLEM 1 continued:
ER Model
bought
CUSTOMER
0
Is bought by
Relationship related assumptions:
1.
One customer can buy many cars over time
2.
A car can be bought by one customer only
3.
To be a customer one has to buy a car
4.
A car can have only one model
5.
Etc. Etc.
SOLD-CAR
Can belong
to
Has a
MODEL
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-CAR
And NEW-CAR for a super entity called CAR. Can be done like this:
CAR
Is a
USED-CAR
NEW-CAR
PROBLEM 3. (This is just one way of doing this problem. Other versions are possible depending on
what 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
PROBLEM 3 continued:
ER Model
Can buy
CUSTOMER
Is assigned to
SALES-AGENT
0
0
SOFTWARE
Receives
Was a
SOFTWARE-TYPE
Can be
in a
PROMOTIONS
BETA-STAGE