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). 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.MODEL-TYPE is unique 2.We are going to capture only the latest recall info 3.Etc. etc. ENTITIES: CAR VIN# ARRIVAL-DATE DEALER-PRICE PRE-OWNED SELL-TIME-STAMP... MODEL MODEL-TYPE START-DATE LAST RECALL... 1.We do not want to use ss# as unique identifier 2.To be a customer in the database the person should have bought at least one car. Etc etc. CUSTOMER CUSTOMER-ID-NUMBER CUST1-F-NAME CUST1-L-NAME …

PROBLEM 1 continued: ER Model bought MODEL Has a 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. CUSTOMERSOLD-CAR 0 Is bought by Can belong to

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 USED-CARNEW-CAR Is a

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 SOFTWARE 0 SOFTWARE-TYPE PROMOTIONS SALES-AGENT BETA-STAGE 0 Was a Receives Can be in a 0 0 Is assigned to