Question
Hello, I'm having trouble understanding entities in database. How do I find out which is the...
Hello,
I'm having trouble understanding entities in database. How do I find out which is the super key, candidate key, and primary key? I dont undersntad
Thank you for your help in advance
3) Consider the following entities representing persons (owners and drivers), vehicles, ad accidents: person (ssn, name, street, city, state vehicle (vin Num, make, model, year) owner (ssnOwner, vinNum, date accident (accidentNum, ssnOwner, ssnDriver, vinum, accidentloc, date) accidentNum is for an accident incident which is the sam accident. e number even if three or more vehicles are involved in an α) Write down the superkeysforaccidSnr:Nam)メ ^ccoule Cankwecen acciden o(Cレイ accident b) Write down the candidate keys for woks: Sufer Keys c) Suggest a primary key for wopks:
Answers
superkey -- superkey is a combination of attributes that can be uniquely used to identify a database record. A table might have many superkeys.
AccidentNum , VinNum ,ssnDriver,accidentLoc,Date are a combination of attributes that uniquely identify a record. While ssnOwner is not uniquely identified as a record.Because ssnOwner has multiple vehicles.
Candidate keys--Candidate keys are a special subset of superkeys that do not have any extraneous information in them.
AccidentNum , VinNum are a subset of the super key which identified the record uniquely.
Primary Key-- The attribute or combination of attributes that uniquely identifies a row or record in a relation is known as a primary key.
VinNum is primary key that uniquely identifies a row or record in a relation.
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