What Is 3nf?


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Ambika ambi Profile
Ambika ambi answered
The third normal form says that a primary key should uniquely identify all other non prime key. There should not exit transparent dependency.

For example take a relation of employee - name,eno,dob,address,dno,dname,mgreno as its attributes.

Here eno is primary key which uniquely identifies name,dob,address,dno and dno which is non prime attribute identifies dname,mgreno.eno identifies dname and dloc via dno. This means dname and dloc traperantly depend on eno.

To bring this relation to 3nf we have to separate these relation into two,as emp which has name,eno,dob,address,dno as its attributes here dno is foreign key.

Another relation is dept which has dnum,dname and mgreno as its attributes.Here dnum is primary key it is refered by dno from the relation emp.

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