11. PGT Computer Science Question Discussion

A relation database which is in 3NF may still have undesirable data redundancy because there may exist.

1. Transitive functional dependencies
2. Non-trivial functional dependencies involving prime attributes on the right-side.
3. Non-trivial functional dependencies involving prime attributes only on the left-side.
4. Non-trivial functional dependencies involving only prime attributes.

Option (1) tells transitive functional dependencies so it is not in 3NF so it is wrong

 

Option (2) tells prime attributes on the right side it means there is no non prime attribute in right side so it should be in 3NF because 3 NF me NP->NP nahi hona chahiye and for 2NF P->NP bhi nahi so right side me agar NP attributes hai to problem hai bcoz use case left side me only key honi chahiye means right side me agar Prime attributes hai to left me kuch bhi koi problem nahi hai, but it may or may not be in BCNF. So it may contain  undesirable data redundancy

Option (3) prime attributes in left side means if Prime -> NP then it is no in 2NF so not in 3NF

option (4) involving only prime attributes means it is in BCNF so no data redundancy 

So Option "2" is correct