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Consider a relation R(A,B,C,D,E) and the only FDs,

ABD->C

BC->D

CD->E

These are the only 3 FDs. I want to know if the above relation is in 2NF or not.

According to the definition of 2NF, a relation to be in 2NF, it should be in 1NF and it should not have partial dependency.

But I'm not getting the partial dependency concept.

Somewhere it's written that when a proper subset of a key determines a non-prime attribute then it is partial dependency.

Somewhere it's written that when a prime attribute which is not a key determines a non-prime attribute then it is partial dependency.

Because of these 2 different definitions I'm getting confused.

Please help.

user9544852
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1 Answers1

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Second normal form means that each non prime attribute must not depend on a proper subset of a candidate key.

In your example, assuming that the given FDs are a cover of the FDs of the relation, you have two candidate keys, ABC and ABD. Moreover, the attribute E depends on BC, which is a proper subset of the candidate key ABC (you can verify this by computing the closure of BC, BC+, and see that E belongs to that closure).

So the relation is not in 2NF.

Renzo
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