Made Easy Test Series | 3NF | True/False

Question

 

A relation is in 3NF if every non-prime attribute of R is fully functionally reliant on every key of R

1. TRUE
2. FALSE

Answer 1

3NF, or Third Normal Form, is a database normalization rule that states that a relation is in 3NF if every non-prime attribute of R is fully functionally dependent on every key of R.

A non-prime attribute is an attribute that is not part of the primary key of the relation. A functional dependency is an constraint that states that the value of one attribute determines the value of another attribute in the relation. A full functional dependency is a type of functional dependency where the dependency holds for all possible values of the determinant attribute.

In other words, a relation is in 3NF if every non-prime attribute is dependent on the entire primary key and not just a part of it. Additionally, if a non-prime attribute depends on a non-key attribute then it violates 3NF.

A relation is said to be in 3NF if it is already in 2NF and there are no transitive functional dependencies, meaning that if A->B and B->C, then A->C should not exist.

In summary, the 3NF states that every non-prime attribute should be fully functionally dependent on every key of R.

Comments

In other words, a relation is in 3NF if every non-prime attribute is dependent on the entire primary key and not just a part of it.

“Additionally, if a non-prime attribute depends on a non-key attribute then it violates 3NF”. « (This is also imp to mention in the statement), this question does not do that.

The previous one is necessary statement but not sufficient

@Sai Varun Jamalpoor This GATE question (GATE 2012) option “B” also negates this question statement 

Every NPA is dependent on primary key anyway, be it 3NF, or 2NF, as (key → every attribute) always holds, and (NPA ∈ Every attribute)

So, answer to this must be “False” right?

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No

Answer 2

The given key is “TRUE” and explanation as follows::

 

Consider a situation R(A,B,C,D) and FD’s { AB → C, AB → D, C→ D}

Here, key is ‘AB’ and every non-prime attribute of R is fully functionally reliant on every key of R. The FD { C→ D } voilates 3NF conditions as PA {A,B}, NPA{C,D}

So, shouldn’t the answer be FALSE