ISRO2020-50

Question

If every non-key attribute functionally dependent on the primary key, then the relation will be in

• A. First normal form
• B. Second normal form
• C. Third normal form
• D. Fourth Normal form

Comments

I will claim this question..

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Yes, it is not mentioned whether it is full or partial functional dependency.

The language of question is very poor as it can vary with different interpretations from $1-NF$, $2-NF$, and $3-NF$.

And if I don't presume anything then according to me $\mathbf{1-NF}$ is the only sure shot answer.

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R: {X→Y,  Y→Z,  X→Z}

In above relation,  in FD Y→Z, Z is clearly Non key attribute and It is NOT dependent on Primary key Because Primary key is X.  So, Y→Z is not correct FD for given statement. Answer has to be 3NF.

Answer 1

Option B

https://gateoverflow.in/15778/every-attribute-functionally-dependent-primary-relation

Comments

It should be in 3NF.

Answer 2

Answer - C Third Normal Form.

Why it is not in 2NF:

Let's take simple example:

R: {X→Y,  Y→Z,  X→Z}

In above relation,  in FD Y→Z, Z is clearly Non key attribute and It is NOT dependent on Primary key Because Primary key is X.

Y→Z is not valid functional dependency for the given statement "If every non-key attribute functionally dependent on the primary key". 

We can't take wrong example and prove our answer. 

 3NF Wikipedia definition : "no non-prime attribute depends on other non-prime attributes. All the non-prime attributes must depend only on the candidate keys."  This definition is same as "If every non-key attribute (All the non prime attributes) functionally dependent on the primary key(candidate keys)"

Non prime attribute and Non key attributes are same : http://www.exploredatabase.com/2017/07/define-non-prime-attribute-non-key-attribute-in-dbms.html

 

Comments

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.geeksforgeeks.org/ugc-net-ugc-net-cs-2017-nov-iii-question-9/amp/&ved=2ahUKEwj_uvX9qpTnAhWBILcAHVarCn4QFjABegQIBBAB&usg=AOvVaw0_1xMIkI_JVY9QJMywm726&ampcf=1&cshid=1579597480772

This is ugc net2017 question.

Here every nonkey attribute means that it has to be right side and since only word not mentioned that's why in left side primary or non prime attribute can appear.

So ans is 2nf

Answer 3

Since every non key is dependent on primary key, there is no partial dependency. Therefore definitely  in 2NF.

Since one of the prime attribute may be dependent on a key, this might not be in 3NF.

Therefore 2NF

Answer 4

it is in third normal form. option C.