NIELIT 2016 MAR Scientist C - Section C: 3

Question

Every Boyce-Codd Normal Form (BCNF) decomposition is

• A. dependency preserving
• B. not dependency preserving
• C. need be dependency preserving
• D. none of these

Answer 1

BCNF is lossless but dependency preservation isn't guaranteed.

So it may or mayn't be dependency preserving.

A,B,C. Not always true. 

So D is correct. 

Ref: https://www.iitg.ac.in/awekar/teaching/cs344fall11/lecturenotes/september%2006.pdf

Comments

" need be " also means may or may not ( which means if we want we can make it dependency preserving)

Option c indicates that it may be dependency preserving ....there cannot be two options with same meaning right...because according to you A and C have same meaning ...i agree with the fact that dependency preserving is not guaranteed ...so therefore option C could be the right answer.

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As per the screenshot options are not having the word "may".

The word "May" and "Need" are different in meaning and when you read the question along with options, you can see that option C doesn't support the statement "BCNF is lossless but dependency preservation isn't guaranteed.". 

Whereas EVERY BCNF is B) not dependency preserving supports Ǝ BCNF SuchThat they are Dependency preserving.

 

So the ans is option B.

Answer 2

This is a tricky quesion .
The question says that “EVERY BCNF ”
As we know not all BCNF will be dependency preserving
Therefore the answer is option B

Comments

yes answer is option B. The keyword “Every” makes all the difference

Answer 3

UNF--->1NF (Eliminate  multivalue in a cloumn)

1NF-->2NF  Eliminate partial dependency

2NF--> 3NF  Eliminate transitive dependency

3NF-->BCNF  All Determinants must be Candiddate key

Hence BCNF may be Dependency preserving and it is not sure. Hence the option D is correct.

Answer 4

BCNF decomposition is not always dependency preserving hence ans is D