GATE CSE 1998 | Question: 1.34

Question

Which normal form is considered adequate for normal relational database design?

• A. $2NF$
• B. $5NF$
• C. $4NF$
• D. $3NF$

Comments

in the question "adequate normalization method" is asked for real database design ,not " which is best one". i think "adequate means "not more and not less but sufficient"

even though BCNF will have no redundancy while 3NF will have some . but still 3NF is adequate for database design because of following reasons

1) BCNF may cause "loss of dependency"

2) to obtain BCNF , we may require to split relation into smaller one and its number can be huge in large database .which leads to  complex maintenance .

while in 3NF  , even though some redundancies are there but it is better to have some redundancies than having above two problems of BCNF

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3NF removes all the anomalies.

So 3Nf is considered  adequate for relational database dedign.

But then also BCNF is more better than 3NF. But here we are asked adequate one so 3NF is adequate

Answer 1

$3NF$,
because we can always have a $3NF$ decomposition which is dependency preserving and lossless (not possible for any higher forms).

Comments

till 3NF both lossless join and dependency preserving hold .for BCNF lossless join hold but dependency preserving not guaranteed.for higher than BCNF even lossless join also not guaranteed along with dependecy preserving

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why can't it be 2NF, doesn't it follow dependency preservation and lossless join?

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@akshay7797 Higher the normal form, lesser the redundancy. So 3NF is better than 2NF.

Answer 2

Answer: D
3NF will be adequate for normal relational database design since 3NF tables are free of insertion, update, and deletion anomalies.

Comments

Rajarshi Sarkar can you please explain - 3NF tables are free of insertion, update, and deletion anomalies.

Answer 3

3 NF cause it ensures both lossless and dependency preserving ..In BCNF DP is not always possible although it is more strict than 3NF..

Answer 4

Reason of choosing 3NF over BCNF.

               1.We normally choose to retain dependency preservation.

               2.A high penalty in system performance is to be paid or risk the integrity of the data in our database.

Both the reason describe the nature of preference or security and data over the redundancy ,which is satisfy by the 3NF.

Although BCNF satisfy this problem but dependencies are not preserved always.

SO 3NF is correct answer .