Functional Dependencies And Normalization (Basic Level)- 1


10 Questions MCQ Test Question Bank for GATE Computer Science Engineering | Functional Dependencies And Normalization (Basic Level)- 1


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QUESTION: 1

Which normal form is considered adequate for relational database design?

Solution:

3NF is considered to be most adequate for relational database design. It always preserves dependency as compare to BCNF which is more io restrictive form of 3NF. Although it does not eliminates redundancy due to MVD’s but it does satisfies two essential properties.
1. If eliminates redundancy due to FD’s. 
2. It preserve FD’s
4NF is not considered to be adequate because it does not preserve FD’s always. 

QUESTION: 2

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

Solution:

Consider, X → A
Since, X is a non key attribute and A is the prime attribute which in turn is consisting of prime attributes the given relation is free from transitive dependency and hence the given relation will be in 3NF.

QUESTION: 3

Given the functional dependencies:
X→W; X→Y; Y→Z and Z→PQ
Which of the following does not hold good?

Solution:


Since there is no FD’s for which W functionally depends on other attributes.

QUESTION: 4

For a database relation R(a, b, c, d) where the domains of a, b, c and d include only atomic values, only the following functional dependencies and those that can be inferred from them hold.
a → c 
b→d
The relation is in

Solution:

Since for Database relation R(a, b, c, d) all values are atomic and

Here neither of a, b, c, d are primary key.
The primary key is 'ab‘ prime attributes = {a, b} here part of key (a in a → c and in b in b → d) is dependent on non key hence there is a partial dependency and the relation is not in 2 NF.
Hence (a) is the correct option

QUESTION: 5

Third normal form is inadequate in situations where the relation

Solution:

Third normal form is considered adequate for relational database design, it is inadequate in all situations with the relation having multiple, composes or overlapped candidate keys.

QUESTION: 6

Entity set TRANSACTION has the attributes transaction number, date, amount. Entity set ACCOUNT has the attributes account number, customer name, balance.
Q. Which is the discriminator of the weak entity?

Solution:

We can clearly see that transaction is the weak entity with the discriminator (key for weak entity) as transaction number. This discriminator is used to uniquely identify each transaction of a particular account.

QUESTION: 7

Entity set TRANSACTION has the attributes transaction number, date, amount. Entity set ACCOUNT has the attributes account number, customer name, balance.
Q. Which is the primary key of the weak entity?

Solution:

In order to identify each transaction of any account the key of strong entity with the addition of the discriminator of weak entity can be taken. Here [Account number, transaction number] act as the primary key of weak entity. This is because weak entity has no existence without strong entity.

QUESTION: 8

If a relation scheme is in BCNF, then it is also in

Solution:

BCNF is the more restrictive compared to 3NF. 3NF is more restrictive as compared to 2NF and so on.
Hence option (d) is correct.

QUESTION: 9

For relation R(A, B, C, D, E, F) the set of FD’s is {A → C, B → D, C →  E, D → E, E → A, F → B} What is the candidate key for R?

Solution:

According to the given set of functional dependencies

QUESTION: 10

A set of FDs is given for a relation R (A, B, C, D, E, F, G)

What is the closure of {A, C}+ under this set?

Solution:


Hence (d) is the correct option.