Friday, November 6, 2020

Quiz questions in database management systems with answers 11

MCQ on various aspects in DBMS including database introduction, user types, join techniques, 2PL and non-trivial multivalued dependency questions with answers, RDBMS Multiple Choice Questions with Answers

Database Management Systems (DBMS) MCQ Quiz Questions with Answers

1. How many non-trivial multi-valued dependencies are possible in a three attribute relation?

a) 3

b) 1

c) 2

d) 6

Answer: (d) 6

A non-trivial multi-valued dependency can involve only two attributes. Therefore, each dependency has one attribute on the left and one on the right. There are six such dependencies.

Let us see an example; R(A, B, C)

The possible non-trivial multi-valued dependencies are;

{A ->-> B, A ->-> C, B ->-> A, B ->-> C, C ->-> A, C ->-> B}

What is non-trivial functional dependency?

A functional dependency A B is said to be non-trivial if B is not subset or equal to A.


2. Which of the following is/are true?

a) 4NF implies BCNF

b) 4NF implies 3NF

c) 3NF implies 4NF

d) 3NF implies BCNF

Answer: (a) 4NF implies BCNF and (b) 4NF implies 3NF

Every 4NF relation is also in BCNF.

Every 4NF relation is also in 3NF.


3. Assume that a relation R has n tuples and S has m tuples. As per set-theoretic semantics, what will be the maximum number of tuples that R – S can have?

a) n

b) m

c) n + m

d) n * m

Answer: (a) n

R – S is set difference operation. This results in the tuples that are only in R and not in S. Hence, the maximum number of tuples that result from a set difference operation is the number of tuples in left operand (in this case, R).


4. Two Phase Locking (2PL) protocol

a) guarantees serializability

b) prevents deadlock

c) locks data items whenever required

d) ensures that lock operations precedes unlock operations

Answer: (a) guarantees serializability and (d) ensures that lock operations precedes unlock operations

2PL is a concurrency control protocol that ensures serializability.

It never acquire new locks after a lock is released. It locks data item in the growing phase and releases in shrinking phase. Once in shrinking phase, it never acquires new locks.


5. Consider relations r(A, B) and s(B, C). Assume that r contains 200 records, and that s contains 500 records. Without any further assumptions, what is the maximum number of tuples that r JOINr.B = s.B s can have?

a) 200

b) 100000

c) 500

d) 700

Answer: (b) 100000

r JOINr.B = s.B s is a theta join operation. That is, two relations joined on a common attribute.

If a relation r has n tuples and s has m tuples, then the maximum number of tuples results for a theta join is n * m.

The above statement is true if the values of attribute B of relation r is subset of attribute B of relation s.


Related posts:

Quiz questions with answers on DBMS introduction concepts

Solved quiz questions on user types and database access

MCQ with answers on relational model

4NF, BCNF, non-trivial multivalued dependency


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