Engineering Questions with Answers - Multiple Choice Questions

# Database MCQ – Functional-Dependency Theory

1 - Question

We can use the following three rules to find logically implied functional dependencies. This collection of rules is called
a) Axioms
b) Armstrong’s axioms
c) Armstrong
d) Closure

Explanation: By applying these rules repeatedly, we can find all of F+, given F.

2 - Question

Which of the following is not Armstrong’s Axiom?
a) Reflexivity rule
b) Transitivity rule
c) Pseudotransitivity rule
d) Augmentation rule

Explanation: It is possible to use Armstrong’s axioms to prove that Pseudotransitivity rule is sound.

3 - Question

The relation employee(IDemployee1 (ID, name)
employee2 (name, street, city, salary)
This type of decomposition is called
a) Lossless decomposition
b) Lossless-join decomposition
c) All of the mentioned
d) None of the mentioned,name,street,Credit,street,city,salary) is decomposed into

Explanation: Lossy-join decomposition is the decomposition used here .

4 - Question

Inst_dept (ID, name, salary, dept name, building, budget) is decomposed into

instructor (ID, name, dept name, salary)
department (dept name, building, budget)
This comes under
a) Lossy-join decomposition
b) Lossy decomposition
c) Lossless-join decomposition
d) Both Lossy and Lossy-join decomposition

Explanation: Lossy-join decomposition is the decomposition used here .

5 - Question

There are two functional dependencies with the same set of attributes on the left side of the arrow:
A->BC
A->B
This can be combined as
a) A->BC
b) A->B
c) B->C
d) None of the mentioned

Explanation: This can be computed as the canonical cover.

6 - Question

Consider a relation R(A,B,C,D,E) with the following functional dependencies:

ABC -> DE and
D -> AB
The number of superkeys of R is:
a) 2
b) 7
c) 10
d) 12

Explanation: A superkey is a combination of columns that uniquely identifies any row within a relational database management system (RDBMS) table.

7 - Question

Suppose we wish to find the ID’s of the employees that are managed by people who are managed by the employee with ID 123. Here are two possible queries:

I.SELECT ee.empID
FROM Emps ee, Emps ff
WHERE ee.mgrID = ff.empID AND ff.mgrID = 123;
II.SELECT empID
FROM Emps
WHERE mgrID IN
(SELECT empID FROM Emps WHERE mgrID = 123);
Which, if any, of the two queries above will correctly (in SQL2) get the desired set of employee ID’s?
a) Both I and II
b) I only
c) II only
d) Neither I nor I

Explanation: The query can be satisfied by any of the two options.

8 - Question

Suppose relation R(A,B) currently has tuples {(1,2), (1,3), (3,4)} and relation S(B,C) currently has {(2,5), (4,6), (7,8)}. Then the number of tuples in the result of the SQL query:

SELECT *
FROM R NATURAL OUTER JOIN S;
IS:
a) 2
b) 4
c) 6
d) None of the mentioned

Explanation: The SQL NATURAL JOIN is a type of EQUI JOIN and is structured in such a way that, columns with same name of associate tables will appear once only.

9 - Question

Suppose now that R(A,B) and S(A,B) are two relations with r and s tuples, respectively (again, not necessarily distinct). If m is the number of (not necessarily distinct) tuples in the result of the SQL query:

R intersect S;
Then which of the following is the most restrictive, correct condition on the value of m?
a) m = min(r,s)
b) 0 <= m <= r + s
c) min(r,s) <= m <= max(r,s)
d) 0 <= m <= min(r,s)

Explanation: The value of m must lie between the min value of r and s and 0.

10 - Question

Suppose relation R(A,B,C,D,E) has the following functional dependencies:

A -> B
B -> C
BC -> A
A -> D
E -> A
D -> E
Which of the following is not a key?
a) A
b) E
c) B, C
d) D