## NPTEL Introduction to Database Systems Week 3 Assignment Answers 2024

1. Some relations may not have a key.

- True
- False

Answer :-For AnswerClick Here

2. An attribute name should not be used in more than one relation.

- True
- False

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3. A key of a relation may have more than one attribute.

- True
- False

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4. The elements of the domain of an attribute may be ordered pairs of values.

- True
- False

Answer :-

5. Some relations may not have a foreign key.

- True
- False

Answer :-

6. A foreign key in a relation should consist of exactly one attribute.

- True
- False

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7. A foreign key in a relation R can NOT be used to refer to tuples in R itself.

- True
- False

Answer :-

8. If A is a foreign key in R, no null values are permitted in the column A in any instance of R.

- True
- False

Answer :-

9. Suppose A is a foreign key in R that refers to tuples of S using values of the key attribute B of S. Let X be the set of all non-null values of

column A and let Y be the set of all values of column B. Identify the correct relationship between X and Y that holds in

all instances of R and S:

- X is a subset of Y
- X is a proper subset of Y
- Y is a subset of X
- X need not be a subset of Y and Y need not be a subset of X

Answer :-

10. Consider the following relations S1(P,Q,R) and S2(T,U,V) and the given instances. What is the result of the relational algebra expression

- Empty relation
- { (2,4), (3,6) }
- A relation with scheme (P,Q) and tuples { (1,2) }
- A relation with scheme (P,Q) and tuples { (1,2), (2,4), (3,6) }

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11.

Using the relation instances given in the Question 10, find out how many tuples will be there in the result of the following relational algebra expression:

` S1⋈S1.Q≥S2.VS2`

- 20
- 9
- 8
- 16

Answer :-

12. Consider the four relations R1(A, B, C), R2(X, Y, Z), R3(A, B, D) and R4(U, X, Y). The domains of the attributes are: A – integers;

B – strings; C – single characters; D – { ‘M’, ‘F’ }; U – integers; X – strings; Y – single characters; Z – { ‘M’, ‘F’ }. Identify the

pair of union-compatible relations:

- Pair R1, R3
- Pair R1, R4
- Pair R2, R3
- Pair R3, R4

Answer :-

13. The join relational algebra operator can NOT be expressed using other operators.

- True
- False

Answer :-

14. The cross product relational algebra operator requires its operands to be union-compatible.

- True
- False

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15. The difference relational algebra operator requires its operands to be union-compatible.

- True
- False

Answer :-

16. When project is applied on an instance r , the size of the result will always be the same as that of r.

- True
- False

Answer :-

17. Consider the following relations S1(P,Q,R) and S2(P,R) and the given instances. What is the result of the relational algebra expression?

- Empty relation
- A relation with scheme (Q) and tuples { (2), (4) }
- A relation with scheme (Q) and tuples { (2), (4), (6) }
- { 2, 4 }

Answer :-

18. Consider the following relation S1 and its given instance. What is the size of the result of the following relational algebra expression

on the relation S1?

- 5
- 6
- 7
- 8

Answer :-For AnswerClick Here

19. On the same relation given in Question 18, what is the size of the result of the following relational algebra expression?

- 9
- 10
- 11
- 12

Answer :-For AnswerClick Here