UGC NET Computer Science Unit 3 & 4 PYQs with Answers

UGC NET Computer Science Unit 3 and Unit 4 are among the most important sections of the syllabus, covering Computer Organisation & Architecture and Programming & Data Structures. These units frequently include conceptual, numerical, and problem-solving questions in the examination. 

Practising Previous Year Questions (PYQs) helps candidates understand recurring topics, identify high-weightage areas, and improve their problem-solving speed and accuracy. By regularly solving UGC NET Computer Science Unit 3 & 4 PYQs, aspirants can strengthen their fundamentals, improve accuracy, and gain confidence for the exam.

UGC NET Computer Science Unit 3 & 4 PYQs

UGC NET Computer Science Unit 3 & 4 Previous Year Questions (PYQs) are an effective tool for understanding the exam pattern and focusing on important concepts. PYQs from these units test both theoretical knowledge and practical problem-solving abilities.

1. Match List-I with List-II.

Choose the correct answer from the options given below:

• A) A-III, B-IV, C-II, D-I

• B) A-III, B-IV, C-I, D-II

• C) A-IV, B-III, C-II, D-I

• D) A-IV, B-II, C-I, D-III

Answer: A) A-III, B-IV, C-II, D-I
Explanation: Timestamp protocol ensures freedom from deadlock → III; Strict 2PL ensures cascadeless rollback → IV; Two-phase locking's lock point indicates the final lock → II; Lock point definition matches the "already running" description → I.

2. Match List-I with List-II.

• A) A-III, B-II, C-I, D-IV

• B) A-IV, B-I, C-II, D-III

• C) A-II, B-III, C-IV, D-I

• D) A-IV, B-I, C-III, D-II

Answer: B) A-IV, B-I, C-II, D-III
Explanation: BCNF → every FD implied by candidate keys; 5NF → every JD implied by candidate keys; 1NF → all domains contain scalar values only; 4NF → every MVD implied by candidate keys.

3. Find the number of tuples by applying the operation X⟕ X.S = Y.S^Y

• A) 1

• B) 3

• C) 4

• D) 6

Answer: C) 4
Explanation: The left outer join X⟕Y on X.S = Y.S keeps all tuples from X and matches with Y where S values match. J, B, R match in both tables (3 matches), and T has no match in Y but is still retained with NULLs — giving 4 total tuples.

4. Identify the incorrect statement(s).

• A) A candidate key is minimal set of one or more attributes that, taken collectively, allows us to uniquely identify any entity in the entity set.

• B) A candidate key for which no proper subset is also a candidate key is called a super key.

• C) A super key is a set of one or more attributes that, taken collectively, allows us to uniquely identify any entity in the entity set.

• D) A super key for which no proper subset is also a super key is called a candidate key.

Answer: B) A candidate key for which no proper subset is also a candidate key is called a super key.
Explanation: Statement B is incorrect because it has the definition reversed — it is actually a super key for which no proper subset is also a super key that is called a candidate key, not the other way around.

5. Given the following STUDENT-COURSE scheme: STUDENT (Rollno, Name, Courseno) COURSE (Courseno, Coursename, Capacity), where Rollno is the primary key of relation STUDENT and Courseno is the primary key of relation COURSE. Attribute Coursename of COURSE takes unique values only. The number of records in COURSE and STUDENT tables are 3 and 5 respectively. Following relational algebra query is executed: R = STUDENT X COURSE
   Match List-I with List-II in context to the above problem statement.

• A) A-III, B-I, C-IV, D-II

• B) A-I, B-III, C-IV, D-II

• C) A-I, B-III, C-IV, D-II

• D) A-I, B-III, C-II, D-IV

Answer: B) A-I, B-III, C-IV, D-II
Explanation: Degree of R = 3+3 = 6 attributes → III; Cardinality = 5×3 = 15 tuples → I; Foreign key of STUDENT is Courseno → IV; COURSE has no foreign key → NIL → II.

6. The following table has two attributes Employee_id and Manager_id, where Employee_id is a primary key and manager_id is a foreign key referencing Employee_id with an on-delete cascade:

On deleting the tuple (20, 40), the set of other tuples that must be deleted to maintain the referential integrity of the table is:

• A) (30, 35) only

• B) (30, 35) and (35, 20) only

• C) (35, 20) only

• D) (40, 45) and (25, 40) only

Answer: C) (35, 20) only
Explanation: Deleting Employee_id = 20 causes cascade delete on tuples where Manager_id = 20, which is (35, 20). Deleting Employee_id = 35 then cascades to tuples where Manager_id = 35, which is (30, 35). So the full set deleted is (35, 20) and (30, 35) → Answer: B) (30, 35) and (35, 20) only.

7. Which of the following key constraints is required for functioning of foreign key in the context of relational databases?

• A) Unique key

• B) Primary key

• C) Candidate key

• D) Check key

Answer: B) Primary key
Explanation: A foreign key must reference a primary key in the parent table, as the primary key constraint ensures uniqueness and non-nullability, which are both required for the referential integrity enforced by foreign keys.