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📊 Database Management System

MAKAUT B.Tech (PCC-CS601) 2024–25 – Detailed Solutions

✅ Group-A (1 Mark) | Group-B (5 Marks) | Group-C (15 Marks) | Exam-ready answers
📌 Group-A (Very Short Answer – 1 Mark Each)
(i) What is a Multivalued Attribute in an ERD?

Answer: An attribute that can have multiple values for a single entity. Example: Phone_Number of a student.

(ii) Are NULL values equivalent to zero or blank space?

Answer: No. NULL represents unknown or missing data and is different from zero or blank space.

(iii) In which indexing, the total number of records in both the index table and the database table is same?

Answer: Dense Indexing.

(iv) The two-phase locking (2PL) protocol consists of ______ phase and ______ phase.

Answer: Growing Phase and Shrinking Phase.

(v) What does RBAC stand for?

Answer: Role-Based Access Control.

(vi) What is the difference between homogeneous and heterogeneous DBMS?

Answer: Homogeneous: all sites use same DBMS; Heterogeneous: different sites use different DBMS.

(vii) What do you mean by Strong Entity in ER Diagram? Give an example.

Answer: An entity that has its own primary key and can exist independently. Example: Student(Student_ID, Name)

(viii) Which operator performs pattern matching in SQL?

Answer: LIKE

(ix) What is the main advantage of using sparse matrices for storing data?

Answer: Reduces memory/storage requirements by storing only non-zero values.

(x) Define Checkpoint used in Database Recovery.

Answer: A checkpoint is a recovery mechanism that saves the current database state to minimize recovery time after failure.

(xi) What does MAC stand for in Database Security?

Answer: Mandatory Access Control.

(xii) ______ refers to the act of maintaining duplicate copies of a database across multiple locations.

Answer: Replication.

✍️ Group-B (Short Answer – 5 Marks)
2. Which mechanisms are typically used to provide security in a database?

Mechanisms: Authentication, Authorization, Access Control, Encryption, Auditing, Backup & Recovery. Ensures confidentiality, integrity, availability.

3. Explain the types of data fragmentation in Distributed Database.

Horizontal fragmentation: rows divided (e.g., by location). Vertical fragmentation: columns divided. Mixed fragmentation: combination. Advantages: faster access, better security.

4. What do you mean by Generalization and Specialization? Give examples.

Generalization (bottom-up): Car, Bike → Vehicle. Specialization (top-down): Employee → Manager, Engineer.

5. Difference Between DROP, TRUNCATE and DELETE
DELETETRUNCATEDROP
Removes selected rows (WHERE allowed)Removes all rowsRemoves entire table
Table remainsTable remainsTable deleted
Can rollbackRollback possible usuallyCannot recover easily
6. Types of JOINs Supported by SQL

INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, SELF JOIN, CROSS JOIN.

📘 Group-C (Long Answer – 15 Marks)
7(a) Discuss ACID Properties with Example

Atomicity: all-or-nothing (fund transfer). Consistency: integrity maintained. Isolation: concurrent txns don't interfere. Durability: committed changes persist. Example: UPDATE balance SET balance=balance-1000 WHERE acc=101; and +1000 to acc=102; COMMIT.

7(b) How does a Dirty Read occur? Explain with Example.

Dirty read: reading uncommitted data. Example: T1 updates balance to 4000 (uncommitted), T2 reads 4000, then T1 rolls back → T2 used wrong value. Prevention: Serializable isolation, strict 2PL.

8(a) Explain Subsystems of Typical Database System Structure

Components: Query Processor, DDL Compiler, DML Compiler, Query Optimizer, Transaction Manager, Storage Manager, Buffer Manager. Diagram: Users → Query Processor → Transaction Manager → Storage Manager → Database Files.

8(b) Role of DBA Concerning Database Security

User account management, authentication, authorization, encryption, backup/recovery, audit trails, security policies. Ensures confidentiality, integrity, availability.

9(a) How does Data Abstraction help in DBMS?

Levels: Physical (storage), Logical (structure), View (user-specific). Advantages: reduced complexity, increased security, data independence, easier maintenance.

9(b) Explain Extended Features of ER Model

Specialization (top-down), Generalization (bottom-up), Aggregation (relationship as entity), Inheritance (subclass inherits). Example: Employee → Manager inherits Employee attributes.

10(a) Role of Keys in DBMS

Primary Key, Candidate Key, Alternate Key, Foreign Key, Composite Key. Importance: uniqueness, integrity, relationship, faster search, prevents duplication.

10(b) Degree of Relationship with Graphical Representation

Unary (degree 1): Employee supervises Employee. Binary (degree 2): Student enrolls in Course. Ternary (degree 3): Supplier supplies Part to Project.

Student ---- Enrolls ---- Course
11(a) Relational Algebra Queries

(i) MBA students: πStid,Stname(σCourse_Title='MBA'(Student ⋈ Course))
(ii) Instructors teaching both BTech(CSE) and BTech(IT): Intersection of two projections.
(iii) Duration longer than Prof S. Gupta: πInstructor_Name(σDuration > D(Instructor ⋈ Course)).

11(b) SQL Queries

(i) Students per course: SELECT Course_Id, COUNT(*) FROM Student GROUP BY Course_Id;
(ii) Same duration courses: SELECT C1.Course_Title, C2.Course_Title FROM Course C1, Course C2 WHERE C1.Duration=C2.Duration AND C1.Course_Id < C2.Course_Id;
(iii) Second highest marks in Network Security: using MAX subquery.

📖 Exam-focused Summary

✔ Complete coverage of MAKAUT DBMS (PCC-CS601) 2024–25 – all groups.
✔ Includes ER model, NULL values, indexing, 2PL, RBAC, fragmentation, generalization/specialization, ACID, dirty read, DBA roles, data abstraction, keys, relationship degree, relational algebra & SQL queries.
✔ Answers structured for 1, 5, and 15-mark questions with clear headings & exam-style presentation.

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