2023 question paper

DATABASE MANAGEMENT SYSTEM

5 questions

1. Q1a. A row from a table is selected by - (i) selection operator - (ii) projection operator - (iii) union operator - (iv) none of these20232m

   Unit 2: Relational Query Languages

   A row from a table is selected by

   • (i) selection operator
   • (ii) projection operator
   • (iii) union operator
   • (iv) none of these

   View this question on its own page →

   CopySearch GoogleAsk AI

   Worked Solution

   Answer: (i) selection operator

   Explanation: In relational algebra, selection (sigma) selects rows/tuples satisfying a condition horizontally. Projection (pi) selects columns/attributes vertically. Union combines tuples from two compatible relations. So row selection is via selection operator, e.g., sigma_{age>20}(Student).

2. Q1b. A normal form in which every non-prime attribute is fully dependent on prime attribute is - (i) 1 NF - (ii) 2 NF - (iii) 3 NF - (iv) BCNF20237m

   Unit 2: Relational Query Languages

   A normal form in which every non-prime attribute is fully dependent on prime attribute is

   • (i) 1 NF
   • (ii) 2 NF
   • (iii) 3 NF
   • (iv) BCNF

   View this question on its own page →

   CopySearch GoogleAsk AI

   Worked Solution

   Answer: (ii) 2 NF

   Explanation: 1NF - atomic values, no repeating groups.
   2NF - is in 1NF and every non-prime attribute is fully functionally dependent on the primary key (no partial dependency where non-prime depends on part of composite key).
   3NF eliminates transitive dependency (non-prime depends on another non-prime).
   BCNF is stronger 3NF where every determinant is a superkey.

   The description "every non-prime attribute is fully dependent on prime attribute" actually describes 2NF partial dependency removal (taught as 2NF definition). Hence answer is 2NF. Note: strict formal definition: In 2NF, no non-prime attribute is partially dependent on any candidate key.

3. Q1c. Serializability of concurrent transaction is ensured by - (i) locking - (ii) time stamping - (iii) both (a) and (b) - (iv) none of these20232m

   Unit 3: Storage and Transaction Processing

   Serializability of concurrent transaction is ensured by

   • (i) locking
   • (ii) time stamping
   • (iii) both (a) and (b)
   • (iv) none of these

   View this question on its own page →

   CopySearch GoogleAsk AI

   Worked Solution

   Answer: (iii) both (a) and (b)

   Explanation: Serializability (conflict or view) can be ensured by both locking protocols (2PL, strict 2PL) and timestamp ordering protocols. Locking prevents conflicting operations via locks; timestamping orders transactions by timestamps. Either mechanism or hybrid can guarantee serializability. Option checks "both locking and time stamping" as valid concurrency control methods.

4. Q1d. Which key cannot be null - (i) Unique key - (ii) Primary key - (iii) Super key - (iv) Foreign key20237m

   Unit 1: Database System Architecture

   Which key cannot be null

   • (i) Unique key
   • (ii) Primary key
   • (iii) Super key
   • (iv) Foreign key

   View this question on its own page →

   CopySearch GoogleAsk AI

   Worked Solution

   Answer: (ii) Primary key

   Explanation: Primary key cannot be NULL and must be unique - entity integrity constraint. Unique key can have one NULL (in many DBMS) but cannot duplicate. Super key is any set of attributes that uniquely identifies row, may include extra attributes. Foreign key can be NULL (if relationship optional) - referential integrity allows NULL.

5. Q1e. BCNF stands for - (i) Boyle Cold Normalization Form - (ii) Boyce Cold Normal Form - (iii) Boyce Codd Normal Form - (iv) None of these20232m

   Unit 2: Relational Query Languages

   BCNF stands for

   • (i) Boyle Cold Normalization Form
   • (ii) Boyce Cold Normal Form
   • (iii) Boyce Codd Normal Form
   • (iv) None of these

   View this question on its own page →

   CopySearch GoogleAsk AI

   Worked Solution

   Answer: (iii) Boyce Codd Normal Form

   Explanation: BCNF = Boyce-Codd Normal Form (stronger than 3NF). Developed by Raymond Boyce and Edgar Codd. Condition: For every functional dependency X -> Y, X is a superkey. Options (i) and (ii) are distractors with misspelling.