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Integrity Constraints and Normal Forms

GATE CSE 2014 Set 1 · Q30

MCQ2 marksMedium

Time

Given the following two statements: S1: Every table with two single-valued attributes is in 1NF, 2NF, 3NF and BCNF. S2: AB→C,D→E,E→CAB\rightarrow C, D\rightarrow E, E\rightarrow C is a minimal cover for the set of functional dependencies AB→C,D→E,AB→E,E→CAB\rightarrow C, D\rightarrow E, AB\rightarrow E, E\rightarrow C. Which one of the following is CORRECT?

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Solution

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Official answer: A) S1 is TRUE and S2 is FALSE.

Integrity Constraints and Normal Forms

Evaluating Statement S1:

  • Any relational schema with two single-valued attributes R(A,B)R(A, B) is inherently in 1NF.

  • The possible non-trivial functional dependencies are:

    1. A→BA \rightarrow B: Then AA is a candidate key, so the LHS is a superkey.

    2. B→AB \rightarrow A: Then BB is a candidate key, so the LHS is a superkey.

    3. Both A→BA \rightarrow B and B→AB \rightarrow A: Both AA and BB are candidate keys (superkeys).

    4. No non-trivial dependencies: The candidate key is ABAB.

  • In all cases, for every non-trivial functional dependency X→YX \rightarrow Y, XX is a superkey. Therefore, every two-attribute relation is always in BCNF (and consequently in 1NF, 2NF, and 3NF).

  • Thus, S1 is TRUE.

Evaluating Statement S2:

  • Given original set of FDs F={AB→C, D→E, AB→E, E→C}F = \{AB \rightarrow C,\ D \rightarrow E,\ AB \rightarrow E,\ E \rightarrow C\}.

  • To find a minimal (canonical) cover:

    1. Check for redundant dependencies:

      • For AB→CAB \rightarrow C: Using the other FDs {D→E,AB→E,E→C}\{D \rightarrow E, AB \rightarrow E, E \rightarrow C\}, compute (AB)+(AB)^+:

        (AB)+={A,B,E,C}(AB)^+ = \{A, B, E, C\}

        Since C∈(AB)+C \in (AB)^+, AB→CAB \rightarrow C is redundant and can be removed.

    2. The remaining set is F′={D→E, AB→E, E→C}F^{\prime} = \{D \rightarrow E,\ AB \rightarrow E,\ E \rightarrow C\}.

    3. Testing for extraneous attributes on the LHS of AB→EAB \rightarrow E shows neither AA nor BB can be dropped.

  • Thus, a minimal cover for FF is {D→E, AB→E, E→C}\{D \rightarrow E,\ AB \rightarrow E,\ E \rightarrow C\}.

  • The set given in S2, {AB→C, D→E, E→C}\{AB \rightarrow C,\ D \rightarrow E,\ E \rightarrow C\}, is missing AB→EAB \rightarrow E (which cannot be derived from this set because (AB)+={A,B,C}(AB)^+ = \{A, B, C\} does not contain EE). Hence it is not equivalent to FF.

  • Thus, S2 is FALSE.

Therefore, S1 is TRUE and S2 is FALSE (Option A).

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This Integrity Constraints and Normal Forms previous year question is Q30 of the GATE CSE 2014 Set 1 paper. Find more GATE CSE PYQs on Integrity Constraints and Normal Forms in Databases, or browse all GATE CSE PYQs.

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Integrity Constraints and Normal Forms in GATE CSE

Integrity Constraints and Normal Forms has 30 GATE CSE PYQs across 20 papers from 2011 to 2026. 7 of them are 2-mark MCQs like this one, and GATE CSE 2014 Set 1 has 2.

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GateAI solution cardGATE CSE 2014 Set 1 · Q30 · MCQ

Given the following two statements: S1: Every table with two single-valued attributes is in 1NF, 2NF, 3NF and BCNF. S2: AB→ C, D→ E, E→ C is a minimal cover for the set of functional dependencies AB→ C, D→ E, AB→ E, E→ C. Which one of the following is CORRECT?

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.