Let R (ABCDEFGH) be a relation schema and F be the set of dependencies 𝐹 =…
2022
Let R (ABCDEFGH) be a relation schema and F be the set of dependencies 𝐹 = {𝐴→𝐵,𝐴𝐵𝐶𝐷→𝐸,𝐸𝐹→𝐺,𝐸𝐹→𝐻 and 𝐴𝐶𝐷𝐹→𝐸𝐺}. The minimal cover of a set of functional dependencies is
- A.
𝐴→𝐵,𝐴𝐶𝐷→𝐸,𝐸𝐹→𝐺, and 𝐸𝐹→𝐻
- B.
𝐴→𝐵,𝐴𝐶𝐷→𝐸,𝐸𝐹→𝐺,𝐸𝐹→𝐻 and 𝐴𝐶𝐷𝐹→𝐺
- C.
𝐴→𝐵,𝐴𝐶𝐷→𝐸,𝐸𝐹→𝐺,𝐸𝐹→𝐻 and 𝐴𝐶𝐷𝐹→𝐸
- D.
𝐴→𝐵,𝐴𝐵𝐶𝐷→𝐸,𝐸𝐹→𝐻 and 𝐸𝐹→𝐺
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Correct answer: A
Compute the minimal cover for F = {A→B, ABCD→E, EF→G, EF→H, ACDF→EG}.
Step 1: Split right-hand sides so each dependency has a single attribute on the right.
A→B
ABCD→E
EF→G
EF→H
ACDF→E
ACDF→G
Step 2: Minimize left-hand sides by removing any extraneous attributes.
Check ABCD→E: test if B is extraneous. Compute closure of {A,C,D}: A gives B (A→B), so {A,C,D}+ contains B, then ABCD→E yields E. Hence B is extraneous and ABCD→E reduces to ACD→E.
Step 3: Remove redundant dependencies.
ACDF→E is implied by ACD→E because ACDF contains ACD, so ACDF→E is redundant.
ACDF→G is implied as follows: ACDF gives E (via ACD→E) and with F present we have EF, and EF→G gives G. Thus ACDF→G is redundant.
Final minimal cover:
A→B
ACD→E
EF→G
EF→H
This matches the minimal cover provided in the correct option.
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