Database-Management-System
August 29, 2024Database-Management-System
August 29, 2024Database-Management-System
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Question 309
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Let R = {A, B, C, D, E, F} be a relation schema with C → F, E → A, EC → D and
A→ B. Which of the following is a key for R?
A→ B. Which of the following is a key for R?
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CD
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EC
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AE
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AC
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Question 309 Explanation:
ABDF is present at the right side of productions. So check for the CE
CE – CE // CE derives CE
CEF // C derives F
CEFA // E derives A
CEFAB // A derives B
CEFABD // EC derives D
So the key for R is “ EC”
(EC)+ = { A,B,C,D,E,F}
(CD)+ = {C,D,F}
(AE)+ = {A,B,E}
(AC)+ = {A,C,F,B}
CE – CE // CE derives CE
CEF // C derives F
CEFA // E derives A
CEFAB // A derives B
CEFABD // EC derives D
So the key for R is “ EC”
(EC)+ = { A,B,C,D,E,F}
(CD)+ = {C,D,F}
(AE)+ = {A,B,E}
(AC)+ = {A,C,F,B}
Correct Answer: B
Question 309 Explanation:
ABDF is present at the right side of productions. So check for the CE
CE – CE // CE derives CE
CEF // C derives F
CEFA // E derives A
CEFAB // A derives B
CEFABD // EC derives D
So the key for R is “ EC”
(EC)+ = { A,B,C,D,E,F}
(CD)+ = {C,D,F}
(AE)+ = {A,B,E}
(AC)+ = {A,C,F,B}
CE – CE // CE derives CE
CEF // C derives F
CEFA // E derives A
CEFAB // A derives B
CEFABD // EC derives D
So the key for R is “ EC”
(EC)+ = { A,B,C,D,E,F}
(CD)+ = {C,D,F}
(AE)+ = {A,B,E}
(AC)+ = {A,C,F,B}