relational-algebrafunctional-dependencies
How to specify a set of equivalent Functional Dependencies for a given relation
We've been told that the FD are:
A->B
B->C
C->A
But with the transitive rule, since A->B and B->C this also means:
A->C
I worked out that:
A->BC is true, since A->B and A->C are FD. I can split A->BC to A->B, A->C with the splitting rule
C->AB is true, since C->A and due to transit rule: C->B is true (where C->A, A->B means C->B)
Can someone tell me the correct answer and why my answer is wrong. I can't get my head round the given answer.
Solution
The discussion of why your answer is wrong can be found in the comments.
The correct answer is #4: only in this answer A, B and C are superkeys as in the original set of functional dependencies. In #1 A is not a superkey (e.g., A -> B does not hold), in #3 C is not a superkey (e.g., C -> B does not hold).
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