Search for candidate keys from relationship data

Question

I am doing some research on this issue and cannot find the answer.

R = (A, B, C, D, E) 

Functional Dependencies:

 A => B ED => A BC => E 

He then lists the candidate keys as:

 ACD, BCD, CDE 

How do these candidate keys come from the above FDs?

Similarly, where R = (A, B, C, D) :

Functional Dependencies:

 D => B AB => D AB => CC=> A 

He then lists the candidate keys as:

 AB, BC, CD, AD 

Again, my problem here is that I'm not sure how the candidate keys were obtained from FD?

Thank you in advance.

Answer 1

This article describes how confection keys are derived from a given relationship.
http://en.wikipedia.org/wiki/Candidate_key .
Also take a look: functional dependency candidate keys
functional dependencies.
This is also good, I think:
http://www.cs.newpaltz.edu/~pletcha/BuildingCandidateKeys.html

so basically:
A => B (first case):
ED => A
BC => E
Since C and D are independent of any fd, it is obvious that CD is part of each denomination key.

ACD, BCD, CDE
The second:
D => B
AB => D
AB => C
C => A

All singles depend on one of fd, therefore, none of them is included in all candy keys.
And it does not depend on D, but not on B, not explicit or implicit. SO AD and AB are one
key. B is independent of C and A; therefore, AB and BC. C is independent of D, therefore CD.

AB, BC, CD, AD

this is also useful: http://csc.lsu.edu/~jianhua/fd_slide2_09.pdf