Question

R(A, B, C, D) with FDs A ? B, B ? C, B ? D
(1) What are all the nontrivial FD’s that follow from the given FD’s? You should restrict yourself to FD’s with single attributes on the right side.
(2) What are all the keys of R?
(3) What are all the superkeys for R that are not keys?

Answer 1

1)

A --> C, A --> D

2)

{A, B} is key

3)

C and D

Answer 2

Consider a relation with schema R(A, B, C, D) and FD's AB->C, C->D, and D->A.
a) What are all the nontrivial FD's that follow from the given FD's? You should restrict yourself to
FD's with single attributes on the right side.
b) What are all the keys of R?
c) What are all the superkeys for R that are not keys?

Alright so its been a while since ive taking this course and im trying to help a friend with his assignment but im getting confused. For part A, its askingfor all non trivial dependencies, now as i remember it a trivial dependency is a dependency X->Y where Y is a subset of X. So then would all the givenFDs be non trivial since the right side of the FDs is not contained in the left side.

Anyways any assistance with this would be great, especially if someone has an example of this type of question to look at for reference. Ive tried a fewpowerpoints found on goole but they dont seem to show any good examples just an explanation of what trivial and FDs are.