Problem identifying why a relation is not in 3NF
I am currently attempting to learn som rudimentary database stuff and I am stuck on this question; Given a relation R(A, B, C) with Fd´s: {A>C,B>C} why is R not in 3nf?
So the candidate key here is obviously AB, but I am not sure why this shouldnt be in 3NF since there is seemingly no transitive dependancies or partial dependencies since C depends upon both A and B (albeit seperately).
Am I completely off base here?
1 answer

There are different equivalent definitions of 3NF. One of them is that for each nontrivial functional dependency, either the determinant (left hand side attributes) is a superkey, or any attribute of the determinate (right hand side attributes) is prime (i.e. is part of any candidate key).
And since both A→C and B→C violates this definition, (A and B are not superkeys, and C is a not prime), the relation is not in 3NF.
The relation is neither in 2NF, since the dependency AB→C is a partial dependency: in fact we can remove either A or B and the dependency still holds.