DATABASE

Question

A table R is in 3NF if whenever a nontrivial functional dependency X-->A holds in R then X and A must satisfy which condition?

Answer 1

https://en.wikipedia.org/wiki/Third_normal_form

 a table is in 3NF if and only if, for each of its functional dependencies X → A, at least one of the following conditions holds:

• X contains A (that is, X → A is trivial functional dependency), or
• X is a superkey, or
• Every element of A-X, the set difference between A and X, is a prime attribute (i.e., each attribute in A-X is contained in some candidate key)

Answer 2

non trivial FD X → A is in 3NF

iff

1) R must be in 2nd Normal Form

2) X is super key (or )A is prime attribute