Comparing Functional Dependencies

Functional dependencies: a statement about the set of allowable

databases.

Entailment and equivalence: comparing sets of functional dependencies

Entailment: a set of functional dependencies S1 entails a set S2 if:

any database that satisfies S1 much also satisfy S2.

Example: {A B, B C}

entails

A C

Equivalence: two sets of FD’s are equivalent if each entails the

other.

{A B, B C } is equivalent to {A B, A C, B C}