Re: Functional Dependencies

In a MVD (X ->> Y), Y can be a fixed set of values

X Y

X1 {Y1, Y2}
X2 {Y3, Y4}
X1 {Y1, Y2}

A FD is essentially a stronger form of MVD (with a single value requirement, as opposed to a set). So, all FDs can be considered MVDs, if the entire set is considered to be a single value, but a MVD is not necessarily a FD. That is, in all cases X -> Y |= X ->> Y, but X ->> Y \> X -> Y, because:

(X ->> Y)

X Y