Question on functional dependency

I am reading the following:

In a functional dependency X --> Y

the value of Y is *determined* by the X component.

and the value of X uniquely determines the value of Y.

Then I read

It is NOT true to say:

" Since X functionally determines Y, if we know X we know Y."
or
"If X identifies Y then X identifies Y"

(University of Virginia slide)

I'm not clear on how X can uniquely determine Y but not functionally determine or identify
Y

Semantics? Received on Tue Sep 21 2004 - 19:26:34 CDT