ATabase> Given a relATion R (in a relATional dATabase), ATtribute Y of R is functionally dependent on ATtribute X of R and X of R functionally determines Y of R (in symbols R.X -> R.Y) if and only if each X in R has associATed with it precisely one Y in R (AT any one time). ATtributes X and Y may be composite. This is very close to a function in the mAThemATical sense. (1997-09-01)