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)