functional dependency

from The Free On-line Dictionary of Computing (8 July 2008)

functional dependency

   <database> 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)