Definition


Let X and Y be sets of explicit attributes of a temporal relation schema, R. A temporal functional dependency, denoted X$\;\stackrel{{\mbox{\rm\tiny T}}}{{\rightarrow}}\;$Y, exists on R if, for all instances r of R, all snapshots of r satisfy the functional dependency X→Y.

Note that more specific notions of temporal functional dependency exist for valid-time, transaction-time, bitemporal, and spatiotemporal relations. Also observe that using the template for temporal functional dependencies, temporal multivalued dependencies may be defined in a straight-forward manner.

Finally, the notions of temporal keys (super, candidate, primary) follow from the notion of temporal functional dependency.