A temporal tuple is temporally homogeneous if the lifespan of all attribute values within it are identical. A temporal relation is said to be temporally homogeneous if its tuples are temporally homogeneous. A temporal database is said to be temporally homogeneous if all its relations are temporally homogeneous. In addition to being specific to a type of object (tuple, relation, database), homogeneity is also specific to some time dimension, as in ``temporally homogeneous in the valid-time dimension'' or ``temporally homogeneous in the transaction-time dimension.''
The motivation for homogeneity arises from the fact that no timeslices of a homogeneous relation produce null values. Therefore a homogeneous relational model is the temporal counterpart of the snapshot relational model without nulls. Certain data models assume temporal homogeneity. Models that employ tuple timestamping rather than attribute value timestamping are necessarily temporally homogeneous—only temporally homogeneous relations are possible.