Assume a temporal relation where the attribute values of tuples are (partial) functions from some time domain to value domains. A tuple in such a relation is temporally homogeneous if the domains of all its attribute values are identical. A temporal relation is temporally homogeneous if all its tuples are temporally homogeneous. Likewise, a temporal database is 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 a time dimension when the time domain is multidimensional, 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...
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