Definition
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.”
Key Points
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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Recommended Reading
Gadia SK. A homogeneous relational model and query languages for temporal databases. ACM Trans Database Syst. 1988;13(4):418–48.
Jensen CS, Dyreson CE, editors. A consensus glossary of temporal database concepts – February 1998 version. In: Etzion O, Jajodia S, Sripada S, editors. Temporal databases: research and practice. Berlin: Springer; 1998. p. 367–405.
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Jensen, C.S., Snodgrass, R.T. (2018). Temporal Homogeneity. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_1421
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