On the Semantics of Transaction Time and Valid Time in Bitemporal Databases
40 Pages Posted: 31 Oct 2008
Date Written: December 1992
Abstract
Numerous proposals for extending the relational data model to incorporate the temporaldimension of data have appeared in the past several years. While most of thesehave been historical databases, incorporating in some fashion a valid time dimensionto the data model and the query languages, others have been rollback databases, incorporatinga transaction time dimension, or bitemporal databases, incorporating both ofthese temporal dimensions. In this paper we address an issue that has been lacking inmany of these papers, namely, a formal specification of the precise semantics of thesetemporal dimensions of data. We introduce the notion of reference time - the timethat any operation is applied to the database state - and provide a logical analysisof the interrelationships among these three temporal dimensions. We also provide ananalysis of the meaning of various variables such as now and â which have been usedin many of these models without a complete specification of their semantics.
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