A Retrospective Analysis of Time Concepts in Temporal Databases

In this paper, we propose a formal de nition of temporal validity which we believe is the rst and the most comprehensive quanti cation of that notion. The temporal validity is developed into the notion of sort of validity with which the confusion among various time concepts introduced for temporal databases can be dispelled. Further, we discuss the problem of preserving multiple past states of a temporal database, which leads to the identi cation of a maximal set of time concepts and multidimensional representations. It is shown that the time concept, event time is needed to properly model retroactive and proactive updates, as it is not possible to model them using the valid and transaction times as thought earlier. We also show the adequacy of three time concepts (valid time, event time and transaction time) for completely preserving di erent past states generated by retroactive and proactive updates, error corrections, and delayed updates.