Prescription for Modelling Time in Databases

] The prevailing approach to modelling the time dimension in databases is, in one form or another, the use of an explicit representation of time. In this paper we propose a temporal relational model and algebra, based on temporal semantics, to incorporate an implicit time dimension in databases. In temporal semantics, time-varying relations are an indexed collection of ordinary relations, one for each moment in time. A temporal database is modelled by a collection of time-varying relations. Temporal databases are queried using a temporal relational algebra (Tra) which extends the relational algebra point-wise upon the set of natural numbers. We also give examples of time-speciic and time-relative queries, and of combining time-varying data by temporal intersection, union and splicing. Although Tra lacks the ability to explicitly manipulate time, we show how temporal aggregation and when-type queries can be formulated using a technique called \tagging".