On the completeness of temporal database query languages

Abstract

In this paper, we introduce a new definition of completeness for temporal query languages based on the relational model. Our definition relies on the following three notions: relational completeness of non-temporal queries as defined by Codd; the preservation of temporal irreducibility of temporal (valid time) relations, be they stored or returned as results of temporal queries; and the notion of temporal equivalence between temporal and non-temporal queries. Particularly important is the notion of temporal irreducibility which requires that the valid time intervals of two tuples with the same data values must not touch or overlap, since unreduced relations generate incorrect answers to certain types of temporal queries. Finally, we introduce the query language ChronoLog which is a temporally complete extension of Datalog.