Temporal Connectives Versus Explicit Timestamps to Query Temporal Databases

Temporal databases can be queried either by query languages work ing directly on a timestamp representation or by languages using an implicit access to time via temporal connectives We study the dif ferences in expressive power between these two approaches First we consider temporal and rst order logic We show that future tem poral logic is strictly less powerful than past future temporal logic and also that there are queries expressible in rst order logic with ex plicit timestamps that are not expressible in extended temporal logic Our proof technique is novel and based on communication complex ity Then we consider extensions of rst order logic with xpoints or while loops Again the explicit temporal version of these languages using timestamps is compared with an implicit one using instruc tions for moving in time We also compare the temporal versions of the xpoint language with those of the while language Preliminary reports on this work were presented at the International Workshop on Temporal Databases Z urich September and the th ACM Symposium on Princi ples of Database Systems Montreal June Address Domaine de Voluceau B P F Le Chesnay Cedex France E mail serge abiteboul inria fr and laurent herr inria fr Address LUC Department WNI B Diepenbeek Belgium E mail vd buss luc ac be