Extending temporal query languages to handle imprecise time intervals

Previous work on temporal and historical databases has been mainly based on the assumption that the time intervals of temporal attributes and the star t/finish points of modeled events are precisely known. In many real life si tuations, however, the time boundary of events and the duration of entity r elationships may not be exactly known. Modeling these situations and provid ing a way to write queries dealing with time impreciseness represents a use ful extension currently lacking in existing/proposed temporal database syst ems. In this paper, we discuss the problem of handling time impreciseness i n temporal databases and present three models for the representation of imp recise time intervals. We illustrate the basic idea and motivation of each model, its underlying logic, tradeoffs, and important properties. We also p ropose query language extensions that can enrich the user interface with ca pabilities to formulate queries dealing with time impreciseness, Extensions to existing query constructs at both the transaction level and the operato r level are presented. New operators related to time impreciseness are also presented. The models and extensions discussed in this paper enrich the fl exibility of temporal databases and can be used to help users obtain more m eaningful replies for their temporal queries. (C) 1999 Elsevier Science Ltd . All rights reserved.