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 start/finish points of modeled events are precisely known. In many real life situations, however, the time boundary of events and the duration of entity relationships may not be exactly known. Modeling these situations and providing a way to write queries dealing with time impreciseness represents a useful extension currently lacking in existing/proposed temporal database systems. In this paper, we discuss the problem of handling time impreciseness in temporal databases and present three models for the representation of imprecise time intervals. We illustrate the basic idea and motivation of each model, its underlying logic, tradeoffs, and important properties. We also propose query language extensions that can enrich the user interface with capabilities to formulate queries dealing with time impreciseness. Extensions to existing query constructs at both the transaction level and the operator level are presented. New operators related to time impreciseness are also presented. The models and extensions discussed in this paper enrich the flexibility of temporal databases and can be used to help users obtain more meaningful replies for their temporal queries.