A Novel Approach to Model NOW in Temporal Databases

In bitemporal databases, current facts and transaction states are modelled using a special value to represent the current time (such as a minimum or maximum timestamp or NULL). Previous studies indicate that the choice of value for now (i.e. the current time) significantly influences the efficiency of accessing bitemporal data. This paper intro-duces a new approach to represent now, in which current tuples and facts are represented as points on the transac-tion time and valid time line respectively. This allows us to exploit the computational advantages of point-based query languages. Via an empirical study, we demonstrate that our new approach to representing now offers considerable performance benefits over existing techniques for accessing bitemporal data.