On the semantics of (Bi)temporal variable databases

Abstract

Numerous proposals for extending the relational data model to incorporate the temporal dimension of data have appeared during the past several years. These have ranged from historical data models, incorporating a valid time dimension, to rollback data models, incorporating a transaction time dimension, to bitemporal data models, incorporating both of these temporal dimensions. Many of these models have been presented in a non-traditional fashion, allowing the use of variables at the instance level. Unfortunately, the precise semantics of these database objects, e.g. tuples, with variables has not been made clear. In this paper we propose a framework for providing a formal specification of the precise semantics of this type of database, which we call a variable database. In addition, since more than one possible interpretation can be given to the specific temporal variables, such as now and ∞, which have appeared in the literature, we discuss several alternative semantics that can be given to these temporal variable databases incorporating one or more of these variables. We also present a constraint on the way such databases are allowed to evolve in time if they are to support a rollback operator.