Hypothetical Temporal Reasoning in Databases

Abstract

In this paper we integrate a history–encoding based methodology for checking dynamic database integrity constraints into a situation-calculus based specification of relational database updates. By doing this, we are able to: (1) Answer queries about a whole hypothetical evolution of a database, without having to update the entire database and keep all the information associated to the generated states, (2) State and prove dynamic integrity constraints as static integrity constraints, (3). Transform history dependent preconditions for updates into local preconditions. The methodology presented here is based on the introduction of operators of predicate past temporal logic as macros into the specifications, written in the situation calculus, of the dynamics of a database. Temporal subformulas of a query are treated as auxiliary views with the corresponding specification of their dynamics. An implementation of hypothetical temporal query answering is presented.