Temporal Logic in Database Query Languages

DEFINITION The term “temporal logic” is used, in the area of formal logic, to describe systems for representing and reasoning about propositions and predicates whose truth depends on time. These systems are developed around a set of temporal connectives, such as sometime in the future or until, that provide implicit references to time instants. First-order temporal logic is a variant of temporal logic that allows first-order predicate (relational) symbols, variables and quantifiers, in addition to temporal connectives. This logic can be used as a natural temporal query language for point-stamped temporal databases. A query (a temporal logic formula) is evaluated with respect to an evaluation point (time instant). Each such point determines a specific database snapshot that can be viewed as a relational database. Thus, the evaluation of temporal logic queries resembles the evaluation of first-order (relational calculus) queries equipped with an additional capability to “move” the evaluation point using temporal connectives. In this way, it becomes possible to refer in a single query to multiple snapshots of a given temporal database. The answer to a temporal logic query evaluated with respect to all time instants forms a point-stamped temporal relation.