Entities and Relations for Historical Relational Databases

Research to extend models of data to handle the temporal dimension has been conducted mainly in the context of the rela-tional data model. In the relational model, the primary object of database design, manipulation and retrieval is the relation, viewed extensionally as a nite set of tu-ples. A formal system for temporal re-lational data deenition and manipulation associates a temporal domain, either intervals or moments (points) of time, with either tuples or attribute values in a relation. This association provides the foundation for the construction of temporal entities , the primary objects of declaration and manipulation. This paper proposes three useful types of temporal entities: events, histories, and valid-time relations, and de-nes relations and operations which allow for patterns of ordering and duration information to be deened and extracted. These patterns can often be expressed as select conditions on temporal relations in an algebraic query language This paper is both a survey of existing trends in temporal database research, and a reenement of the conceptual framework used to characterize temporal information.