The Historical Relational Data Model (Hrdm) and Algebra Based on Lifespans

Critical to the design of an historical database model is the representation of the Atilde;cent;Acirc;not;Acirc;SexistenceAtilde;cent;Acirc;not;Acirc;?of objects across the temporal dimension -- for example, the quot;birth,quot; quot;death,quot; or quot;rebirthquot; ofan individual, or the establishment or dis-establishment of a relationship. The notion of thequot;lifespanquot; of a database object is proposed as a simple framework for expressing these concepts.An object's lifespan is simply those periods of time during which the database models theproperties of that object. In this paper we propose the historical relational data model (HRDM)and algebra that is based upon lifespans and that views the values of all attributes as functionsfrom time points to simple domains. The model that we obtain is a consistent extension of therelational data model, and provides a simple mechanism for providing both time-varying dataand time-varying schemes