Time In Databases While most databases tend to model reality at a point in time (at the "current"time),temporal databases model the states of the real world across time. Facts in temporal relations have associated times when they are valid, which can be represented as a union of intervals. The transaction time for a fact is the time interval during which the fact is current within the database system. In a temporal relation,each tuple has an associated time when it is true; the time may be either valid time or transaction time. A bi-temporal relation stores both valid and transaction time. Database System Concepts-6th Edition 25.3 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 25.3 ©Silberschatz, Korth and Sudarshan th Edition Time In Databases While most databases tend to model reality at a point in time (at the “current” time), temporal databases model the states of the real world across time. Facts in temporal relations have associated times when they are valid, which can be represented as a union of intervals. The transaction time for a fact is the time interval during which the fact is current within the database system. In a temporal relation, each tuple has an associated time when it is true; the time may be either valid time or transaction time. A bi-temporal relation stores both valid and transaction time