Transaction time (TT), a concept originated by Richard T. Snodgrass and his doctoral student, is used in temporal databases. It denotes the time period during which a database fact is/was stored in the database. As of December 2011, ISO/IEC 9075, Database Language SQL:2011 Part 2: SQL/Foundation included clauses in table definitions to define "system-versioned tables" (that is, transaction-time tables).
In a database table transaction time is often represented by two extra table-columns StartTT and EndTT. The time interval is closed at its lower bound and open at its upper bound.
When the ending transaction time is unknown, it may be considered as "Until Closed". Academic researchers and some RDBMS have represented "Until Closed" with the largest timestamp supported or the keyword "forever". This convention is not technically precise.
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