A database fact is stored in a database at some point in time, and after it is stored, it is current until logically deleted. The transaction time of a database fact is the time when the fact is current in the database and may be retrieved. Transaction times are consistent with the serialization order of the transactions. Transaction-time values cannot be later than the current transaction time. Also, as it is impossible to change the past, transaction times cannot be changed. Transaction times may be implemented using transaction commit times, and are system-generated and -supplied.