Databases Reference
In-Depth Information
conclusion of the temporal transaction, immediately becomes a past
date. This is a “clearing the decks” transformation which removes the
representation of the object affected by the transaction from current
assertion time.
A temporal transaction cannot set a row's assertion end date to a past
date because, if it did, it would create a contradiction. During the time
period from that past date to the time the transaction took place, the
database asserted that row. But after Now(), the record of that assertion is
erased from the database. Just as we cannot retroactively begin an
assertion, we cannot retroactively end one, either. This is another
manifestation of the temporalized extension of the Closed World
Assumption.
If a temporal transaction sets a row's assertion end date to a future date, it
locks that row, making it a closed version. Only deferred transactions can
set a row's assertion end date to a future date.
Thus, no temporal transaction can set a row's assertion end date to a past
date. Deferred transactions set that date to a future date. Non-deferred
transactions set that date to Now(), and then as soon as the transaction is
complete, that row is in past assertion time.
Components:
9999, assertion end date, asserted version table, past assertion time.
