Databases Reference
In-Depth Information
temporal tag
Description:
a metaphor for the association of a row of data with a time period.
The time period is a temporal tag applied to the row.
temporal transaction
Mechanics:
an insert, update or delete transaction whose target is an asserted
version table.
Semantics:
an insertion, update or deletion of a temporally delimited assertion of
a statement describing an object as it exists during a specified period of
effective time.
Components:
asserted version table, assertion, effective time period, object,
statement, target table.
temporal update
Mechanics:
a temporal transaction against an asserted version table which
modifies business data representing an object in one or more contiguous or
non-contiguous effective-time clock ticks.
Semantics:
a temporal transaction against an asserted version table which
changes one or more business data items describing that object in one or
more clock ticks included in the transaction's specified period of effective
time.
Comments:
Note that a temporal update will change the business data for an object
in occupied clock ticks, and will ignore unoccupied clock ticks. Thus the
clock ticks that a temporal update affects are not necessarily contiguous
clock ticks. And consequently, to be valid, it is not necessary that all clock
ticks in the effective-time range of a temporal update be occupied by the
specified object. It is only necessary that at least one of them be
occupied.
Components:
asserted version table, business data, clock tick, contiguous,
effective time period, object, represent, temporal transaction.
temporalize
Mechanics:
to temporalize a managed object is to associate an explicit assertion
time period and/or an explicit effective time period with it.
Components:
assertion time period, effective time period, managed object.
temporalized extension of the Closed World Assumption
Mechanics:
the constraint that a temporal transaction cannot insert data into past
assertion time, update data in past assertion time, or delete data from past
assertion time.
Semantics:
the assumption that if a statement was not represented in the
database at time T
1
, then at time T
1
we did not make that statement.
Comments:
Note, by contrast, that a temporal transaction can insert data into past
effective time, update data in past effective time, and delete data from
past effective time.
In Chapter 12, we explained the reason that we can modify the statement
content of past effective time but not of past assertion time. We said: “. . .
. . a belief is expressed by the presence of a row in a table. No row, no
belief. So if we write a transaction today that creates a row stating that we
believed something yesterday, we are creating a row that states that we
believed something at a time when there was no row to represent that
