Databases Reference
In-Depth Information
Comments:
That current assertion time starts Now(), i.e. when the transaction is
processed, and continues on until further notice. Every temporal
transaction that accepts the default values for effective time, creates a
version that describes what its object looks like
from now on
. Every
non-deferred temporal transaction creates an assertion that,
from now
on
, claims that its version makes a true statement. (From Chapter 9.)
Components:
9999, clock tick, Now(), time period, until further notice.
f
TRI function
Mechanics:
a function that evaluates to True if and only if a valid TRI relationship holds
between the episode and the version specified in the function.
Components:
episode, TRI, version.
future assertion
See
deferred assertion
.
future version
Mechanics:
a row in an asserted version table whose effective begin date is later
than Now().
Semantics:
a row in an asserted version table which describes what the object
it represents will be like during a specified future period of time.
Components:
asserted version table, effective begin date, Now(), object, represent,
time period.
granularity
Mechanics:
the size of the unit of time used to delineate effective time periods
and assertion time periods in an asserted version table.
Comments:
More generally, the granularity of a measurement is the size of the units
in which the measurement is expressed, a smaller size referred to as a
“finer” granularity. For example, inches are a finer granularity of linear
measurement than yards, and ounces are a finer granularity of the
measurement of weight than pounds.
Components:
asserted version table, assertion time period, effective time period.
hand-over clock tick
Semantics:
the point in near future assertion time to which an approval
transaction sets the assertion begin date of one or more deferred assertions,
and also the assertion end date of any assertions which were locked as a
result of creating them.
Components:
approval transaction, assertion begin date, assertion end date,
deferred assertion, lock, near future assertion time, replace, supercede.
historical data
Mechanics:
rows in asserted version tables whose effective end date is earlier than
Now().
Semantics:
data which describes the past state or states of a persistent object.
Comments:
Note that this term does not refer to data which is itself, historical, i.e. to
no longer currently asserted data, but rather to data which is about
history, i.e. about the past states of persistent objects.
For the term which does refer to data which is itself historical, see also
as-was data
.
