Databases Reference
In-Depth Information
Semantics:
the date indicating when an effective time period ends.
Comments:
The effective end date of an episode is the effective end date of its latest
version.
Components:
closed-open, effective time period.
effective time
Mechanics:
the temporal dimension along which effective time periods are
located.
Semantics:
the temporal dimension which interprets a time period on a row as
indicating when the object represented by that row existed such that the row
was the unique row validly representing that object.
Comments:
We do
not
say “The temporal dimension which interprets a time period
on a row as indicating when that row was the unique row validly
representing that object” because that suggests that this temporal
dimension is a property of rows. It is not. It is a property of objects
represented by rows.
But assertion time periods
are
properties of rows or, more precisely, of the
existentially quantified statements made by those rows.
Components:
temporal dimension, effective time period, object, represent.
effective time period
Mechanics:
the period of time of a version or an episode starting on its effective
begin date and ending one clock tick prior to its effective end date.
Semantics:
the period of time during which an object exists, as asserted by a row
in an asserted version table.
Components:
assert, asserted version table, clock tick, effective begin date,
effective end date, episode, object, time period, version.
effective time versioning
Mechanics:
a form of versioning similar to temporal gap versioning, but in which
a row create date is added to each version, in addition to a version begin date
and a version end date.
Semantics:
a form of versioning in which versions of the same object may or may
not be contiguous, in which no version is physically deleted, in which the
version dates delimit an effective time period, and in which the date the row
was physically created is also provided.
Comments:
Effective time versioning is not part of Asserted Versioning. See
Chapter 4.
See also:
basic versioning, logical delete versioning, temporal gap
versioning
.
Components:
contiguous, effective time period, object, row create date, temporal
gap versioning, version, version begin date, version end date.
empty assertion time
Mechanics:
an assertion time period whose begin and end dates have the same
value.
Semantics:
an assertion time period which includes no clock ticks.
Comments:
Deferred assertions which are deleted before they become currently
asserted are moved into empty assertion time, i.e. are given empty
assertion time periods.
