Databases Reference
In-Depth Information
valid time
Description:
the computer science term “valid time” may be treated as
co-extensive with our term “effective time”.
Comments:
“The valid time of a fact is the time when the fact is true in the modeled
reality. A fact may have associated any number of events and intervals, with
single events and intervals being important special cases.” From [Jensen,
1992].
version
Mechanics:
a row in an asserted version table which makes a statement about
whattheobjectitrepresentsislike during a specified effective time
period.
Semantics:
a row in a table which represents the state of an object during a
specified period of time.
Comments:
Every row in an asserted version table is either a past, present or future
version representing an object.
Components:
asserted version table, effective time period, object, represent,
statement.
version begin date
Description:
the date on which a row in a best practices version table begins.
Comments:
This expression does
not
apply to a row in an asserted version table. A
row in an asserted version table is a version, and the begin date associated
with that row, as a version, is its effective begin date. The version begin
date of a row in any other kind of version table might represent either the
physical date on which the row was created, or a logical date on which
the version becomes effective.
version end date
Description:
the date on which a row in a best practices version table ends.
Comments:
This expression does
not
apply to a row in an asserted version table.
A row in an asserted version table is a version, and the end date
associated with that row, as a version, is its effective end date. The
version end date of a row in any other kind of version table might
represent either the physical date on which a delete transaction was
applied to the row, or a logical date on which the version ceased to be
in effect.
version split
Mechanics:
a process in which the representation of an object is removed from
one or more effective-time clock ticks that [fill] the effective time period of a
version.
Semantics:
a process in which one version is withdrawn, and replaced by two
versions.
Comments:
When a version is split, the earlier half becomes a new version which is
located [before] the latter half. Because the two versions are not
contiguous, the result of splitting a version is always to split an episode.
See also:
temporal extent state transformation {split}
.
