Databases Reference
In-Depth Information
existence dependent on the object for that episode in Y, and the effective time
period of that episode in Y [fills
1
]the effective time period of that version in X.
Components:
Allen relationship [fills
1
], asserted version table, effective time
period, episode, existence dependency, object, object identifier, temporal
foreign key, version.
chronon
Semantics:
the term used in the computer science community for what Asserted
Versioning calls an atomic clock tick.
Comments:
See the 1992 entry in the bibliography for the standard computer science
glossary of bi-temporal concepts.
Components:
atomic clock tick.
circa flag
Mechanics:
a flag used by the Asserted Versioning Framework as a component of
one or more indexes on asserted version tables, in order to improve the
performance of queries which reference asserted version tables, and also of
updates to those tables.
Semantics:
a flag which distinguishes between rows which are definitely known to
be in the assertion time past from all other rows. (See Chapter 15).
Components:
Asserted Versioning Framework, asserted version table, assertion time.
clock tick
Mechanics:
the unit of time used for effective begin and end dates, assertion
begin and end dates, episode begin dates and row create dates, in an asserted
version table.
Semantics:
the transition from one point in effective time or assertion time to the
next point in effective time or assertion time, according to the chosen
granularity which defines those two points in time as contiguous.
Comments:
Note that chronons are atomic clock ticks, not clock ticks.
A 1-month-per-tick clock represents a situation in which a database is
updated at most once a month. By the same token, a 1-week or 1-day
clock would record updates that take place at most once a week or once
daily, respectively.
Components:
asserted version table, assertion begin date, assertion end date,
contiguous, effective begin date, effective end date, granularity, episode begin
date, point in time, row create date.
closed assertion
Mechanics:
a row in an asserted version table whose assertion end date is not 9999.
Semantics:
a row in an asserted version table with a known assertion end date.
Components:
asserted version table, assertion end date, 9999.
closed assertion time
Mechanics:
an assertion time period whose end date is not 9999.
Semantics:
an assertion time period whose end date is known.
Components:
9999, assertion end date, assertion time period.
closed effective time
Mechanics:
an effective time period whose end date is not 9999.
Semantics:
an effective time period whose end date is known.
Components:
9999, effective end date, effective time period.
