Databases Reference
In-Depth Information
closed episode
Mechanics:
an episode whose effective end date is not 9999.
Semantics:
an episode whose effective end date is known.
Components:
9999, effective end date, episode.
closed-closed
Mechanics:
a convention for using a pair of clock ticks to designate an effective or
assertion time period, in which the earlier clock tick is the first clock tick in
the time period, and in which the later clock tick is the last clock tick in the
time period.
Comments:
Using this convention, two time periods [meet] if and only if the
begin date of the later one is one clock tick after the end date of the
earlier one, at whatever level of granularity is used to designate the
clock ticks.
Components:
assertion time period, clock tick, effective time period.
closed-open
Mechanics:
a convention for using a pair of clock ticks to designate an effective
or assertion time period, in which the earlier clock tick is the first clock tick
in the time period, and in which the later clock tick is the first clock tick after
the last clock tick in the time period.
Comments:
Using this convention, two time periods [meet] if and only if the
begin date of the later one is the same clock tick as the end date of the
earlier one, at whatever level of granularity is used to designate the
clock ticks.
Components:
assertion time period, clock tick, effective time period.
contiguous
Mechanics:
time period or point in time X is contiguous with time period or point
in time Y if and only if either X [meets] Y or X [meets
1
]Y.
Components:
Allen relationship [meets], Allen relationship [meets
1
], point in
time, time period.
conventional data
Mechanics:
data in a conventional table.
Semantics:
data which represents currently asserted current versions of
persistent objects, but which lacks assertion time periods and effective time
periods.
Comments:
More accurately, conventional data is data which lacks
explicitly
expressed
assertion and effective time periods. For in fact,
conventional data is asserted, and its assertion time period is
co-extensive with its physical presence in the database. And
conventional data is also versioned, and the effective time of the one
version of an object thus represented is always from Now() until further
notice.
Components:
assertion time period, conventional table, currently asserted current
version, effective time period, persistent object.
conventional database
Mechanics:
a database none of whose tables are temporal.
