Databases Reference
In-Depth Information
(eff_end_dt
1
>
eff_end_dt
2
).
Semantics:
P
1
[overlaps
1
]P
2
if and only if the first clock tick in P
1
is later than the
first clock tick in P
2
, and the first clock tick in P
1
is earlier than the next
clock tick after the end of P
2
, and the last clock tick in P
1
is later than the last
clocktickinP
2
.
Allen relationship, [starts]
Mechanics:
P
1
[starts] P
2
if and only if (eff_beg_dt
1
¼
eff_beg_dt
2
) AND
(eff_end_dt
1
<
eff_end_dt
2
).
Semantics:
P
1
[starts] P
2
if and only if the two time periods start on the same clock
tick, and the last clock tick in P
1
is earlier than the last clock tick in P
2
.
Allen relationship, [starts
1
]
Mechanics:
P
1
[starts
1
]P
2
if and only if (eff_beg_dt
1
¼
eff_beg_dt
2
) AND
(eff_end_dt
1
>
eff_end_dt
2
).
Semantics:
P
1
[starts
1
]P
2
if and only if the two time periods start on the same
clock tick, and the last clock tick in P
1
is later than the last clock tick in P
2
.
Allen relationships
Mechanics:
the set of 13 positional relationships between two time periods, a time
period and a point in time, or two points in time, as first defined in James F.
Allen's 1983 article
Maintaining Knowledge about Temporal Intervals
.
Semantics:
the set of all possible positional relationships between two time
periods, a time period and a point in time, or two points in time, defined
along a common timeline.
Comments:
The Allen relationships are mutually exclusive and jointly exhaustive.
Good discussions of the Allen relationships can also be found in
(Snodgrass, 2000), from Chapter 4, and (Date, Darwen and Lorentzos,
2002), from Chapter 6.
Components:
time period, point in time.
approval transaction
Mechanics:
a transaction that changes the assertion begin date on the assertions
in a deferred assertion group to an earlier date.
Semantics:
a transaction that moves assertions in an deferred assertion group
from far future assertion time to near future assertion time.
Comments:
The transaction by which deferred assertions are moved close enough to
Now() that the business is willing to let them become current by means of
the passage of time. See also:
fall into currency
.
Components:
assertion, assertion begin date, deferred assertion group, far future
assertion time, near future assertion time.
as-is
Mechanics:
data whose assertion begin date is earlier than Now() and whose
assertion end date is later than Now().
Semantics:
data whose assertion time period is current.
Comments:
See also:
as-was
. The as-is vs. as-was distinction is often confused with
the distinction between current and past versions. Many best practices
implementations of versioning do not distinguish between the two, and
therefore introduce ambiguities into their temporal semantics.
Components:
assertion begin date, assertion end date, assertion time period, Now().
