Databases Reference
In-Depth Information
Temporal Delete
Physical Transaction(s)
Remove an object
from a designated
timespan.
Withdraw the affected versions.
Assert the replacements which
delimit the deletion.
Reset affected versions.
Figure 10.13 The Temporal Delete Transaction: Temporal to Physical Mapping.
A temporal delete is the inverse of a temporal insert. A tem-
poral insert always increases the total number of clock ticks
occupied by an object. A temporal delete always decreases the
total number of those clock ticks.
As long as even a single clock tick in the transaction's target
timespan [
intersects
] the effective time period of some version
of the same object, the delete is valid because it means that there
is data in one or more clock ticks for the delete to move into past
assertion time.
A temporal delete's target range may include part of an epi-
sode or version, an entire episode or version, multiple episodes
or versions, or any combination thereof. But a temporal delete
never creates a new episode or version in clock ticks that were
previously unoccupied, just as a temporal insert never removes
one from clock ticks that were previously occupied.
Deleting One or More Episodes
We will begin with the set of three episodes shown in
Figure 10.14
. These are the current episodes A, B and C after being
updated as shown in
Figure 10.12
. We have also reset the version
numbers so they correspond to the row numbers in
Figure 10.12
.
To completely remove an episode from current assertion
time, we do not need to provide the exact begin and end dates
of the episode, but simply need to include its effective time
Episode A
Episode C
Episode B
6
1
7
8
10
9
4
Jan
2010
Jan
2011
Jan
2012
Jan
2013
Jan
2014
Figure 10.14 Deleting an Episode: Before the Transaction.
