Databases Reference
In-Depth Information
Row
#
1
oid
eff-beg
eff-end
asr-beg
asr-end
epis-
beg
client
type
copay
row-crt
P861
P861
P861
P861
P861
P861
P861
P861
P861
P861
P861
P861
Feb10
Apr10
Mar12
Jan10
C882
C882
C882
C882
C882
C882
C882
C882
C882
C882
C882
C882
HMO
$15
$20
$20
$15
$20
$20
$20
$40
$40
$40
$40
Feb10
Feb10
2
3
4
5
6
7
8
<9>
<10>
<11>
<12>
Apr10
Apr11
Oct10
Jan12
Jan12
Jan10
HMO
Mar10
Apr10
Jul11
PPO
Apr11
Apr11
Apr11
Apr11
Jul11
9999
HMO
Jul11
May12
Jul11
Jan11
Mar11
Aug11
Jan12
Jan11
HMO
Aug11
Jan10
Mar12
Mar12
Mar12
Feb10
Jan10
PPO
Oct11
Oct11
Apr10
Jul10
Jan12
Jan10
HMO
Jan12
Jan12
Jan12
Jan12
Jul10
Oct10
Jan10
Jan12
HMO
Apr11
Jul11
Jan12
May12
Apr11
PPO
Jan11
Jan11
May11
Mar11
Jan12
May12
HMO
PPO
May11
May12
May12
Jul11
May12
9999
9999
Jul11
9999
May12
May11
HMO
$15
Figure 10.17 Shortening an Episode Forwards: After Step 2.
of a target episode in current assertion time. It withdrew part but
not all of that episode, bringing about the temporal extent trans-
formation in which an episode is {shortened forwards}.
In this way, a temporal delete is different from a non-temporal
delete. Non-temporal deletes remove the one and only row
representing an object from the database. Temporal deletes
remove some but not necessarily all of the possibly multiple rows
representing an object, and may also remove part but not neces-
sarily all of any one (or two) of those rows. And, of course, tempo-
ral deletes do not physically remove any data from the database.
They just withdraw assertions and end the effective time of vers-
ions, so that at any point in time, what used to be the case can
be recreated exactly as it was then.
Shortening an Episode Backwards
A temporal delete can also {shorten an episode backwards} in
time. This happens when the transaction's target range [overlaps]
later clock ticks in the episode (and perhaps additional clock ticks
as well) while one or more earlier clock ticks are not [overlapped].
{Shortening an episode backwards} is easier than {shortening
it forwards} because it doesn't alter the episode's begin date.
Since the episode's begin date remains the same, the only vers-
ions in the episode that are affected by the transaction are those
which [overlap] the transaction's target range. If we're really for-
tunate, the target range will line up on version boundaries. An
example would be a temporal delete whose target range is
[Jul 2011 - 12/31/9999] against the episode still asserted in
Figure 10.17
. In this case, the timespan on this transaction
[equals] the effective time of version 12.
