Databases Reference
In-Depth Information
oid
P861
eff-beg
eff-end
client
type
copay
Jan10
Jul10
C882
HMO
$15
Figure 9.2 A Uni-Temporal Version.
July 2010, has a client of C882, a type of HMO and a copay of
$15.” In other words, the row shown in
Figure 9.2
has been
placed in a temporal
container
, and is treated as representing
the object as it exists within that container, but as saying nothing
about the object as it may exist outside that container.
If we were managing uni-temporal versioned data, that would
be the end of the story. But if we are managing bi-temporal data,
there is one more temporal tag to add. This same row, with an
assertion time period attached, is shown in
Figure 9.3
.
It makes the following statement: “I represent the assertion,
made on January 2010 but withdrawn on October 2010, that
this row represents a policy which has an object identifier of
P861 and which, from January 2010 to July 2010, has a client
of C882, a type of HMO and a copay of $15.” In other words,
the row shown in
Figure 9.2
, as included in its first temporal
container, has been placed in a second temporal container,
and is treated as representing what we claim, within that sec-
ond container, is true of the object as it exists within that first
container, but as saying nothing about what we might claim
about the object within its first container outside that second
container.
From January to July, this statement makes a current claim
about what P861 is like during that period of time. From July
to October, this statement makes an historical claim, a claim
about what P861
was
like at that time. But from October on, this
statement makes no claim at all, not even an historical one. It is
simply a record of what we once claimed was true, but no longer
claim is true.
All this is another way of saying (i) that a non-temporal row
represents an object; (ii) that when that row is tagged with an
effective time period, it represents that object as it exists during
that period of time (January to July in our example); and (iii) that
when that tagged row receives an additional time period tag, it
represents our assertion, during the indicated period of time
oid
P861
eff-beg
eff-end
asr-beg
asr-end
Oct10
client
type
HMO
copay
C882
$15
Jan10
Jul10
Jan10
Figure 9.3 A Bi-Temporal Row.
