Databases Reference
In-Depth Information
This is important to know when creating indexes for perfor-
mance, as described in Chapter 15.
Any report about the effective-time past can be either an
as-was or an as-is report. If it is an as-is report, it can be
produced from Current History. But if it is an as-was report, it
can be produced only from Posted History.
Posted Updates: Past Claims About the Present
The Posted Updates dataset consists of all those rows in an
asserted version table which lie in the assertion time past but
in the effective time present. Its subject matter is things as they
currently are. Its rows are claims about these things which we
are no longer willing to make. Posted Updates are a record of
all the times we got it wrong about what is now the present, up
to but not including our current claims about that present.
Those current claims, of course, are the ones in which we finally,
we hope, got it right.
Here is the view which re-presents Posted Updates. With
the suffix “Post_Upd” standing for “posted updates”, it looks
like this:
CREATE VIEW V_Policy_Post_Upd
AS SELECT oid, asr_beg_dt, asr_end_dt, eff_beg_dt, eff_end_dt,
client, type, copay
FROM Policy_AV
WHERE asr_end_dt
<¼
Now()
AND eff_beg_dt
<¼
Now() AND eff_end_dt
>
Now()
The Posted Updates dataset is also a bi-temporal collection
of data, and so both time periods must be included on all
rows in the view. The unique identifier for this or for any other
bi-temporal view of an asserted version table, is the combination
of oid, any one or both of the assertion dates, and any one or
both of the effective dates.
what we used to claim
what we currently claim
what we will claim
what things
used to be like
what things
are like
what things
will be like
what we used to claim
things are like now
Figure 13.5 Posted Updates.
