Databases Reference
In-Depth Information
include temporal foreign keys, not the column or columns that
were the foreign keys in the original table.
So we do not yet have a view which re-presents the original
conventional table. The Current Data dataset is row-to-row
equivalent to the original table in terms of its contents, but not
in terms of its schema. We do not yet have a view to which all
queries against the original table can be redirected. That view
must replace the oid in Policy_CACV with the original primary
key, and replace the TFK with the original foreign key. And it
must have the same name as the original table. Here is that view:
CREATE VIEW Policy
AS SELECT policy_nbr AS P.policy_nbr, policy_type AS P.
policy_type,
copay_amt AS P.copay_amt, client_nbr AS C.client_nbr
FROM Policy_CACV P
JOIN Client C
ON C.client_oid
ΒΌ
P.client_oid
The most frequently used view of any asserted version table
is likely to be this current data view. These are precisely those
rows that make up the complete contents of a conventional
non-temporal table.
Current Projections: Current Claims About the
Future
The Current Projections dataset consists of all those rows in
an asserted version table which lie in the assertion time present
but in the effective time future. Its subject matter is things as
they may turn out to be. Its rows are claims about these things
which we currently make. Current Projections are a record of
what we currently believe things are going to be like; and, of
course, we shouldn't make such claims unless we are pretty sure
that's how they will turn out to be. If we aren't pretty sure about
them, then we should make them, if we make them at all, as
pending projections.
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 currently claim
things will be like
Figure 13.9 Current Projections.
