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Paul Vernon <paul.vernon_at_ukk.ibmm.comm> wrote in message news:<ancq69$t0k$2_at_sp15at20.hursley.ibm.com>...
> Out of interest, how does D4 insert into this view?
>
> (A UNION B) MINUS (A INTERSECT B)
>
> It seems to me to be entirely arbitrary to insert into A rather than B, or
> vis-versa, and only slightly less arbitrary to not allow any inserts at
> all.
I would suggest an analogy between your equation
V = (A UNION B) MINUS (A INTERSECT B) and algebraic equation
Z = X + Y
In the second case if we know Z, we cant solve it unambiguously for X and Y values. In order to resolve ambiguity, we have to add a second equation.
Likewise, if we add a second view
W = A minus B
then the view set {V,W} is perfectly updateable.
For example, if we see a transaction
insert 1 into V;
insert 1 into W;
commit;
then it's definetely an insert into A. On the other hand,
insert 1 into V;
commit;
is certainly an insert into B. Received on Fri Oct 04 2002 - 17:21:33 CDT