Re: Possible problems with Date & McGoveran View Updating
Date: 17 Sep 2003 07:25:20 -0700
Message-ID: <e4330f45.0309170625.2180db5b_at_posting.google.com>
"Bob Badour" <bbadour_at_golden.net> wrote in message news:<lGx7b.822$D23.74785835_at_mantis.golden.net>...
> > The common sense principle of prudence (don't make assumptions without
> > enough information), has more priority than the principles of beauty
> > :-)
>
> This boils down to the closed world assumption, which is widely accepted in
> database management.
No, I don't see the relation. The closed world assumption is a user assumption. The DBMS must manage the declared facts according to the principles of logic.
(A or B) is true
A may be true
B can not be true (is false)
A is true -- Correct
(A or B) is true
A may be true
B may be true
(A and B) is true -- Great blunder!! (although very symmetrical :)
> > I agree with Mikito here. Any decision is an arbitrary assumption. You
> > are stating as true, things you can't know if they are really true.
>
> Yes, the dbms can know. If they can not be true, the dba can declare a
> constraint that resolves the issue one way or the other.
Agreed, but my point is that if the dba does not declare the constraint the update must be rejected for safety.
> I agree that POOD does not suffice to prevent the issue -- at least, as far
> as I understand POOD. POOD applies to all relvars;
To all base relvars.
"Within a given database, no two distinct base tables shouldhave overlapping meanings."
http://www.pgro.uk7.net/orthog_2_1110.htm
> relvars has a unique predicate. I think you are persuading me to your point
> of view, but I wonder whether some other design principle might resolve the
> issue.
Yes, but I am talking only about the DBMS inference rules. The DBMS deductions must be logically correct even with incompetent but legal database designs.
> I would suggest in this case that it was unwise of the dba to grant update
> rights to this relvar given the problem you identify.
Agreed, but it is not an excuse for wrong deductions.
> > And if we find a better way changing the rules, why don't use it?
>
> I wonder whether this is something a dba can resolve under the covers by
> specifying whether to insert to both or to reject the update as ambiguous.
Yes, the dba may workaround the DBMS flaws, but I prefer a DBMS without flaws.
Regards
Alfredo
Received on Wed Sep 17 2003 - 16:25:20 CEST