Re: Distributed foreign keys (was Re: Category Types)
Date: Wed, 2 Jul 2003 19:50:28 +0100
"Bob Badour" <bbadour_at_golden.net> wrote in message
> "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> > To me, the thing that is broken is not (particularly) multiple assignment,
> > view updating. If we did not have view updating, then we could just limit
> > multiple assignment to assigning values to relvars just once, but with
> > updating we have to allow one relvar to be updated twice.
> > The alternative of banning views as targets in multiple assignment smacks
> of a
> > hack, so I just go for banning views as targets of assignments at all :-)
> I don't think that views cause the problem. I think the parallelism is the
In the first edition they did the component parts of multiple assignment 'in sequence'.
I say that if you want a sequence of updates, then nest those updates. If you want them in parallel, then you must statically avoid overlaps. You only get overlaps if you allow view updates.
> Why do you think the constraints are not in the catalog? The predicate of
> the view should appear in the catalog. Is there something I am missing?
Well for one, the fact that the Manifesto admits that "there are known to be certain limitations on the degree to which constraint inference [for virtual relvars] might be feasible in practice".
Business Intelligence, IBM Global Services Received on Wed Jul 02 2003 - 20:50:28 CEST