Re: Distributed foreign keys (was Re: Category Types)

From: Paul Vernon <paul.vernon_at_ukk.ibmm.comm>
Date: Wed, 2 Jul 2003 19:50:28 +0100
Message-ID: <be0rgk$1mkg$>

"Bob Badour" <> wrote in message news:LgoKa.528$
> "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> news:bdcm8b$cvm$
> > To me, the thing that is broken is not (particularly) multiple assignment,
> but
> > 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
> view
> > 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
> problem.

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".

Paul Vernon
Business Intelligence, IBM Global Services Received on Wed Jul 02 2003 - 20:50:28 CEST

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