Re: more on delete from join

From: Joe Thurbon <usenet_at_thurbon.com>
Date: Wed, 02 Sep 2009 22:51:30 GMT
Message-ID: <op.uzni35m1q7k8pw_at_imac.local>



On Thu, 03 Sep 2009 04:26:46 +1000, Walter Mitty <wamitty_at_verizon.net> wrote:

>
> "Marshall" <marshall.spight_at_gmail.com> wrote in message
> news:badf422a-cd2b-40f1-869b-c0a248363088_at_u36g2000prn.googlegroups.com...
> On Sep 2, 2:44 am, "Joe Thurbon" <use..._at_thurbon.com> wrote:
> <quote:>
>
>>
>> So, to update a view, rather than update the conclusion directly, one
>> must
>> update (one of) the base relvars that are used to derive the
>> conclusion/view. That is abductive.
>
> I guess I see what you mean, but strictly speaking it doesn't seem
> to fit the definition. In abductive reasoning, one knows a -> b, and
> b, but one doesn't know that it was in fact a that implied b. Whereas
> with a view, we do know.
> </quote:>
>
> I think I see what joe is saying, perhaps by analogy. When we give an
> imperative to update a view or assign an after update state to a view,
> it
> is like knowing the conclusion (b). The rule that defines the view is
> like
> knowing the implication (a -> b). And what has to be derived (by the
> DBMS)
> is the update required to the base relvars in order to adhere to both the
> rule in the view definition and the conclusion we have supplied. That's
> like abducting a from b and a -> b.
>

Yep, that's what I was trying to say - thanks for putting it more clearly.

> This might be only an anlogy, or it might be more than an analogy. I'm
> not
> sure.

I had intended it only as an analogy.

There may be a formal relationship, of course, but I won't pretend that I have figured one out.

Cheers,
Joe Received on Wed Sep 02 2009 - 17:51:30 CDT

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