Re: more on delete from join

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 02 Sep 2009 13:07:53 -0300
Message-ID: <4a9e9864$0$23750$9a566e8b_at_news.aliant.net>



paul c wrote:

> Marshall wrote:
>

>> On Sep 2, 2:44 am, "Joe Thurbon" <use..._at_thurbon.com> wrote:
>>
>>> 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.
>> ...

>
> We know "a implied b" because we chose to record it. We could choose to
> record same for a so-called "base relation", so how are they different?
> Even "base" updates must deal with constraints. As far as a database
> is concerned, If there is a difference, it is that the recording of one
> value is physically optimized compared to the other, ie., the
> difference is physical, not logical.

Even then, the ability to store data in ways that differ significantly from one's base relations is highly desired. (Physical independence) Received on Wed Sep 02 2009 - 11:07:53 CDT

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