Re: more on delete from join

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 02 Sep 2009 16:59:05 -0300
Message-ID: <4a9ece94$0$23744$9a566e8b_at_news.aliant.net>



paul c wrote:

> Bob Badour wrote:
>

>> 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)

>
> Exactly. People who want to treat views differently should play tthe
> ball where it lies and admit that a named view is a physical
> optimization device (which has been confusing people for many years
> now).

That may be how people use views now--I neither know nor have an opinion--however, a view is a logical device not a physical device. One uses views for logical independence not physical optimization. Received on Wed Sep 02 2009 - 14:59:05 CDT

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