Re: more on delete from join
Date: Wed, 02 Sep 2009 15:31:57 GMT
>> 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. Received on Wed Sep 02 2009 - 17:31:57 CEST