Re: more on delete from join

From: Walter Mitty <>
Date: Wed, 02 Sep 2009 18:26:46 GMT
Message-ID: <GNynm.863$>

"Marshall" <> wrote in message On Sep 2, 2:44 am, "Joe Thurbon" <> 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.

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.

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

BTW, when I was young they used to call this "converse reasoning". Received on Wed Sep 02 2009 - 20:26:46 CEST

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