Re: constraints in algebra instead of calculus
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 24 May 2007 00:17:50 -0300
Message-ID: <46550391$0$4021$9a566e8b_at_news.aliant.net>
>
> I would think restriction and difference can be distributed naively as
> above. If nobody else here formulates the other two, I'll be getting
> around to it in the next few months for other reasons.
Date: Thu, 24 May 2007 00:17:50 -0300
Message-ID: <46550391$0$4021$9a566e8b_at_news.aliant.net>
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message >> >>> ... >>> If view V = A & B, surely constraint C on the view, giving V & C, >>> would be manipulated by an engine with the same effect as the >>> expression (A & C) & (B & C). >>> >>> I've never heard of anybody requiring expressions to result in BCNF >>> values, surely that would cripple an algebra. >> >> They don't. Nor should they. But an expression defining a view can >> involve anything, restriction, difference, aggregation, division. How >> does a constraint on the view map to constraints on the base tables?
>
> I would think restriction and difference can be distributed naively as
> above. If nobody else here formulates the other two, I'll be getting
> around to it in the next few months for other reasons.
I don't know why you indulge him. Constraints are simply wffs. One can map a view constraint to the base relations by simple substitution. Received on Thu May 24 2007 - 05:17:50 CEST