Re: insert to projection

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 05 Sep 2009 02:57:30 GMT
Message-ID: <uskom.43824$PH1.21867_at_edtnps82>



Mr. Scott wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
> news:DGbom.42669$Db2.5159_at_edtnps83...
>> Why do implementation languages not allow this?  Surely not for logical 
>> reasons?  We can delete from projection because NOT Pa implies NOT Pab, 
>> eg., <NOT> R{a} -> <NOT> R{a,b}.  Logically, we can insert to projections 
>> because Pab implies Pa.  Isn't the problem really a language deficiency?

>
> I don't understand. Is the binary predicate P somehow related to the unary
> predicate P, and if so, how exactly?
>
>
>

Sure it is, the truth of the tuple <a 1, b 2> implies the truth of the tuple <a 1> and the falsity of the tuple <a 1> implies the falsity of <a 1, b 2>, as far as a relation R with predicate P is concerned. Projection means quantification and vice versa, what's the problem? (Could it be that predicates aren't recorded?). Received on Fri Sep 04 2009 - 21:57:30 CDT

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