Re: Universal Quantifier
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 27 Jan 2007 16:01:07 GMT
Message-ID: <7HKuh.5831$1x.100757_at_ursa-nb00s0.nbnet.nb.ca>
>
> Regarding irreducibility, do we not express it by our choice of p1 and
> p2? Ie., what we express with a reducible p1 is extraneous?
Date: Sat, 27 Jan 2007 16:01:07 GMT
Message-ID: <7HKuh.5831$1x.100757_at_ursa-nb00s0.nbnet.nb.ca>
>> ... >> >>> What formula would express a primary key? >> >> Faking it heavily, I suggest something along the lines of: >> >> forall A1(p1,q1) in A(p,q). forall A2(p2,q2) in A(p,q). >> if p1 = p2 then q1 = q2; >> >> where p is actually the set of attributes composing the key and q is >> actually the set of dependent attributes. >> >> One also has to express irreducibility, though.
>
> Regarding irreducibility, do we not express it by our choice of p1 and
> p2? Ie., what we express with a reducible p1 is extraneous?