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Re: No exceptions?

From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 30 Jun 2006 05:49:59 GMT
Message-ID: <bY2pg.109995$Mn5.101623@pd7tw3no>


J M Davitt wrote:

>...

> All the attributes in a relation comprise, at least, a superkey. The
> set of attributes that qualify as a candidate key must hold unique
> values and no subset of those attributes must hold unique values. The
> only relations that could have empty candidate keys are those with
> empty headings, right?

Apologies - I'll try to read the rest tomorrow, but right now I'm tired (from watching a library video - "Guns, Germs and Steel" - the author seems to be the James Burke of biology, not that I know much about the latter). I thought a relation with any number of attributes could have only one value for them if it had an 'empty' set of candidate keys, eg. a relation that has only one tuple? (and a 'relvar' could have only one value at any instant in time)?

p Received on Fri Jun 30 2006 - 00:49:59 CDT

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