Re: A pk is *both* a physical and a logical object.
From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 26 Jul 2007 13:33:16 GMT
Message-ID: <wo1qi.7977$fJ5.772_at_pd7urf1no>
>
> permits
>
>
>
> This is the point I have been trying to make for the past week or so. The
> mathematics of the relational data model don't, in this case, disambiguate
> two profoundly different scenarios in the real world the data purports to
> describe.
> ...
Date: Thu, 26 Jul 2007 13:33:16 GMT
Message-ID: <wo1qi.7977$fJ5.772_at_pd7urf1no>
David Cressey wrote:
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:DjPpi.24618$Rw1.11254_at_newssvr25.news.prodigy.net...
>
>
>>This illustrates what happens when the only key on a relation schema
>
> permits
>
>>updates. It can't be determined if a new individual is being selected, or >>if the state of the current individual is now different.
>
>
> This is the point I have been trying to make for the past week or so. The
> mathematics of the relational data model don't, in this case, disambiguate
> two profoundly different scenarios in the real world the data purports to
> describe.
> ...