Re: The wonderful world of keys
From: Joe Thurbon <usenet_at_thurbon.com>
Date: Thu, 25 Jan 2007 03:05:01 GMT
Message-ID: <x7Vth.51$5W.25_at_news-server.bigpond.net.au>
>
> I would have thought '~a v true' was equivalent to 'true'?
Date: Thu, 25 Jan 2007 03:05:01 GMT
Message-ID: <x7Vth.51$5W.25_at_news-server.bigpond.net.au>
JOG wrote:
>
> On Jan 24, 9:15 pm, Joe Thurbon <use..._at_thurbon.com> wrote:
>> On 2007-01-25 02:59:58 +1000, "JOG" <j..._at_cs.nott.ac.uk> said: >> >> >> ~a v true >> >> which is equivalent to >> >> ~a.
>
> I would have thought '~a v true' was equivalent to 'true'?
D'oh. Of course, you are right. I should know better than to post before breakfast.
[...]
>
> Perhaps traditional db thinking is back to front; perhaps if a
> proposition has no material implication instead of a full-superkey it
> /has no key at all/ - it is an unnecessary concept for such a relation,
> given the fact that if I attempted to duplicate this 'key' then I would
> be duplicating the whole tuple, which is already forbidden given the
> tuple is a set element. But then perhaps I just drink too much coffee.
>
It's possible. At least you didn't mix up conjunction and disjunction.
<blush>
Joe Received on Thu Jan 25 2007 - 04:05:01 CET