Re: foreign key constraint versus referential integrity constraint
Date: Thu, 29 Oct 2009 00:18:59 -0400
Message-ID: <JKqdnfD7vJYuinTXnZ2dnUVZ_uSdnZ2d_at_giganews.com>
"paul c" <toledobythesea_at_oohay.ac> wrote in message
news:LC7Gm.49742$Db2.7559_at_edtnps83...
> Mr. Scott wrote:
> ...
>> Constraints specify what can be true, not what is supposed to be true.
>> ...
>
> I thought constraints constrain, ie., limit. (I've often thought that
> isn't enough in practice, eg., I've never seen a default defined
> algebraically and beyond that I wouldn't mind a variation on constraints
> that lets me force an assertion, eg., some tuple that is always present,
> whether the user has thought to include it or not, probably CJ Date would
> disagree with that.)
A proposition either can be true or can't be true. Specifying what can be true also specifies what can't; likewise, specifying what can't be true also specifies what can. Received on Thu Oct 29 2009 - 05:18:59 CET