Re: looking for a term

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 09 Jul 2005 22:44:37 GMT
Message-ID: <prYze.1921603$6l.645151@pd7tw2no>

mAsterdam wrote:
> paul c wrote:
> ...
> How would they differ in meaning?

perhaps i shouldn't have said 'meaning'. more straightforward to just say the ternary relation has a (implied) constraint that the two binary ones don't. actually several - eg if employee has a number, then employee must have a name and an address.

>> 2) if i natural join N and A, producing a result that matches the 
>> contents of E, am i introducing the constraint in some sense?

>
>
> Only for the resulting view - but I'm not sure what you mean here.
> If it is enforced as a constraint - how could you
> insert into A - or into N?

i guess if the constraint, implied or not, applies only to the view then inserts to A or N wouldn't be affected. if it were somehow enforced for A or N (for example, if A.emp# was a foreign key E.emp# and vice-versa, even if that seems a bizarre way to do it and similarly for N.emp#), then some 'transaction' mechanism would be needed for separate insert 'statements' to succeed, but that's another topic, i think.

perhaps the implied constraint i'm talking about is nothing more than a fancy way to say that nulls aren't allowed.

p Received on Sat Jul 09 2005 - 17:44:37 CDT