Re: Relation Schemata vs. Relation Variables
From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Mon, 28 Aug 2006 08:14:12 +0200
Message-ID: <ecu1jj$e6t$1_at_orkan.itea.ntnu.no>
>
> How come ? One can easily think about a transition constraint in set
> terms by extending the original universe with a new attribute value.
> Then declarative TC specification would be no different from any other
> integrity constraint specification. That's, by the way, is what
> Dataphor does with its 'old' and 'new' values.
Date: Mon, 28 Aug 2006 08:14:12 +0200
Message-ID: <ecu1jj$e6t$1_at_orkan.itea.ntnu.no>
vc wrote:
> Marshall wrote:
> [...]
>> The idea of transition constraints is inherrently non-set-theoretic, >> because it assumes tuple-identity.
>
> How come ? One can easily think about a transition constraint in set
> terms by extending the original universe with a new attribute value.
> Then declarative TC specification would be no different from any other
> integrity constraint specification. That's, by the way, is what
> Dataphor does with its 'old' and 'new' values.
I don't understand your reference to Dataphor here. Dataphor's transition constraints are tuple-based, and aren't enforced usefully when using relvar assignment (as opposed to insert/update/delete).
-- JonReceived on Mon Aug 28 2006 - 08:14:12 CEST