Re: atomic
From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Wed, 07 Nov 2007 08:39:26 +0100
Message-ID: <fgrq3h$lh9$1_at_orkan.itea.ntnu.no>
>
> I'd see it exactly as an application presumption if the catalog had a
> value in the "AMIS" table that wasn't in the "KEYS" table (unless the
> dbms didn't support empty headers as keys.)
Date: Wed, 07 Nov 2007 08:39:26 +0100
Message-ID: <fgrq3h$lh9$1_at_orkan.itea.ntnu.no>
Quoth paul c:
> Jon Heggland wrote:
>> I see no need for presumption. Without RVAs, an AMI would probably be in >> order, and by not associating any attributes with it, one would have an >> explicitly empty key, no?
>
> I'd see it exactly as an application presumption if the catalog had a
> value in the "AMIS" table that wasn't in the "KEYS" table (unless the
> dbms didn't support empty headers as keys.)
It would be in the "KEYS" relvar, but not in the "KEYATTRIBUTES" relvar, I think... though it makes little sense to discuss this without specifying the design completely.
> The single table/relvar
> allowing RVA's seems neater to me, more exact than using two relvars.
Neater, definitely. (I'm not sure what you mean by "exact".) But wasn't your argument that RVAs are messy because of (perceived) possibility of inconsistency? Anyway, the structural design is neater, but the constraint to ensure that the key attributes are in fact attributes in the key's relvar, might be more complicated.
-- JonReceived on Wed Nov 07 2007 - 08:39:26 CET