Re: Foreign superkey support
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 08 Aug 2006 12:26:40 GMT
Message-ID: <4q%Bg.36766$pu3.483816_at_ursa-nb00s0.nbnet.nb.ca>
>
> In most cases (but not all) there will be normalisation issues, yes.
> However, the foreign superkey (FSK) will typically control the
> redundancy and prevent anomalies.
>
>
> Pragmatic reasons. For instance as an alternative to an ASSERTION-type
> join-based constraint, which many(? most? Does anybody know?) DMBSs
> don't support.
Date: Tue, 08 Aug 2006 12:26:40 GMT
Message-ID: <4q%Bg.36766$pu3.483816_at_ursa-nb00s0.nbnet.nb.ca>
Jon Heggland wrote:
> Bob Badour wrote:
>
>>It occurs to me a superkey reference implies something less than 3rd >>normal form because any attributes over and above the irreducible key >>will be functionally dependent on the foreign key.
>
> In most cases (but not all) there will be normalisation issues, yes.
> However, the foreign superkey (FSK) will typically control the
> redundancy and prevent anomalies.
>
>>Why include them in the referencing relation at all?
>
> Pragmatic reasons. For instance as an alternative to an ASSERTION-type
> join-based constraint, which many(? most? Does anybody know?) DMBSs
> don't support.
I don't follow your reasoning. If you simply omitted the dependent attributes from the referencing relation, normal foreign key constraints would suffice. Received on Tue Aug 08 2006 - 14:26:40 CEST