Re: No exceptions?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 30 Jun 2006 18:35:48 GMT
Message-ID: <8aepg.4222$pu3.99458_at_ursa-nb00s0.nbnet.nb.ca>
>
> I think it is a bit misleading to consider ungroup an example of extend.
> For one thing: The extend operator as normally defined does not affect
> cardinality; ungroup does (in general).
Date: Fri, 30 Jun 2006 18:35:48 GMT
Message-ID: <8aepg.4222$pu3.99458_at_ursa-nb00s0.nbnet.nb.ca>
Jon Heggland wrote:
> Bob Badour wrote:
>
>>The extend operation creates a new relation by adding an attribute to an >>existing one. Strictly speaking, whether the candidate key would be >>preserved depends on the operation used to derive the extended >>attributes. Ungrouping a relation valued attribute, for instance, would >>affect the key. However, most familiar extend operations would not.
>
> I think it is a bit misleading to consider ungroup an example of extend.
> For one thing: The extend operator as normally defined does not affect
> cardinality; ungroup does (in general).
I find it misleading to consider it anything else. Received on Fri Jun 30 2006 - 20:35:48 CEST