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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@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 - 13:35:48 CDT

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