Re: On Formal IS-A definition
From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 12 May 2010 03:44:27 GMT
Message-ID: <vupGn.3925$z%6.2325_at_edtnps83>
>
> Not always.
>
> Suppliers who supply packagings of no parts at all are pretty insane.
>
> But relvar keys that consist of no attributes at all are not. Thus a
> catalog tuple describing a relvar key with an empty set of attributes
> most certainly will not "need to be meaningless in the face of the
> CWA". Quite the contrary, in fact.
> ...
Date: Wed, 12 May 2010 03:44:27 GMT
Message-ID: <vupGn.3925$z%6.2325_at_edtnps83>
Erwin wrote:
> On 11 mei, 19:02, paul c <toledobythe..._at_oohay.ac> wrote:
...
>> (I didn't have RVA's in mind, more what you might call >> Set-Valued-Attributes and those certainly do need some basis for >> interpretation, eg., perhaps a tuple with an empty set of parts would >> need to be meaningless in the face of the closed-world-assumption.
>
> Not always.
>
> Suppliers who supply packagings of no parts at all are pretty insane.
>
> But relvar keys that consist of no attributes at all are not. Thus a
> catalog tuple describing a relvar key with an empty set of attributes
> most certainly will not "need to be meaningless in the face of the
> CWA". Quite the contrary, in fact.
> ...
But why record it? Another case might be the combinations of parts that have ever been shipped by each supplier. Is there a good reason to record every supplier for whom the combination is an empty set. Received on Wed May 12 2010 - 05:44:27 CEST