Re: On Formal IS-A definition
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 12 May 2010 01:04:54 -0300
Message-ID: <4bea28ec$0$12448$9a566e8b_at_news.aliant.net>
>
> ...
>
>
> 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.
Date: Wed, 12 May 2010 01:04:54 -0300
Message-ID: <4bea28ec$0$12448$9a566e8b_at_news.aliant.net>
paul c wrote:
> 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.
/paul's/Erwin's/
Oops, make that "re-read Erwin's post with greater care." Received on Wed May 12 2010 - 06:04:54 CEST