Re: On Formal IS-A definition
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 12 May 2010 10:51:41 -0300
Message-ID: <4beab274$0$12430$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."
Date: Wed, 12 May 2010 10:51:41 -0300
Message-ID: <4beab274$0$12430$9a566e8b_at_news.aliant.net>
paul c wrote:
> Bob Badour wrote: >
>> 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."
> > I'm guessing that you mean the utility of keys with no attributes. But > what if there's another way to specify them that doesn't involve empty > sets (or RVA's if you like)?
Keys with zero attributes don't requires RVA's. Hence my suggestion to re-read with greater care. Received on Wed May 12 2010 - 15:51:41 CEST