Re: On Formal IS-A definition
From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 12 May 2010 05:12:29 GMT
Message-ID: <1NqGn.3928$z%6.3787_at_edtnps83>
>> Erwin wrote:
>>
>>> On 11 mei, 19:02, paul c <toledobythe..._at_oohay.ac> wrote:
>>
>> ...
>>
>>>> (I didn't have RVA's in mind, more what you might call
>>>> Set-Valued-Attributes and those certainly do need some basis for
>>>> interpretation, eg., perhaps a tuple with an empty set of parts would
>>>> need to be meaningless in the face of the closed-world-assumption.
>>>
>>> Not always.
>>>
>>> Suppliers who supply packagings of no parts at all are pretty insane.
>>>
>>> But relvar keys that consist of no attributes at all are not. Thus a
>>> catalog tuple describing a relvar key with an empty set of attributes
>>> most certainly will not "need to be meaningless in the face of the
>>> CWA". Quite the contrary, in fact.
>>> ...
>>
>> But why record it? Another case might be the combinations of parts
>> that have ever been shipped by each supplier. Is there a good reason
>> to record every supplier for whom the combination is an empty set.
Date: Wed, 12 May 2010 05:12:29 GMT
Message-ID: <1NqGn.3928$z%6.3787_at_edtnps83>
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)? Not saying there is an easy way given the conventional approaches. I think Erwin hinted at one problem earlier, how can the empty set of parts co-exist with a non-empty set (his case 'b' where no key is specified), eg., a supplier has no parts and some parts simultaneously. Received on Wed May 12 2010 - 07:12:29 CEST