Re: Guessing?

From: Brian Selzer <brian_at_selzer-software.com>
Date: Tue, 8 Jul 2008 13:22:26 -0400
Message-ID: <InNck.11653$cW3.9262@nlpi064.nbdc.sbc.com>

"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:48738203$0$4049$9a566e8b_at_news.aliant.net...
> paul c wrote:
>
>> Brian Selzer wrote:
>>
>>> "paul c" <toledobysea_at_ac.ooyah> wrote in message
>>
>> ...
>>
>>>> However, I'm content to say that all three relations have the same
>>>> predicate, assuming no attribute renaming is involved in your
>>>> interpretation. I know many people say that the 'or' is introduced to
>>>> the predicate of R. I don't believe there is any law or principle,
>>>> including relational closure, that requires anybody to think this way.
>>>>
>>>
>>> How can they have the same predicate if they can have different
>>> extensions? That doesn't make any sense.
>>> ...
>>
>> They are misconceived. The example strikes me as akin to Joe C's word
>> games.
>
> To answer Selzer's query, they have different external predicates but the
> same predicate as far as the DBMS can calculate.

That doesn't make sense either. If there are different external predicates, then shouldn't that be reflected by there being different relation names, and thus differing internal predicates? Received on Tue Jul 08 2008 - 12:22:26 CDT

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