Re: Guessing?

From: paul c <toledobysea_at_ac.ooyah>
Date: Tue, 08 Jul 2008 17:35:24 GMT
Message-ID: <wzNck.65036$Jx.3854_at_pd7urf1no>

Brian Selzer wrote:
> "Bob Badour" <> wrote in message
> news:48738203$0$4049$

>> 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?

Since when does a predicate (ie., a conventional FOL predicate) mention a relation name?

(Surely relation names aren't anything but an implementation device.) Received on Tue Jul 08 2008 - 19:35:24 CEST

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