Re: Guessing?

From: Bob Badour <>
Date: Tue, 08 Jul 2008 15:08:48 -0300
Message-ID: <4873ad31$0$4052$>

paul c wrote:

> 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?

Usually when discussing the composition operator. f(g(x)) sort of thing.

> (Surely relation names aren't anything but an implementation device.)

I don't think I entirely agree. Received on Tue Jul 08 2008 - 20:08:48 CEST

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