Re: more on delete from join

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 26 Aug 2009 21:24:12 -0300
Message-ID: <4a95d232$0$23753$9a566e8b_at_news.aliant.net>


paul c wrote:

> Tegiri Nenashi wrote:
>

>> On Aug 26, 2:14 pm, paul c <toledobythe..._at_oohay.ac> wrote:
>>
>>> Tegiri Nenashi wrote:
>>>
>>>> On Aug 26, 1:03 pm, paul c <toledobythe..._at_oohay.ac> wrote:
>>>>
>>>>> I meant "AND" as the logical connective, not shorthand for relational
>>>>> "<AND>".  "R AND A" stands for a logical conjunction of propositions,
>>>>> each proposition having been concluded to be true.  
>>>>
>>>> Stop right there. You were writing R UNION A, so R and A are relations
>>>> (or predicates) and not propositions. ...
>>>
>>> Okay, I'll stop right there and be even more precise, relations are not
>>> predicates, they are representations of predicates.  
>>
>> Can you express the difference formally? I would insist relations and
>> predicates being the same thing. ...

>
> I don't see how, except very casually. A relation is a set of ruples
> which is not the same thing as an intension or an extension but a
> relation can represent those to some extent if certain devices like
> equality and conventions like the CWA are used and the practicalities of
> recording negations can be avoided. A relational algebra expression
> can also stand in for a set of tuples, so it too could represent an
> intension or extension, but representing something is not the same as
> being the something.
>
> Maybe the apparent difficulty in seeing the conclusion would go away if
> the analogy of two different roads to the same destination is used. Not
> very complicated if you ask me, nothing to do with infinite predicates
> either.

Wouldn't it be easier to just say tuples are propositions? Received on Thu Aug 27 2009 - 02:24:12 CEST

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