Re: compound propositions

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 30 Mar 2010 10:42:28 -0300
Message-ID: <4bb1ffc5$0$12432$9a566e8b_at_news.aliant.net>

David BL wrote:
> On Mar 30, 10:59 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>

>>Mr. Scott wrote:
>>
>>
>>>Nulls are not nonsense.  They're merely a device that permits the recording
>>>of disjunctive information in neat tabular format.
>>
>>Explain how that requires breaking useful identies like
>>
>>SUM(A) + SUM(B) = SUM(A+B)
>>
>>create table tablewithnulls(A integer, B integer)
>>
>>insert into tablewithnulls values(1,NULL)
>>insert into tablewithnulls values(NULL,2)
>>insert into tablewithnulls values(3,4)
>>
>>select SUM(A) from tablewithnulls      -- 4
>>select SUM(B) from tablewithnulls      -- 6
>>select SUM(A+B) from tablewithnulls    -- 7 != 4+6

>
>
> I think under Zaniolo's no-information interpretation of NULL,
> tablewithnulls can be regarded as simultaneously encoding the
> following relations without NULLs:
>
> A
> ---
> 1
> 3
>
> B
> ---
> 2
> 4
>
> A' B'
> ------
> 3 4
>
> Note the following:
>
> SUM(A) = 4
> SUM(B) = 6
> SUM(A') = 3
> SUM(B') = 4
> SUM(A'+B') = 7
> SUM(A') + SUM(B') = SUM(A'+B')
In other words, one can represent the same thing with proper relations (ie. no null and no duplicates) while preserving the identity. Good to know. Received on Tue Mar 30 2010 - 15:42:28 CEST