Re: A simple notation, again
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 17 Jul 2007 14:12:05 -0300
Message-ID: <469cf840$0$8863$9a566e8b_at_news.aliant.net>
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> news:4kWmi.125098$1i1.56624_at_pd7urf3no...
>> ...
>>
>>> Also, this gives me an excuse to mention one of my pet penchants
>>> again. <NOT> (A <OR> B) is the complement of a union in D&D terms and
>>> when A <OR> B is true, it implies that (<NOT> A) <AND> (<NOT> B) is
>>> false. I find it interesting to think about a relation's complement
>>> when thinking about insert to "union". When A and B have the same
>>> heading and we insert a single tuple to a view that is A <OR> B, some
>>> people say inserting to one or the other of A or B is just as logical
>>> as inserting to both A and B, so we can't really decide what to do.
>>> But it seems reasonable to me that the complement of the view must
>>> also respect the complements of A and B, so neither of those
>>> complements should contain the inserted tuple, which means that both
>>> A and B would contain it after the insert.
>>
>> I don't think this is quite right.
>>
>> Suppose t is a tuple whose presence in A or in B would not violate any
>> constraints. Then t must necessarily be an element of either A or its
>> complement, and t must necessarily be an element of either B or its
>> compliment. Now, if t does not appear in A union B, then t must
>> necessarily be an element of both the complement of A and the
>> complement of B. As a result, an insert of t into the view, A union
>> B, does not map to any one of these operations: (1) an insert of t
>> into A, (2) an insert of t into B, or (3) an insert of t into both A
>> and B.
>> ...
Date: Tue, 17 Jul 2007 14:12:05 -0300
Message-ID: <469cf840$0$8863$9a566e8b_at_news.aliant.net>
paul c wrote:
> Brian Selzer wrote: >
>> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>> news:4kWmi.125098$1i1.56624_at_pd7urf3no...
>> ...
>>
>>> Also, this gives me an excuse to mention one of my pet penchants
>>> again. <NOT> (A <OR> B) is the complement of a union in D&D terms and
>>> when A <OR> B is true, it implies that (<NOT> A) <AND> (<NOT> B) is
>>> false. I find it interesting to think about a relation's complement
>>> when thinking about insert to "union". When A and B have the same
>>> heading and we insert a single tuple to a view that is A <OR> B, some
>>> people say inserting to one or the other of A or B is just as logical
>>> as inserting to both A and B, so we can't really decide what to do.
>>> But it seems reasonable to me that the complement of the view must
>>> also respect the complements of A and B, so neither of those
>>> complements should contain the inserted tuple, which means that both
>>> A and B would contain it after the insert.
>>
>> I don't think this is quite right.
>>
>> Suppose t is a tuple whose presence in A or in B would not violate any
>> constraints. Then t must necessarily be an element of either A or its
>> complement, and t must necessarily be an element of either B or its
>> compliment. Now, if t does not appear in A union B, then t must
>> necessarily be an element of both the complement of A and the
>> complement of B. As a result, an insert of t into the view, A union
>> B, does not map to any one of these operations: (1) an insert of t
>> into A, (2) an insert of t into B, or (3) an insert of t into both A
>> and B.
>> ...
> > I mentioned "insert ... to a view" but I think I shouldn't have, because > dbms's don't insert into views!
But they damned well should! Received on Tue Jul 17 2007 - 19:12:05 CEST