Re: Nulls, integrity, the closed world assumption and events
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 09 Jan 2007 02:01:57 GMT
Message-ID: <pICoh.42524$cz.622548_at_ursa-nb00s0.nbnet.nb.ca>
>>Marshall wrote:
>>
>>>On Jan 8, 4:44 am, "David" <davi..._at_iinet.net.au> wrote:
>>
>>>>My point is that the following six conditions can't all be satisfied at
>>>>once
>>>> C1. use person(P,M,F) relation
>>>> C2. don't allow nulls in M,F
>>>> C3. enforce referential integrity on M,F
>>>> C4. only allow finite number of persons in the domain
>>>> C5. there are no cycles in the family tree
>>>> C6. there is at least one person
>>
>>>>Obviously we must have C4, C5 and allow C6. I suggest that C2,C3 are
>>>>important and therefore C1 should be dropped. ie the person(P,M,F)
>>>>relation itself is "bad". Do you agree?
>>
>>>This analysis looks right to me.
>>
>>Huh? Your solution basically achieves all of the above with the
>>inconsequential difference that you used a different name for the
>>relation in C1.
Date: Tue, 09 Jan 2007 02:01:57 GMT
Message-ID: <pICoh.42524$cz.622548_at_ursa-nb00s0.nbnet.nb.ca>
Marshall wrote:
> On Jan 8, 5:06 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote: >
>>Marshall wrote:
>>
>>>On Jan 8, 4:44 am, "David" <davi..._at_iinet.net.au> wrote:
>>
>>>>My point is that the following six conditions can't all be satisfied at
>>>>once
>>>> C1. use person(P,M,F) relation
>>>> C2. don't allow nulls in M,F
>>>> C3. enforce referential integrity on M,F
>>>> C4. only allow finite number of persons in the domain
>>>> C5. there are no cycles in the family tree
>>>> C6. there is at least one person
>>
>>>>Obviously we must have C4, C5 and allow C6. I suggest that C2,C3 are
>>>>important and therefore C1 should be dropped. ie the person(P,M,F)
>>>>relation itself is "bad". Do you agree?
>>
>>>This analysis looks right to me.
>>
>>Huh? Your solution basically achieves all of the above with the
>>inconsequential difference that you used a different name for the
>>relation in C1.
> > I'm a little unclear who the "you" in the "your solution basically" > sentence > above is, since I didn't propose a solution. I just agreed with the > claim that we can't simultaneously satisfy C1 - C6.
D'Oh! It was JOG's solution. My bad. Received on Tue Jan 09 2007 - 03:01:57 CET