Re: Codd's Information Principle
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 01 Nov 2009 21:08:30 -0400
Message-ID: <4aee3110$0$5324$9a566e8b_at_news.aliant.net>
>> paul c wrote:
>>
>>> Bob Badour wrote:
>>>
>>>> paul c wrote:
>>>
>>> ...
>>>
>>>>> Didn't mean to suggest otherwise. Sometimes the immediate expert
>>>>> objection to the 'primrose path' turns out to be an advantage if
>>>>> the idea is allowed to breath.
>>>>>
>>>>> But one point seems very immediate to me - for any given relational
>>>>> expression, there is only one equivalent extension.
>>>>
>>>> I don't follow that at all.
>>>
>>> If you mean the last sentence, I could expand it by saying that for
>>> any given purpose, in other words any given application, I think that
>>> single extension must have one interpretation. Since the expression
>>> might not involve any algebraic operations, I think it is best to
>>> discard those in the interpretation, no matter how the extension was
>>> formed. I say 'best' because that seems sufficient to me and I don't
>>> see how including those ops is necessary. I would like to know what
>>> problems this causes, eg., I don't see that
>>> inconsistences/contradictions or loss of utility or inability to
>>> optimize result from it.
>>
>> I cannot make sense of what you wrote.
Date: Sun, 01 Nov 2009 21:08:30 -0400
Message-ID: <4aee3110$0$5324$9a566e8b_at_news.aliant.net>
paul c wrote:
> Bob Badour wrote: >
>> paul c wrote:
>>
>>> Bob Badour wrote:
>>>
>>>> paul c wrote:
>>>
>>> ...
>>>
>>>>> Didn't mean to suggest otherwise. Sometimes the immediate expert
>>>>> objection to the 'primrose path' turns out to be an advantage if
>>>>> the idea is allowed to breath.
>>>>>
>>>>> But one point seems very immediate to me - for any given relational
>>>>> expression, there is only one equivalent extension.
>>>>
>>>> I don't follow that at all.
>>>
>>> If you mean the last sentence, I could expand it by saying that for
>>> any given purpose, in other words any given application, I think that
>>> single extension must have one interpretation. Since the expression
>>> might not involve any algebraic operations, I think it is best to
>>> discard those in the interpretation, no matter how the extension was
>>> formed. I say 'best' because that seems sufficient to me and I don't
>>> see how including those ops is necessary. I would like to know what
>>> problems this causes, eg., I don't see that
>>> inconsistences/contradictions or loss of utility or inability to
>>> optimize result from it.
>>
>> I cannot make sense of what you wrote.
> > Best I can do at the moment without a clue or two. If Bob B doesn't get > any part of it either there is little point embellishing or possibly I > have lapsed into mysticism, will reserve judgment for now. Oh well, > that's life.
I suspect you simply do not include enough context to decipher what you are saying. If I have a relation variable, R, at any given time, its extension is simply its value. Is it not? Since R can have different values at different times, it can have more than one extension; albeit, only one at a time. Received on Mon Nov 02 2009 - 02:08:30 CET