Re: Newbie question about db normalization theory: redundant keys OK?
Date: Fri, 28 Dec 2007 01:37:34 -0000
Message-ID: <-_mdnenScLrDzunanZ2dnUVZ8sKlnZ2d_at_giganews.com>
"Brian Selzer" <brian_at_selzer-software.com> wrote in message
news:lTXcj.3065$lo5.1456_at_newssvr19.news.prodigy.net...
>
> "David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message
> news:-pudnR9srdDFSe7anZ2dnUVZ8q2dnZ2d_at_giganews.com...
>> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
>> news:j9Ocj.1147$El5.530_at_newssvr22.news.prodigy.net...
>>>
>>>>> Here is the problem with treating assignment as the only primitive
>>>>> operation. With assignment, all you have available is the before and
>>>>> after images of the data, but there may be many different
>>>>> transformations that could have produced the after image from the
>>>>> before image, and there's no way to tell which transformation actually
>>>>> occurred.
>>>>
>>>>
>>>> Yes there is.
>>>
>>> I suspect you would have a difficult time proving that.
>>>
>>
>> I think I would have no difficulty at all. If you can show a single
>> example where any such information is preserved after an update then I
>> can show you the equivalent assignment to preserve the same information.
>> It ought to be self-evident that such an assignment always exists.
>>
>
> You're sidestepping the issue. The information need not be preserved in
> the database in order to be useful: it may only be needed to decide
> whether or not to permit an update.
> In any case, your demonstration would not prove that there is /always/ a
> way to tell which transformation actually occurred.
-- David PortasReceived on Fri Dec 28 2007 - 02:37:34 CET