Re: Newbie question about db normalization theory: redundant keys OK?
From: Brian Selzer <brian_at_selzer-software.com>
Date: Thu, 27 Dec 2007 19:58:56 -0500
Message-ID: <lTXcj.3065$lo5.1456@newssvr19.news.prodigy.net>
> I think I would have no difficulty at all. If you can show a single
> example where any such information is preserved after an update then I can
> show you the equivalent assignment to preserve the same information. It
> ought to be self-evident that such an assignment always exists.
>
Date: Thu, 27 Dec 2007 19:58:56 -0500
Message-ID: <lTXcj.3065$lo5.1456@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. I noticed that you ignored the balance of my last post.
> --
> David Portas
>
>
Received on Thu Dec 27 2007 - 18:58:56 CST