Re: Getting Normal Forms *wrong*. Is there actual disagreement on what 1NF > 3NF means or is this sloppiness or ignorance on authors' parts?
Date: Sat, 08 Aug 2009 00:48:24 GMT
Message-ID: <sX3fm.40001$PH1.25980_at_edtnps82>
David Portas wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4a7c6737$0$23786$9a566e8b_at_news.aliant.net...
>>> Here's something I really need clarification on. Is it the case, or is >>> it *not* the case, that 2NF "only applies" in cases where there is a >>> composite key? >> It is the case. >>
>
> Here's a relation:
>
> Triangles {Id*, Area, SumOfAngles}
>
> * = key. The following dependency holds because the sum of the angles of any
> triangle is a constant:
>
> {}->{SumOfAngles}
>
> {} (the empty set) is a proper subset of the key {Id} and {}->{SumOfAngles}
> is a dependency on only part of the key. Triangles is a relation without a
> composite key and it violates 2NF. I don't see why 2NF shouldn't apply to
> this case, even though it's unusual and not especially interesting.
>
I think this a very nice example of something that I don't know the name for! (a kind of tautology maybe?) I guess this example is not applicable to trapezoids. What if nobody in the enterprise knows geometry? The example I like is {name*, state, zipcode}.; For convenience, I might choose to ignore the fact that state determines zipcode (or does it? - I think I remember reading that a few obscure zipcodes span states, or if they don't, that they might in the future!). My attitude is that there is always somebody who knows more about a subject than I do, but they might not be available when I need them. This reminds me how upset I get when people want a db to record every possible fact, not just the ones that the present application needs. But thanks for posting it, it's a good one to remember.. Received on Sat Aug 08 2009 - 02:48:24 CEST