Path: news.cambrium.nl!textnews.cambrium.nl!feeder1.cambriumusenet.nl!feed.tweaknews.nl!193.201.147.73.MISMATCH!border2.nntp.ams.giganews.com!nntp.giganews.com!news-out1.kabelfoon.nl!newsfeed.kabelfoon.nl!xindi.nntp.kabelfoon.nl!newsfeed2.telusplanet.net!newsfeed.telus.net!edtnps82.POSTED!7564ea0f!not-for-mail From: paul c User-Agent: Thunderbird 2.0.0.22 (Windows/20090605) MIME-Version: 1.0 Newsgroups: comp.databases.theory Subject: Re: Getting Normal Forms *wrong*. Is there actual disagreement on what 1NF > 3NF means or is this sloppiness or ignorance on authors' parts? References: <87e06e65-31bd-4c40-b85f-d163cb13894e@k26g2000vbp.googlegroups.com> <4a7c6737$0$23786$9a566e8b@news.aliant.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Lines: 36 Message-ID: Date: Sat, 08 Aug 2009 00:48:24 GMT NNTP-Posting-Host: 75.155.111.127 X-Trace: edtnps82 1249692504 75.155.111.127 (Fri, 07 Aug 2009 18:48:24 MDT) NNTP-Posting-Date: Fri, 07 Aug 2009 18:48:24 MDT Xref: news.cambrium.nl David Portas wrote: > "Bob Badour" wrote in message > news:4a7c6737$0$23786$9a566e8b@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..