Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!newscon02.news.prodigy.com!newscon06.news.prodigy.com!prodigy.net!newsfeed-00.mathworks.com!lon-transit.news.telstra.net!lon-in.news.telstra.net!news.telstra.net!news-server.bigpond.net.au!53ab2750!not-for-mail From: FrankHamersley User-Agent: Mozilla Thunderbird 1.0.2 (Windows/20050317) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.databases.theory Subject: Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens] References: <1117636456.185385.128930@g44g2000cwa.googlegroups.com> <3R6oe.1962$F7.1337@news-server.bigpond.net.au> <42a41deb$0$8723$ed2619ec@ptn-nntp-reader02.plus.net> In-Reply-To: <42a41deb$0$8723$ed2619ec@ptn-nntp-reader02.plus.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Lines: 30 Message-ID: Date: Mon, 06 Jun 2005 12:55:36 GMT NNTP-Posting-Host: 147.10.194.85 X-Complaints-To: abuse@bigpond.net.au X-Trace: news-server.bigpond.net.au 1118062536 147.10.194.85 (Mon, 06 Jun 2005 22:55:36 EST) NNTP-Posting-Date: Mon, 06 Jun 2005 22:55:36 EST Organization: BigPond Internet Services Xref: dp-news.maxwell.syr.edu comp.databases.theory:31237 Paul wrote: > mountain man wrote: >>According to this reference we can replace a null in the salary >>field with "Salary not known" and/or "Unsalaried". This has >>taken some work to do, by a database professional, to derive >>an "improved" version of the personnel table (when needed). >> >>So what? The original design schema is simply missing information >>for these elements, and this information needs to be entered, >>and/or determined and entered. > > If you replaced both "Salary unknown" and "Unsalaried" with NULLs, how > do you distinguish between the two? Without redressing the fundamental weaknesses in the schema you can't. However I remain to be convinced that the domain "overloading" used to underpin Date's example is a useful contribution to the state of the art. Frankly my first impression was to see it as justifying a steaming hot pile! There are no signs of any elegance regardless of how unsatisfactory that is to purists, although I expect Date would cite the limitations of the current technologies as largely responsible for the latent ugliness of the "null-less solution". Personally I see the better solution within the context of this thread is to have a discrete attribute with a domain of "Salaried, Unsalaried". The argument about to null or not to null (sic) is for another time. Felicitations to all, Frank.