Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!newsfeed00.sul.t-online.de!newsfeed01.sul.t-online.de!t-online.de!newsfeed.cw.net!cw.net!news-FFM2.ecrc.de!news.tele.dk!news.tele.dk!small.news.tele.dk!uninett.no!ntnu.no!not-for-mail From: Jon Heggland Newsgroups: comp.databases.theory Subject: Re: Foreign superkey support Date: Tue, 08 Aug 2006 07:18:48 +0200 Organization: Norwegian university of science and technology Lines: 16 Message-ID: References: NNTP-Posting-Host: coleburn.idi.ntnu.no Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Trace: orkan.itea.ntnu.no 1155014427 728 129.241.111.99 (8 Aug 2006 05:20:27 GMT) X-Complaints-To: usenet@itea.ntnu.no NNTP-Posting-Date: Tue, 8 Aug 2006 05:20:27 +0000 (UTC) User-Agent: Thunderbird 1.5.0.5 (Windows/20060719) In-Reply-To: Xref: dp-news.maxwell.syr.edu comp.databases.theory:44062 Bob Badour wrote: > It occurs to me a superkey reference implies something less than 3rd > normal form because any attributes over and above the irreducible key > will be functionally dependent on the foreign key. In most cases (but not all) there will be normalisation issues, yes. However, the foreign superkey (FSK) will typically control the redundancy and prevent anomalies. > Why include them in the referencing relation at all? Pragmatic reasons. For instance as an alternative to an ASSERTION-type join-based constraint, which many(? most? Does anybody know?) DMBSs don't support. -- Jon