Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!news-FFM2.ecrc.net!newsfeed00.sul.t-online.de!t-online.de!inka.de!not-for-mail
From: "Felix E. Klee" <felix.klee@inka.de>
Newsgroups: comp.databases.theory
Subject: Re: How to ensure data consistency?
Date: Thu, 9 Sep 2004 12:07:32 +0200
Organization: (Posted via) INKA e.V. http://www.inka.de/
Lines: 18
Message-ID: <20040909120732.6c7b769a.felix.klee@inka.de>
References: <3lmnj0tdqs6n98so05hslbs6b0rjqkkdk7@4ax.com>
 <fo-dnaxhxYtECabcRVn-uA@comcast.com>
 <7dhqj057v2nb3jvgig151psbhl1mg9hrsm@4ax.com>
 <PP-dnUj6cu9gX6HcRVn-oQ@comcast.com>
 <3fsrj0lpe76pfvfjfe1ur2ubpb3hqu69fg@4ax.com>
 <vBw%c.6339$BQ4.1607@trnddc06>
 <sXw%c.6825$Q44.760@trnddc09>
NNTP-Posting-Host: puric.inka.de
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-Trace: sapa.inka.de 1094724711 26319 193.197.184.17 (9 Sep 2004 10:11:51 GMT)
X-Complaints-To: abuse@inka.de
NNTP-Posting-Date: 9 Sep 2004 10:11:51 GMT
X-Newsreader: Sylpheed version 0.9.9 (GTK+ 1.2.10; i486-slackware-linux-gnu)
Xref: dp-news.maxwell.syr.edu comp.databases.theory:25881

On Wed, 08 Sep 2004 05:40:40 GMT Dan wrote:
> > If the DBMS supports deferred constraint mechanisms, I circular
> > Foreign Key constraint relationship will work.  [snip]
> 
> This won't work with multiple subtypes, either overlapping or
> disjoint; only mutual existence dependence relationships that are one
> to one.  But triggers will do just fine.  Front end enforcement is not
> always necessary.

Even in the case where the specialization types are mutually exclusive,
I don't see how circular foreign key constraints can be utilized. What
should the bipartite primary key in the main table reference if used as
a foreign key?

Thus, using Joe Celko's solution, there still is the problem that the
main table may contain entries for which there are no subtables.

Felix