Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.media.kyoto-u.ac.jp!newshub.sdsu.edu!elnk-nf2-pas!elnk-pas-nf1!newsfeed.earthlink.net!pd7cy1no!pd7cy2no!shaw.ca!pd7tw2no.POSTED!53ab2750!not-for-mail
X-Trace-PostClient-IP: 24.84.208.66
From: paul c <toledobythesea@oohay.ac>
User-Agent: Thunderbird 1.5.0.4 (Windows/20060516)
MIME-Version: 1.0
Newsgroups: comp.databases.theory
Subject: Re: Foreign superkey support
References: <eb7ao5$vn3$1@orkan.itea.ntnu.no>   <u2SBg.36542$pu3.480823@ursa-nb00s0.nbnet.nb.ca>   <eb96ur$mo$1@orkan.itea.ntnu.no>   <4q%Bg.36766$pu3.483816@ursa-nb00s0.nbnet.nb.ca>   <ebaa2d$jrq$1@orkan.itea.ntnu.no>   <E_3Cg.348530$iF6.170940@pd7tw2no> <1155059837.979156.61820@n13g2000cwa.googlegroups.com>
In-Reply-To: <1155059837.979156.61820@n13g2000cwa.googlegroups.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Lines: 15
Message-ID: <HJ4Cg.349208$iF6.31975@pd7tw2no>
Date: Tue, 08 Aug 2006 18:28:55 GMT
NNTP-Posting-Host: 64.59.144.74
X-Complaints-To: abuse@shaw.ca
X-Trace: pd7tw2no 1155061735 64.59.144.74 (Tue, 08 Aug 2006 12:28:55 MDT)
NNTP-Posting-Date: Tue, 08 Aug 2006 12:28:55 MDT
Organization: Shaw Residential Internet
Xref: dp-news.maxwell.syr.edu comp.databases.theory:44073

Marshall wrote:
> paul c wrote:
>> Perhaps all I'm saying is that the basic relational algebra doesn't need
>> a foreign key concept which I admit is a deviation from the specific
>> question.
> 
> I don't think of constraints as being part of the algebra per se.
>  ...

If they aren't, I think that would mean the algebra is incomplete (and 
every relation's value could only get 'larger', until it reached the 
product of its domains' values which could then never be 'constrained' 
to a smaller set).

p