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Re: Modelling Disjoint Subtypes

From: Dimitri Furman <dfurman_at_cloud99.net>
Date: Wed, 28 Mar 2007 20:08:14 -0000
Message-ID: <Xns9901A3F28BAABdfurmancloud99@127.0.0.1>


On Mar 28 2007, 10:39 am, "V.J. Kumar" <vjkmail_at_gmail.com> wrote in news:Xns99016C61C8E14vdghher_at_194.177.96.26:

> "David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in
> news:1175074877.506103.251950_at_e65g2000hsc.googlegroups.com:
>

>> Yet another answer is addressed by Date in McGovern with their
>> "Orthogonal Design" principle. Potential ambiguity is created if the
>> same predicate is represented in multiple places in the schema
>> because of multiple relvars with meanings that "overlap".
>> http://www.dbdebunk.com/page/page/622331.htm

>
> But we are discussing the disjoint case such that thanks to the
> constraints the meanings do not overlap.

But see Section 8 in Part 2 of the above article. It is not that just the meanings of two base relvars should not overlap - the meanings of two distinct projections of these relvars should not overlap either.

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Received on Wed Mar 28 2007 - 15:08:14 CDT

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