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Re: thinking about UPDATE

From: Marshall Spight <mspight_at_dnai.com>
Date: Fri, 23 Jul 2004 15:57:34 GMT
Message-ID: <OzaMc.12304$eM2.4222_at_attbi_s51> 






"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:pan.2004.07.23.08.58.40.657256_at_REMOVETHIS.pandora.be...

>




> Note that in practice you would probably not include such columns because


> they are obviously redundant.




I'm not sure I agree with that. Part of the value of time-varying relations
is the "time-varying" part. That is to say, {} as a key gives us the ability
to have a singleton in the relational world, and that is a very powerful
pattern. The variable is still useful as a variable, even though the
cardinality is limited to 0 or 1.



(Are there other tricks we can play to constrain the cardinality of a
relation? Can we constrain the cardinality to exactly 1? 1 or more?)




> Actually, theory says the same because the


> relation would not be in 3NF (or even 2NF).




Ouch! That doesn't seem right. (But of course, intuition is not a great
guide here.) Time for some more research.




Marshall
Received on Fri Jul 23 2004 - 17:57:34 CEST












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