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@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 - 10:57:34 CDT