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Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]

Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]

From: Marshall Spight <marshall.spight_at_gmail.com>
Date: 10 Jun 2005 14:38:53 -0700
Message-ID: <1118439533.845148.66910@o13g2000cwo.googlegroups.com>


> Sometimes you *can* say something, even though some of the variables are
> unknown. Suppose I told you x is a natural number, could you then tell
> me whether the following statements are true:
>
> (x > 5) or (x <= 5)
> (x - x) = 0
>
> I bet you could. :-)

Hmmm. I will agree that for any unknown value of x, you can say things about that are also true for all x.

Hmmm. That makes it seem like UNKNOWN is really a universally quantified logic variable.

That sort of makes it seem like arguing for UNKNOWN values is like arguing for universally quantified logic variables, which in the
absence of unification are neither interesting nor useful. Or am I wrong?

Marshall Received on Fri Jun 10 2005 - 16:38:53 CDT

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