Re: Codd's Information Principle

From: Tegiri Nenashi <tegirinenashi_at_gmail.com>
Date: Fri, 6 Nov 2009 20:07:00 -0800 (PST)
Message-ID: <508a659f-5083-413e-8715-c099dee0217a_at_f18g2000prf.googlegroups.com>


On Nov 6, 7:57 pm, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
> ...It was meant to be iterative disjunction
> of unary predicates
>
> R(x,1) v R(x,2) v R(x,3) v ...
>
> each obtained from binary predicate R(x,y) by formal substitution of
> free variable y with constant. (From RA perspective this substitution
> is projection indeed...

Oops: it's restriction (join with "y=1") followed by projection to x, or, more laconic set intersection join:

R(x,1) = R(x,y) <set intersection> "y=1" Received on Sat Nov 07 2009 - 05:07:00 CET

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