# Re: How can I proove associtivity of natural in relational algebra?

Date: 22 Nov 2005 03:40:55 -0800

Message-ID: <1132659655.553806.227340_at_g49g2000cwa.googlegroups.com>

Mikito Harakiri wrote:

*> Filter911 wrote:
**> > Mikito Harakiri wrote:
**> > > Filter911 wrote:
*

> > > > Can someone give me a link for a full proof or something?

*> > >
**> > > Given relations A,B, and C, expand each realtion into a (possibly
**> > > infinite) relations A', B', and C' with the same set of attributes
**> > > (which is the union of the attribute sets for A, B, and C). Then, the
**> > > join of A, B and C is the intersection of A', B', and C'. Intersection
**> > > is associative.
**> >
**> > What do you mean by "expand each relation"?
**>
**> "Extend", is the opposite of "project". E.g. the relation with a single
**> attribute
**>
**> A = {(a=1), (a=2)} is exended to the attribute set {a,b} with the
**> domain of attribute b being {7,8,9} as
*

Extanding using what? Using B or C? or some new relation? any full
example or link?

If I use the union of the three then A=B=C and that's a prviate case

> A' = {(a=1, b=7),(a=1, b=8),(a=1, b=9),(a=2, b=7),(a=2, b=8),(a=2,

*> b=9))}
*

Received on Tue Nov 22 2005 - 12:40:55 CET