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Re: 4/17/08 - Rails & PostgreSQL, Last night's meetingwrapup

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Selena Deckelmann <selenamarie(at)gmail(dot)com>
Cc: Postgresql PDX_Users <pdxpug(at)postgresql(dot)org>, "James F(dot) Terwilliger" <jterwill(at)cecs(dot)pdx(dot)edu>
Subject: Re: 4/17/08 - Rails & PostgreSQL, Last night's meetingwrapup
Date: 2008-04-18 17:18:27
Message-ID: 1208539107.4478.245.camel@dogma.ljc.laika.com (view raw or flat)
Thread:
Lists: pdxpug
On Fri, 2008-04-18 at 09:41 -0700, Selena Deckelmann wrote:
> Many of us retired to the Lucky Lab for refreshments.

I had an interesting discussion about relational operators with James
Terwilliger.

I brought up that some people have defined a relational algebra in
terms of only two relational operators. I didn't have many of the
details at the time, but here's a link:
http://www.dcs.warwick.ac.uk/~hugh/TTM/APPXA.pdf

The only two operators they needed are relational REMOVE (projection
on all attributes other than the one removed), and relational NAND
(or relational NOR).

They also mention another operator, TCLOSE, which can be used for
operations not possible in the standard relational algebra, such as
recursion and other things that can't be guaranteed to ever finish.
TCLOSE is not necessary for defining the typical relational operators.

Regards,
	Jeff Davis




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