From jcowan@reutershealth.com Thu Oct 17 12:30:15 2002 Return-Path: X-Sender: jcowan@reutershealth.com X-Apparently-To: lojban@yahoogroups.com Received: (EGP: mail-8_2_2_1); 17 Oct 2002 19:30:15 -0000 Received: (qmail 12064 invoked from network); 17 Oct 2002 19:30:14 -0000 Received: from unknown (66.218.66.218) by m8.grp.scd.yahoo.com with QMQP; 17 Oct 2002 19:30:14 -0000 Received: from unknown (HELO mail2.reutershealth.com) (65.246.141.151) by mta3.grp.scd.yahoo.com with SMTP; 17 Oct 2002 19:30:14 -0000 Received: from skunk.reutershealth.com (IDENT:cowan@[10.65.117.21]) by mail2.reutershealth.com (Pro-8.9.3/Pro-8.9.3) with SMTP id PAA25990; Thu, 17 Oct 2002 15:41:58 -0400 (EDT) Message-Id: <200210171941.PAA25990@mail2.reutershealth.com> Received: by skunk.reutershealth.com (sSMTP sendmail emulation); Thu, 17 Oct 2002 15:29:06 -0400 Subject: Re: [lojban] Re: zil To: jjllambias@hotmail.com (Jorge Llambias) Date: Thu, 17 Oct 2002 15:29:06 -0400 (EDT) Cc: lojban@yahoogroups.com In-Reply-To: from "Jorge Llambias" at Oct 17, 2002 03:57:45 PM X-Mailer: ELM [version 2.5 PL6] MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit From: John Cowan X-Yahoo-Group-Post: member; u=8122456 X-Yahoo-Profile: john_w_cowan Jorge Llambias scripsit: > This serves as a superficial analogy, but it's not quite the same thing. > zi'o expands the meaning of a selbri, a projection doesn't. A projection > just fixes the value of one of the arguments, or restricts in some way > the relationship between the arguments. zi'o goes the other way. By my understanding, what you are calling a projection is really a selection followed by a projection. Projection as such just shrinks the number of domains in the relation. The reason why new tuples can then appear in the Lojban context is because Lojban is an open world, where new relationships can appear from thin air, whereas implementations of relational algebra are closed worlds, where the tuples that initially exist are all the ones that will ever exist unless they are explicitly added. -- John Cowan http://www.reutershealth.com http://www.ccil.org/~cowan Yakka foob mog. Grug pubbawup zink wattoom gazork. Chumble spuzz. -- Calvin, giving Newton's First Law "in his own words"