Article View: net.database
Article #278Re: Problem with relational theory
From: Allen Van Gelder
Date: Fri, 05 Sep 1986 23:25
Date: Fri, 05 Sep 1986 23:25
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1530 bytes
I disagree with Hoffman's attempted justification of the way Eric Carleen's query is handled. Having a calculus-based language loses its point if the user has to know how the system is going to translate it to relational algebra, possibly incorrectly. His query, essentially: retrieve t1 where t1.name = t2.name or t1.name = t3.name has an obvious meaning in relational calculus, and he has a right to expect the answer to be based on this meaning. The correct way to translate an "or" in a selection is as a union. This is shown in "Principles of DB Systems," by J.D. Ullman in proving that relational algebra has the same power as relational calculus. If some system chooses a different route, it is that system's responsibility to get it right. Anything else is like defining the meaning of a program to be the machine code produced by the compiler -- easy to implement, but not very useful. Maybe IBM can run this bluff, but I doubt RTI can.
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Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: arc1-ca.pugleaf.net!utzoo!watmath!clyde!caip!nike!oliveb!glacier!navajo!avg From: avg@navajo.STANFORD.EDU (Allen Van Gelder) Newsgroups: net.database Subject: Re: Problem with relational theory Message-ID: <819@navajo.STANFORD.EDU> Date: Fri, 5-Sep-86 19:25:56 EDT Article-I.D.: navajo.819 Posted: Fri Sep 5 19:25:56 1986 Date-Received: Sun, 7-Sep-86 03:24:38 EDT References: <595@ur-tut.UUCP> <452@hdsvx1.UUCP> Reply-To: avg@navajo.UUCP (Allen Van Gelder) Organization: Stanford University Lines: 18