Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!postnews.google.com!i3g2000cwc.googlegroups.com!not-for-mail From: "Keith H Duggar" Newsgroups: comp.databases.theory Subject: Re: Multiple keys and transition constraints Date: 15 Sep 2006 18:34:19 -0700 Organization: http://groups.google.com Lines: 52 Message-ID: <1158370459.256735.186160@i3g2000cwc.googlegroups.com> References: NNTP-Posting-Host: 71.249.12.72 Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" X-Trace: posting.google.com 1158370464 19797 127.0.0.1 (16 Sep 2006 01:34:24 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Sat, 16 Sep 2006 01:34:24 +0000 (UTC) In-Reply-To: User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/312.8 (KHTML, like Gecko) Safari/312.6,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: i3g2000cwc.googlegroups.com; posting-host=71.249.12.72; posting-account=Rev6_g0AAAB1AAaRVYv5bhpO6TyThktx Xref: dp-news.maxwell.syr.edu comp.databases.theory:44903 Brian Selzer wrote: > Given a relation schema R {A, B, C}, where A and B are > each candidate keys. > > If the current extension is > > r {{A:1, B:9, C:3} > {A:2, B:8, C:4}} > > and the proposed extension is > > r' {{A:1, B:8, C:4} > {A:2, B:9, C:3}} > > is only A different? Or are both B and C different? From > one perspective, both B and C remain constant but A is > different. From another perspective, A remains constant > but both B and C are different. What is A? What is B? What is C? When you say "is only A different", what if I respond "no, A is A"? Is A a symbol denoting a set? If so then A denotes {1,2} in extension r and A denotes {1,2} in extension r'. Thus that which A denotes remains unchanged in r and r'; and in that sense "A is not different". And neither are B nor C different. Or does A denote a domain {0,1,2,...} for example? If so then perhaps A, B, and C never become "different". Or look at it this way. A, B, and C do not become different any more than 1, 2, 3, 4, 8, and 9 become different. Has 1 changed? Or is only 4 different? What is different are the two extensions r and r'; what is different are the tuples that compose r and r'; what is not different are the ever constant /values/ that compose those tuples. This is the semantic gulf in which many of your arguments have drowned. When you say "is only A different?", it seems that you have in mind some implicit thing, other than A, that you hold /is/ A. Some physical storage perhaps? It is the view you have, that A /is/ a thing other than a symbol denoting either a domain, extension, or property that separates you from many against whom you have butted heads recently. Because your notion seems rather physical. Ie that by A you mean some storage space or memory location. If it is not physical, then it's up to you to provide a clear (and concise) explanation of what you mean by A. -- Keith -- Fraud 6