Path: text.usenetserver.com!out01a.usenetserver.com!news.usenetserver.com!in02.usenetserver.com!news.usenetserver.com!postnews.google.com!news2.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!nx01.iad01.newshosting.com!newshosting.com!post01.iad01!news.aliant.net!not-for-mail Date: Mon, 03 Mar 2008 18:24:03 -0400 From: Bob Badour User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.databases.theory,comp.object Subject: Re: Object-relational impedence References: <0cd61579-0f26-422c-9aec-908ffdea59ff@i7g2000prf.googlegroups.com> <47cc494c$0$4037$9a566e8b@news.aliant.net> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Lines: 45 Message-ID: <47cc7a87$0$4031$9a566e8b@news.aliant.net> NNTP-Posting-Host: 142.176.57.92 X-Complaints-To: abuse@aliant.net Xref: usenetserver.com comp.databases.theory:170264 comp.object:264434 X-Received-Date: Mon, 03 Mar 2008 17:24:11 EST (text.usenetserver.com) topmind wrote: > On Mar 3, 10:54 am, Bob Badour wrote: > >>topmind wrote: >> >>>JOG wrote: >> >>>>On Mar 3, 2:07 pm, Thomas Gagne wrote: >> >>>>>All attempts by applications to access a DB's tables and columns >>>>>directly violates design principles that guard against close-coupling. >>>>>This is a basic design tenet for OO. Violating it when jumping from OO >>>>>to RDB is, I think, the source of problem that are collectively and >>>>>popularly referred to as the object-relational impedance mismatch. >> >>>>I wondered if we might be able to come up with some agreement on what >>>>object-relational impedence mismatch actually means. I always thought >>>>the mismatch was centred on the issue that a single object != single >>>>tuple, but it appears there may be more to it than that. >> >>>>I was hoping perhaps people might be able to offer perspectives on the >>>>issues that they have encountered. One thing I would like to avoid >>>>(outside of almost flames of course), is the notion that database >>>>technology is merely a persistence layer (do people still actually >>>>think that?) - I wonder if the 'mismatch' stems from such a >>>>perspective. >> >>>This came up in a nearby message. I borrowed the following text from >>>wikipedia: >> >>The text had too many blatant errors to start enumerating them all. > > Most of them are statements about philosophy or practice rather than > absolutes; thus its hard for them to be objectively or "blatantly" > wrong. Whether that's a good thing or not is another issue. I see the > list as a starting point for discussion even if it does not settle > everything. > > It brings up interesting questions, such as why not have schema > inheritance? If inheritance is good or OO, why is it not good for > relational schema's? The answer is that OO and relational approach > things differently. Your question presupposes that inheritance is good for OO.