Path: news.easynews.com!newsfeed1.easynews.com!easynews.com!easynews!newsfeed.news2me.com!newsfeed.freenet.de!fu-berlin.de!uni-berlin.de!fw-orange-zh.active.CH!not-for-mail From: =?ISO-8859-1?Q?Leandro_Guimar=E3es_Faria_Corsetti_Dutra?= Newsgroups: comp.databases.theory Subject: Re: Requirements for update languages? Date: Mon, 11 Nov 2002 16:51:58 +0100 Lines: 33 Message-ID: References: <3dcd09f6.4600124@news.wanadoo.es> NNTP-Posting-Host: fw-orange-zh.active.ch (212.215.1.67) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Trace: fu-berlin.de 1037029918 12544738 212.215.1.67 (16 [148886]) User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.2b) Gecko/20021016 X-Accept-Language: pt-br, pt, gl, es, en-us, en, f In-Reply-To: Xref: newsfeed1.easynews.com comp.databases.theory:23547 X-Received-Date: Mon, 11 Nov 2002 08:51:45 MST (news.easynews.com) Jens Lechtenbörger wrote: > alfredo@nospam_ncs.es (Alfredo Novoa) writes: > >> On 08 Nov 2002 15:26:14 +0100, "Jens >> =?iso-8859-15?q?Lechtenb=F6rger?=" wrote: >> >> With bags the view update problem is very diferent, and a lot more >> complex. > > Are you sure? Do you have a reference? We are sure. Sorry for not having a reference handy now, but think: the way to have a view (derived relation) updateable is to be able to derive the constraints that apply to the derived relation. This is a given in the relational model. Now think about bags. How could you derive the constraints in a "derived bag", and thus insert the data? Do you see a way? No? Neither does anyone else. To be more precise, a "bag model" has never being formally defined AFAIK. -- _ / \ Leandro Guimarães Faria Corsetti Dutra +41 (21) 216 15 93 \ / http://homepage.mac.com./leandrod/ fax +41 (21) 216 19 04 X http://tutoriald.sourceforge.net./ Orange Communications CH / \ Campanha fita ASCII, contra correio HTML +41 (21) 644 23 01