Path: news.cambrium.nl!textnews.cambrium.nl!feeder1.cambriumusenet.nl!feed.tweaknews.nl!195.208.113.1.MISMATCH!goblin3!goblin.stu.neva.ru!pit-transit.telstra.net!news.telstra.net!news-server.bigpond.net.au!53ab2750!not-for-mail Subject: Re: More on identifiers From: "Joe Thurbon" Content-Type: text/plain; format=flowed; delsp=yes; charset=utf-8 MIME-Version: 1.0 Newsgroups: comp.databases.theory References: <03132046-3fd2-4bb1-9e00-cd81ece451c2@h2g2000yqg.googlegroups.com> Content-Transfer-Encoding: 7bit Message-ID: User-Agent: Opera Mail/9.64 (MacIntel) Lines: 22 Date: Sat, 06 Jun 2009 04:19:43 GMT NNTP-Posting-Host: 121.208.0.127 X-Complaints-To: abuse@bigpond.net.au X-Trace: news-server.bigpond.net.au 1244261983 121.208.0.127 (Sat, 06 Jun 2009 14:19:43 EST) NNTP-Posting-Date: Sat, 06 Jun 2009 14:19:43 EST Organization: BigPond Internet Services Xref: news.cambrium.nl On Fri, 05 Jun 2009 14:52:27 +1000, David BL wrote: [...] > > Due to the projection, all the abstract identifiers have disappeared > from every relation. In a way, it's like seeing a database within a > database! The value of the "inner" database records all the facts in > the /context/ of just one of the items, and therefore has no need for > abstract identifiers to glue things together. > I may have misunderstood, but haven't you just moved the 'problem'? That is, each abstract identifier that you want to get rid of ends up with 'its own database'. Two database values that came from entities that differed only by their abstract identifier will not be distinguishable. So to distinguish between them, the abstract identifiers and up being arbitary names of databases. By the way, I really liked your motivating example and analysis. Cheers, Joe