Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!drn.maxwell.syr.edu!news.maxwell.syr.edu!feeder2.on.meganewsservers.com!textfeed1.on.meganewsservers.com!meganewsservers.com!reader1.on.meganewsservers.com!reader1.on.meganewsservers.com!not-for-mail ath: nntpswitch.com Date: Mon, 29 Nov 2004 16:05:48 -0800 From: Tom Hester Organization: The Metadata Company User-Agent: Mozilla Thunderbird 0.7.1 (Windows/20040626) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.databases.theory Subject: Re: Logical equivalence of simple and complex types under the relational model? References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Message-ID: Lines: 19 NNTP-Posting-Host: 216.251.47.166 X-Trace: 1101773023 reader1.on.meganewsservers.com 16681 216.251.47.166:40605 Xref: dp-news.maxwell.syr.edu comp.databases.theory:28688 Rene de Visser wrote: > I have read a number of papers that discuss whether complex data types > should be allowed under the relational model. > > What I haven't seen analysed is whether there is actually any logical > difference (upto renaming/isomorphism) between the resulting models. languages) it makes no logical difference? > > Rene. > > > If you mean literally a logical difference, then there is. The easiest way of thinking of logic and databases is to think of the data model as an interpretation of a language. If the model is composed only of simple types then the language is first order function free--the kind of logic that we all learned as undergraduates. If the model allows complex types then the language is no longer function free--it is more complex, allowing functions that define the abstract types.