Path: newssvr20.news.prodigy.com!newsmst01.news.prodigy.com!prodigy.com!prodigy.com!in.100proofnews.com!in.100proofnews.com!landlord!stones.force9.net.POSTED!not-for-mail From: Paul User-Agent: Mozilla Thunderbird 0.5 (X11/20040306) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.databases.theory Subject: Re: when to use multiple databases References: In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Lines: 29 Message-ID: Date: Sun, 04 Apr 2004 15:15:14 +0100 NNTP-Posting-Host: 212.56.100.9 X-Complaints-To: abuse@plus.net.uk X-Trace: stones.force9.net 1081087990 212.56.100.9 (Sun, 04 Apr 2004 15:13:10 BST) NNTP-Posting-Date: Sun, 04 Apr 2004 15:13:10 BST Organization: Customer of PlusNet Xref: newssvr20.news.prodigy.com comp.databases.theory:24983 Well I guess in theory the entire world only needs a single database. Of course in practice this isn't done, but I think I'm right in saying this is for physical reasons. Namely the problems of finding a DBMS to run it on. Also the problems of the single namespace for tables. You'd end up encoding a kind of hierarchical naming convention in the table names: CountyA_CompanyB_DeptC_Sales or whatever. Not to mention the political problem of who controls access etc. It does raise the question: does the "database" structure serve any theoretical purpose? Or could we just have a "Universe" that contains tables, etc.? Going the other way, might it be useful to have databases grouped together? But then you're going down the road of hierarchies which aren't nice for first-order logic. > The DBMS I'm using (Postgresql) doesn't allow cross-database queries, Speaking more practically now, I think this is your deciding factor: use a single database. > When is it wise/practical to use multiple databases if all those > databases have the same schema? Speaking theoretically I'd say never. But there may be physical reasons for it. Paul.