Path: dp-news.maxwell.syr.edu!spool.maxwell.syr.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!news-lond.gip.net!news.gsl.net!gip.net!news.tele.dk!news.tele.dk!small.news.tele.dk!uio.no!ntnu.no!not-for-mail From: Jon Heggland Newsgroups: comp.databases.theory Subject: Re: MV Keys Date: Fri, 3 Mar 2006 09:15:09 +0100 Organization: IDI/NTNU Lines: 27 Message-ID: References: <1140928045.223226.301140@i40g2000cwc.googlegroups.com> <440185c0$0$11076$e4fe514c@news.xs4all.nl> <1140963712.820976.72300@u72g2000cwu.googlegroups.com> <4401cd8b$0$11062$e4fe514c@news.xs4all.nl> <1140981916.897576.34490@u72g2000cwu.googlegroups.com> <1141000908.277461.101140@t39g2000cwt.googlegroups.com> <1141180942.125742.288830@j33g2000cwa.googlegroups.com> <1141239957.788010.239620@j33g2000cwa.googlegroups.com> <4fDNf.1833$%a2.1316@trndny05> <1141311212.487197.167020@t39g2000cwt.googlegroups.com> <1141320627.995968.219210@i40g2000cwc.googlegroups.com> <1141372781.078243.197630@e56g2000cwe.googlegroups.com> NNTP-Posting-Host: coleburn.idi.ntnu.no Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit X-Trace: orkan.itea.ntnu.no 1141377313 12937 129.241.111.99 (3 Mar 2006 09:15:13 GMT) X-Complaints-To: usenet@itea.ntnu.no NNTP-Posting-Date: Fri, 3 Mar 2006 09:15:13 +0000 (UTC) User-Agent: MicroPlanet-Gravity/2.60.2060 Xref: dp-news.maxwell.syr.edu comp.databases.theory:37172 In article , heggland@idi.ntnu.no says... > In article <1141372781.078243.197630@e56g2000cwe.googlegroups.com>, > marshall.spight@gmail.com says... > > Jon Heggland wrote: > > > > > > As long as the type of a bunch of values is well-defined, there is > > > indeed no problem---indeed, that makes the two alternatives I outlined > > > equivalent. However, if any attribute is a set (or list), you probably > > > want (for convenience) to treat it as a single value of its constituent > > > type when it contains only one value, I.e. "Jon" = { "Jon" }. A language > > > that does this may exhibit undesirable behaviour in other places; I > > > believe SQL has trouble with table literals because of this. > > > > Can you say more about this? What kind of trouble? > > I think Hugh Darwen has written a piece on this. I'll try to dig it up. http://www.dbdebunk.com/page/page/2928212.htm discusses this, among other things (row types and user-defined types are also mentioned, in connection with the main point: NULLs). It's quite amusing, in a scary (for SQL users) way. It's mostly Darwen; Pascal-boycotters need not fear. The point I was referring to is in #3 in the list of SQL mistakes in Darwen's second reply; it may not be all that significant in our current discussion, though. -- Jon