Path: newssvr20.news.prodigy.com!newsmst01.news.prodigy.com!prodigy.com!postmaster.news.prodigy.com!newssvr33.news.prodigy.com.POSTED!b137e2aa!not-for-mail From: "Eric Kaun" Newsgroups: comp.databases.theory References: <4b45d3ad.0402231444.2f77c935@posting.google.com> <4b45d3ad.0402241308.680a4901@posting.google.com> <4b45d3ad.0402251221.1478fb07@posting.google.com> <2ee%b.57781$Xp.288048@attbi_s54> <4b45d3ad.0402261256.783f8bd2@posting.google.com> <5BO%b.18056$2%4.355@newssvr31.news.prodigy.com> <4b45d3ad.0402281221.431f280@posting.google.com> Subject: Re: object algebra Lines: 20 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Message-ID: NNTP-Posting-Host: 216.151.76.34 X-Complaints-To: abuse@prodigy.net X-Trace: newssvr33.news.prodigy.com 1078320304 ST000 216.151.76.34 (Wed, 03 Mar 2004 08:25:04 EST) NNTP-Posting-Date: Wed, 03 Mar 2004 08:25:04 EST Organization: SBC http://yahoo.sbc.com X-UserInfo1: FKPO@MC@OHWERV\[@BCDN_HAQB^H@IPDLXUNNHPIMASJETAANVW[AKWZE\]^XQWIGNE_[EBL@^_\^JOCQ^RSNVLGTFTKHTXHHP[NB\_C@\SD@EP_[KCXX__AGDDEKGFNB\ZOKLRNCY_CGG[RHT_UN@C_BSY\G__IJIX_PLSA[CCFAULEY\FL\VLGANTQQ]FN Date: Wed, 03 Mar 2004 13:25:04 GMT Xref: newssvr20.news.prodigy.com comp.databases.theory:24350 "Neo" wrote in message news:4b45d3ad.0402281221.431f280@posting.google.com... > > The above isn't a "patch for" nulls. What does "weaker relationship" mean, > > though? I have no idea how to address that one. > > Given EyeColor = {red, brown, N/A} and the table: > Person EyeColor > ------ -------- > John N/A > Mary N/A > > A query to find persons with equal eyeColor returns: John & Mary. Again, when defining a domain (which can be tricky!) you define the operations over it. You sometimes need to do that when representations (POSSREPS) are different, though I'm oversimplifying this whole thing in the interest of brevity.