Path: utzoo!attcan!uunet!ncrlnk!ncr-mpd!Chuck.Phillips From: Chuck.Phillips@FtCollins.NCR.COM (Chuck.Phillips) Newsgroups: comp.databases Subject: Re: Outerjoin implementation? (4-valued question) Message-ID: Date: 8 Oct 90 08:09:44 GMT References: <5803@plains.NoDak.edu> <30203@netnews.upenn.edu> <152008@felix.UUCP> <30712@netnews. Sender: uucp@ncr-mpd.FtCollins Distribution: comp Organization: NCR Microelectronics, Ft. Collins, CO Lines: 32 In-reply-to: aaron@grad2.cis.upenn.edu's message of 7 Oct 90 20:23:37 GMT Just a nit: >>>>> On 7 Oct 90 20:23:37 GMT, aaron@grad2.cis.upenn.edu (Aaron Watters) said: Aaron> unknown means `this may be true or false or error, but we don't Aaron> know which.' Aaron> error means `this can't have any truth value' So far so good. Aaron> -- in the example above ["the king of North America is bald"] Aaron> because any truth value requires the existence of someone who Aaron> (last I heard) doesn't exist. Clairification: A statement requiring the existance of the non-existant to be true, is simply false, not an error. However, a domain violation _is_ an error. (e.g. "I am green years old.") If "king" is an out-of-band attribute, then the statement is an error; if "king" is within the defined domain, then the statement is simply false. Hope this helps, Chuck Phillips MS440 NCR Microelectronics chuck.phillips%ftcollins.ncr.com 2001 Danfield Ct. Ft. Collins, CO. 80525 ...uunet!ncrlnk!ncr-mpd!bach!chuckp -- Chuck Phillips MS440 NCR Microelectronics chuck.phillips%ftcollins.ncr.com 2001 Danfield Ct. Ft. Collins, CO. 80525 ...uunet!ncrlnk!ncr-mpd!bach!chuckp