Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cimshop!davidm From: cimshop!davidm@uunet.UU.NET (David S. Masterson) Newsgroups: comp.databases Subject: Re: Stoopid questions - One down, one to go Message-ID: Date: 30 Sep 90 09:27:48 GMT References: Sender: davidm@cimshop.UUCP Distribution: comp Organization: Consilium Inc., Mountain View, California. Lines: 26 In-reply-to: Chuck.Phillips@FtCollins.NCR.COM's message of 26 Sep 90 10:15:18 GMT In article Chuck.Phillips@FtCollins.NCR.COM (Chuck.Phillips) writes: Continuing the "value unknown" thread... TRUE OR TRUE = TRUE TRUE OR FALSE = TRUE ergo, in three-value boolean algebra: TRUE OR UNKNOWN = TRUE ...but in relational algebra TRUE OR UNKNOWN = UNKNOWN (!) This is not what I remember seeing in Codd's book. Certain conclusions have to occur in order to maintain transitive closure. I think relational algebra goes along with boolean algebra. Unless this is some mix of three and four valued logic?!? -- ==================================================================== David Masterson Consilium, Inc. uunet!cimshop!davidm Mtn. View, CA 94043 ==================================================================== "If someone thinks they know what I said, then I didn't say it!"