Re: Does Codd's view of a relational database differ from that of Date & Darwin? [M.Gittens]
Date: 10 Jun 2005 10:30:11 -0700
My comment on this thread would be that the problems here arise not from missing information per se, nor from the empty set, special values, or whatever. The problems arise from 3VL. Once you introduce an unknown value, you can't say anything about anything. Is x = UNKNOWN? It might be, it might not; you can't tell. What about the sum of a set of numbers and an UNKNOWN? Nothing can be said about it.
Marshall Received on Fri Jun 10 2005 - 19:30:11 CEST