Re: Date's First Great Blunder
Date: 23 Apr 2004 22:49:16 -0700
> Not only are we not on the same page...
> I think we might be in different chapters.
I can see that operations on data can give us more than 2 values. We start at 2 values because it is the minimum needed to make distinctions and it is the simplest. More values should allow a db to model reality better, thus 5VL should be better than 4VL, and 6VL should be even better than 5VL, etc.
The core problem is not the number of values derivable from operations on data, but when a modelling system trys to represent missing info. RDM does this with NULLs initially and can subsequently patch them with special values. Now the db has data that doesn't match reality (ie there is no color in reality that is unknown, this only occurs in some modelling systems such as RDM). Operations on such data produces values that sometimes don't match reality even if the modelling system is 3VL or higher. This is why C. J. Date ends his chapter 20 with "NULLs and 3VL undermine the entire foundation of the relational model". Received on Sat Apr 24 2004 - 07:49:16 CEST