Re: 3vl 2vl and NULL

David Cressey wrote:
> There is a 3VL whose values are [TRUE,FALSE,MEANINGLESS] when a formula
> comes up MEANINGLESS, it means that it is not a "well formed formula" or
> WFF. The definition of a WFF is outside this discussion. But an assertion
> of MEANINGLESS is a denial of TRUE and FALSE.

Hi David, am I correct in saying that in a domain like {1,2,3,null} something like 1<null is an example of one of these non-WFF? With an ordering like < db's always assume that the domain is totally orderered, but with the inclusion of null we now have a partially ordered set, as null is logically incomparable to anything else in the set - it is this incomparability that means non-WFF can emerge. So normally if a mathematician is working with a theory and comes across a non-WFF it is just thrown out as not part of the theory. But with Codd's RM we are not doing so, we are trying to accomodate them. Is there any justification for this, or is it mathematically incorrect to do so?

Essentially I'm asking is that is there a mathematical reason here why the incorporation of null's is non-sensical, or is it okay to layer a {TRUE, FALSE, MEANINGLESS} logic over a theory with non-WFF? Received on Mon Dec 12 2005 - 14:51:25 CET