Re: Demo: Modelling Cost of Travel Paths Between Towns

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0411171840.37842293_at_posting.google.com...
> > > Attempts to mask NULLs with unknowns or any other value, don't work
> > > (you must not have read my prior posts expounding the above point).
> >
> > Let's say the users have agreed to use the value 0 to indicate unknown
age.
>
> If two things have age 0, is it true or false that their ages are equal?

In one sense, they are equal, and in another we don't know. It depends on the exact question:

1. Do we know something about the age of these two people? Yes, we know that we don't know how old they are. We know the same thing about each of them, so what we know about each is equal.
2. Are these two the same age? We don't know, because a value of 0 (or -1) is known by the users (and the programmers) to mean "unknown".

If a NULL was used instead of 0/-1, the answer to the first question is also "We don't know," because NULLS have no meaning.

Same questions if the age of each is 30:

1. Yes, we know that they are both 30.
2. Yes, they are the same age.

Values are representations of facts, and the rules surrounding facts are determined by the people who use the facts, not by the universe. IOW, a particular value can mean different things to different people at different times in different places. This is the essence of what you have a hard time understanding. A symbolic representation does not always have the same connotation. Received on Thu Nov 18 2004 - 13:03:13 CET