Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402280854.760d07b_at_posting.google.com...
>
> Given EyeColor = {red, brown, NOT_APPLICABLE}
> Given the table:
> Person EyeColor
> ------ --------------
> Mary NOT_APPLICABLE
> Bob NOT_APPLICABLE
>
> Then, Mary.EyeColor equals Bob.EyeColor leading an AI program to
> conclude that Mary and Bob have the same EyeColor.

What does it mean precisely to say that Mary and Bob have the same eye color? It means exactly this:

let color(X) be the color of an eye
let M be the set of Mary's eyes
let B be the set of Bob's eyes
for all m in M, for all b in B, color(m) = color(b)

Note that this works perfectly with having a N/A value in the eye color domain. So this hypothetical AI program will not be confused.

If, perchance, you are not comfortable with nullary logic, you might be tempted to introduce additional clauses to the above:

B is not empty
M is not empty

In which case, the question of whether Mary and Bob have the same color eyes is meaningless, in the same way that division by zero is meaningless, and again the hypothetical AI will not be confused.

(Unless this is one of those AIs like on Star Trek, where when you ask it to compute pi to the last digit it blows up.)

> This examplifies
> Date's conclusion: "3VL suffers from the very serious ("showstopper")
> problem that it does not match reality, that is results that are
> correct according to 3VL are sometimes incorrect in the real world".

If N/A is a value in the domain, then this is not an example of 3VL.

Marshall Received on Sun Feb 29 2004 - 00:55:48 CET