Re: SUPPORT FOR DECLARATIVE TRANSITION CONSTRAINTS

On 25 sep, 22:41, Brian <br..._at_selzer-software.com> wrote:
>
> The employee named paul c fills the position named toilet scrubber.
>
> Let's look at the information conveyed by this statement:
> 1. there is an employee named 'paul c.'
> 2. there is a position named 'toilet scrubber.'
> 3. the named employee fills the named position.
>
> Now, suppose that paul c's position changes from toilet scrubber to
> floor sweeper.
>
> Assuming that no other proposition references an employee named paul c
> or a position named toilet scrubber, doesn't the denial of
>
> (a) The employee named paul c fills the position named toilet
> scrubber.
>
> also deny that there is an employee named paul c and that there is a
> position named toilet scrubber?

LOFL. Who again was it that should go back to school and take a course in logic ?

EXISTS employee : employee(name) = 'paul c' && employee(position) = 'toilet scrubber' does indeed imply EXISTS employee : employee(name) = 'paul c' && EXISTS employee : employee(position) = 'toilet scrubber'. But note that the former and the latter are not equivalent, since the former conveys the extra information that the two properties apply to the very same person.

NOT EXISTS employee : employee(name) = 'paul c' && employee(position) = 'toilet scrubber' ===
FORALL employee : NOT(employee(name) = 'paul c' && employee(position) = 'toilet scrubber') ===
FORALL employee : employee(name) <> 'paul c' OR employee(position) <> 'toilet scrubber')

The denial of "(a) The employee named paul c fills the position named toilet scrubber." implies merely that if an employee is named paul c, then he is not a toilet scrubber, and also that if an employee is a toilet scrubber, then he is not named paul c.

So the answer to your question "doesn't the denial of ... also imply ..." is, "No, doesn't.". Received on Sun Sep 26 2010 - 11:16:11 CEST