And I thought that Ernest was putting it on a bit thick when he was writing about the "background [...] in philosophy" ;-)
Well, propositional logic and predicate logic are formal systems, and assumptions there are as they must be to remain consistent, in a purely abstract way. On the other hand, Jess (and all other systems) are used in a pragmatic context where it makes sense to assume that the system has full knowledge, and absence of a fact (from the domains the system is meant to cover) means that it is false. But - and that's important - this assumption is only an assumption that just helps us in getting smartly along, most of the time, by accepting what the closed-world of our data-base-cum-application spews out at us. Luckily, we can occasionally break through this assumption. The other day, at some gate in Munich airport, I was trying to board a connection flight to Madrid, when the young lady there told me that I didn't have a seat on this plane, because I hadn't checked in. Well, I had, back home, before the first leg. After suffering a little while from the closed-world assumption, and after confirming that I had indeed been on the first flight, that I was indeed there in the flesh, and that I really did want to go to Madrid, she gave me my boarding pass, I gave her a blackcurrant candy, and we parted as friends. Nevertheless, Samson's contention is certainly justified, and I'll add some suitable paragraph (after waiting a little while for other comments.) -W On Tue, Feb 10, 2009 at 6:57 PM, Samson Tu <[email protected]> wrote: > The article should have mentioned that predicate logic uses the "open-world > assumption" while JESS has negation-as-failure semantics. It's a fundamental > difference between predicate logic and Jess - predicate logic is monotonic > while JESS is not. Statements that are true in Jess may not be true in > predicate logic. > > Samson > > -------------------------------------------------------------------- To unsubscribe, send the words 'unsubscribe jess-users [email protected]' in the BODY of a message to [email protected], NOT to the list (use your own address!) List problems? Notify [email protected]. --------------------------------------------------------------------
