Re: ISSUE: DAML+OIL semantics is too weak

[...]

> > I also use modus tollens (actually resolution)
> > quite a lot inside the engine, but it's not safe
> > I think as outside (non-closed world) evidence.
> >
> > --
> > Jos
>
> How is modus tollens unsafe?

I think the trouble starts with your rule
  ?x a ?y, ?x a [owl:complementOf :y] -> FALSE

We can't assert such a rule with a conclusion
that is FALSE (as it is not a Horn clause).
We would rather write a rule like
  { :rule16c1 . ?x a ?y . ?x a ?z . ?y owl:complementOf ?z }
  log:implies { ?x :inconsistentWith owl:complementOf } .

so have the inconsistency detected explicitly
and that would not mean discharging assumptions.

> peter

--
Jos