RE: AW: Safe Execution of Recursive Axioms + English

> 
> > One example is existential quantification, which you can
> > only do in one directions of implication, since existentials
> > in the head are generally unavailable in Datalog. Another
> > example is negation, which has different semantics (incompatible
> > with FOL negation).
Existential quantifications are generally unavailable in Datalog but it
does not mean that one can not answer some class of queries
(conjunctive, for example) using datalog program.
The rewriting method can be applied in this domain to get datalog
program answering CQ over ontologies with existential variables in the
right.
> EXPTIME-hard. So, again, I don't understand what are you really doing.
>