why not negation by fixpoint?
There is a fixpoint semantics for DATALOG programs with negation that is a natural generalization of the standard semantics for DATALOG programs without negation. We show that, unfortunately, several compelling complexity-theoretic obstacles rule out its efficient implementation. As an alternative, we propose Inflationary DATALOG, an efficiently implementable semantics for negation, based on inflationary fixpoints
semantic datalog program general standardization efficiency implementation complexity