Epistemic reasoning in logic programs

Although epistemic logic programming has an enhanced capacity to handle complex incomplete information reasoning and represent agents' epistemic behaviours, it embeds a significantly higher computational complexity than non-disjunctive and disjunctive answer set programming. In this paper, we investigate some important properties of epistemic logic programs. In particular, we show that Lee and Lifschitz's result on loop formulas for disjunctive logic programs can be extended to a special class of epistemic logic programs. We also study the polysize model property for epistemic logic programs. Based on these discoveries, we identify two non-trivial classes of epistemic logic programs whose consistency checking complexity is reduced from PSPACE-complete to NP-complete and Σ^P₂-complete respectively. We observe that many important applications on epistemic representation fall into these two classes of epistemic logic programs.