Published online by Cambridge University Press: 05 May 2020
Epistemic logic programs constitute an extension of the stable model semantics to deal with new constructs called subjective literals. Informally speaking, a subjective literal allows checking whether some objective literal is true in all or some stable models. As it can be imagined, the associated semantics has proved to be non-trivial, since the truth of subjective literals may interfere with the set of stable models it is supposed to query. As a consequence, no clear agreement has been reached and different semantic proposals have been made in the literature. Unfortunately, comparison among these proposals has been limited to a study of their effect on individual examples, rather than identifying general properties to be checked. In this paper, we propose an extension of the well-known splitting property for logic programs to the epistemic case. We formally define when an arbitrary semantics satisfies the epistemic splitting property and examine some of the consequences that can be derived from that, including its relation to conformant planning and to epistemic constraints. Interestingly, we prove (through counterexamples) that most of the existing approaches fail to fulfill the epistemic splitting property, except the original semantics proposed by Gelfond 1991 and a recent proposal by the authors, called Founded Autoepistemic Equilibrium Logic.
This is an extended version of a conference paper presented at the Fifteenth International Conference on Logic Programming and Nonmonotonic Reasoning, Philadelphia, PA, USA, June 3–7, 2019, where it received a best technical paper award (Cabalar et al. 2019b) An earlier version was also presented at the Seventeenth International Workshop on Non-monotonic Reasoning (Cabalar et al. 2018). This work was partially supported by MINECO, Spain, grant TIC2017-84453-P, Xunta de Galicia, Spain (GPC ED431B 2019/03). The second author was funded by the Centre International de Mathématiques et d’Informatique de Toulouse (CIMI) through contract ANR-11-LABEX-0040-CIMI within the program ANR-11-IDEX-0002-02 and the Alexander von Humboldt Foundation. We are thankful to Michael Gelfond, Richard Watson, Patrick T. Kahl, and the anonymous reviewers of the Seventeenth International Workshop on Non-monotonic Reasoning (NMR’18) and the Fifteenth International Conference on Logic Programming and Nonmonotonic Reasoning (LPNMR’19) where preliminary versions of this work were presented, for their comments and suggestions that have helped improving the paper substantially. We are also thankful to the organizers of LPNMR’19 for their support in preparing this extended version.