{"type":"ScholarlyArticle","title":"Ordering Default Theories","authors":[{"name":"Chiaki Sakama","slug":"chiaki-sakama","given":"Chiaki","family":"Sakama","affiliation":""}],"abstract":"In first-order logic, a theory T 1 is considered stronger than another theory T 2 if every formula derived from T 2 is also derived from T1. Such an order relation is useful to know relative value between different theories. In the context of default logic, a theory contains default information as well as definite information. To order default theories, it is necessary to assess the information content of a default theory. To this end, we introduce a multi-valued interpretation of default theories based on a nine-valued bilattice. It distinguishes definite and credulous/skeptical default information derived from a theory, and is used for ordering default theories based on their information contents. The technique is also applied to order nonmonotonic logic programs. The results of this paper provide a method for comparing different default theories and have important application to learning nonmonotonic theories.","doi":null,"url":"https://ijcai.org/proceedings/2003/121","pdf":"https://ijcai.org/proceedings/2003/0121.pdf","markdown":"https://ijcai.org/proceedings/2003/121.md","bibtex":"https://ijcai.org/proceedings/2003/bibtex/121","volume":{"slug":"2003","title":"Proceedings of the Eighteenth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2003","url":"https://ijcai.org/proceedings/2003/","year":2003,"location":"Acapulco, Mexico","dates":"","editors":"Georg Gottlob","isbn":"","publisher":"International Joint Conferences on Artificial Intelligence","doi_prefix":""},"section":null,"track":"","number":121,"pages":{"first":839,"last":845},"keywords":[],"videos":[],"references":[],"license_note":"Copyright International Joint Conferences on Artificial Intelligence."}