A Comparison of Two Approaches to Splitting Default Theories

Default logic is computationally expensive. One of the most promising ways of easing this problem and developing powerful implementations is to split a default theory into smaller parts and compute extensions in a modular, "local" way. This paper compares two recent approaches, Turner's splitting and Cholewinski's stratification. It shows that the approaches are closely related -- in fact the former can be viewed as a special case of the latter. 1 Introduction Default logic (Reiter 1980) is one of the most prominent approaches of nonmonotonic reasoning, since it provides a formal theory of reasoning based on default rules. One of the main problems with its applicability is that it is computationally harder than classical logic (Marek and Truszczynski 1993, Gottlob 1992), which makes the implementation of powerful systems difficult. A possible solution to this problem might be to split the available knowledge into smaller parts, and to apply default reasoning in a local way. This idea..