Relating defeasible and normal logic programming through transformation properties

This paper relates the Defeasible Logic Programming (DeLP ) framework and its semantics SEMDeLP to classical logic programming frameworks. In DeLP we distinguish between two different sorts of rules: strict and defeasible rules. Negative literals ( A) in these rules are considered to represent classical negation. In contrast to this, in normal logic programming (NLP ), there is only one kind of rules, but the meaning of negative literals (notA) is different: they represent a kind of negation as failure, and thereby introduce defeasibility. Various semantics have been defined for NLP , notably the well-founded semantics WFS and the stable semantics Stable. In this paper we consider the transformation properties for NLP introduced by Brass and Dix and suitably adjusted for the DeLP framework. We show which transformation properties are satisfied, thereby identifying aspects in which NLP and DeLP differ. We contend that the transformation rules presented in this paper can help to gain a better understanding of the relationship of DeLP semantics with respect to more traditional logic programming approaches. As a byproduct, we get that DeLP is a proper extension of NLP .