Relating Defeasible and Normal Logic Programming through Transformation Properties

CARLOS IVÁN CHESÑEVAR; JÜRGEN DIX; FRIEDER STOLZENBURG; GUILLERMO SIMARI,

THEORETICAL COMPUTER SCIENCE

Lugar: Elsevier; Año: 2003 vol. 290 p. 499 - 529

0304-3975

This paper relates the Defeasible Logic Programming (DeLP) framework and its semantics SEMDeLP to classical logic programming frameworks. In DeLP, we distinguish between two di7erent 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 meaningof negative literals (not A) is different: they represent a kind of negation as failure, and thereby introduce defeasibility. Various semantics have been de;ned for NLP, notably the well-founded semantics (WFS) (van Gelder et al., Proceedings of the Seventh Symposium on Principles of Database Systems, 1988, pp. 221–230; J. ACM 38 (3) (1991) 620) and the stable semantics Stable (Gelfond and Lifschitz, Fifth Conference on Logic Programming, MIT Press, Cambridge, MA, 1988, pp. 1070–1080; Proceedings of the Seventh International Conference on Logical Programming, Jerusalem, MIT Press, Cambridge, MA, 1991, pp. 579–597). In this paper we consider the transformation properties for NLP introduced by Brass and Dix (J. Logic Programming 38(3) (1999) 167) and suitably adjusted for the DeLP framework. We show which transformation properties are satis;ed, thereby identifyingaspects in which NLP and DeLP differ. We contend that the transformation rules presented in this paper can help to gain a better understandingof the relationship of DeLP semantics with respect to more traditional logic programming approaches. As a byproduct, we obtain the result that DeLP is a proper extension of NLP.