Logic programming and software maintenance

The main objective of this short paper is to describe the relationship between software maintenance and logic programming (both declarative and procedural), and to show how ideas and methods from logic programming (in particular, methods invented by M. Gelfond) can be used in software maintenance. The material presented in this paper partly appeared in (Luqi and Cooke, 1995). The main difference is that (Luqi and Cooke, 1995) is aimed mainly at software engineers, so it only briefly touches on the software engineering problems, while describing in great detail the basics of logic programming. In contrast, in this paper, we assume that the corresponding logic programming notions are well known, but describe the corresponding software engineering applications in greater detail

Revising Nonmonotonic Belief Sets: The Case of Defeasible Logic

The revision and transformation of knowledge is widely recognized as a key issue in knowledge representation and reasoning. Reasons for the importance of this topic are the fact that intelligent systems are gradually developed and refined, and that often the environment of an intelligent system is not static but changes over time. Traditionally belief revision has been concerned with revising first order theories. Nonmonotonic reasoning provides rigorous techniques for reasoning with incomplete information. Until recently the dynamics of nonmonotonic reasoning approaches has attracted little attention. This paper studies the dynamics of defeasible logic, a simple and efficient form of nonmonotonic reasoning based on defeasible rules and priorities. We define revision and contraction operators and propose postulates. Our postulates try to follow the ideas of AGM belief revision as far as possible, but some AGM postulates clearly contradict the nonmonotonic nature of defeasible logic, as we explain. Finally we verify that the operators satisfy the postulates