Publications on Belief Revision

David Billington, Grigoris Antoniou, Guido Governatori, and Michael J. Maher.
Revising nonmonotonic belief sets: The case of defeasible logic. In Wolfram Burgard, Thomas Christaller, and Armin B. Cremers, editors, KI-99: Advances in Artificial Intelligence, volume 1701 of LNAI, pages 101-112, Berlin, 1999. Springer-Verlag, Copyright © 1999 Springer-Verlag.
Abstract: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, propose postulates motivated by the form or the intuition of the AGM postulates for classical belief revision, and verify that the operators satisfy the postulates.
 
Guido Boella, Guido Governatori, Antonino Rotolo, and Leendert van der Torre.
A formal study on legal compliance and interpretation. In Thomas Meyer and Eugenia Ternovska, editors, 13 International Workshop on Non-Monotonic Reasoning (NMR 2010). CEUR Workshop Proceedings, 2010.
Abstract: This paper proposes a logical framework to capture the norm change power and the limitations of the judicial system in revising the set of constitutive rules defining the concepts on which the applicability of norms is based. In particular, we reconstruct the legal arguments leading to an extensive or re- strictive interpretation of norms.
 
Guido Boella, Guido Governatori, Antonino Rotolo, and Leendert van der Torre.
Lex minus dixit quam voluit, lex magis dixit quam voluit: A formal study on legal compliance and interpretation. In P. Casanovas, U. Pagallo, G. Ajani, and G. Sartor, editors, AI approaches to the complexity of legal systems, LNAI, Berlin, 2010. Springer, Copyright © 2010 Springer.
Abstract: This paper argues in favour of the necessity of dynamically restricting and expanding the applicability of norms regulating computer systems like multiagent systems, in situations where the compliance to the norm does not achieve the purpose of the norm. We propose a logical framework which distinguishes between constitutive and regulative norms and captures the norm change power and at the same time the limitations of the judicial system in dynamically revising the set of constitutive rules defining the concepts on which the applicability of norms is based. In particular, the framework is used to reconstruct some interpretive arguments described in legal theory such as those corresponding to the Roman maxims lex minus dixit quam voluit and lex magis dixit quam voluit. The logical framework is based on an extension of defeasible logic.
 
Guido Boella, Guido Governatori, Antonino Rotolo, and Leendert van der Torre.
A logical understanding of legal interpretation. In Proceedings of KR 2010. AAAI, 2010.
Abstract: If compliance with a norm does not achieve its purpose, then its applicability must dynamically be restricted or expanded. Legal interpretation is a mechanism from law allowing norms to be adapted to unforeseen situations. We model this mechanism for norms regulating computer systems by representing the purpose of norms by social goals and by revising the constitutive rules defining the applicability of norms. We illustrate the interpretation mechanism by examples.
 
Paolo Di Giusto and Guido Governatori.
Analytic modal revision for multi-agent systems. In Pedro Barahona and José Júlio Alferes, editors, Progress in Artificial Intelligence, volume 1695 of LNAI, pages 282-296, Berlin, 1999. Springer-Verlag, Copyright © 1999 Springer-Verlag.
Abstract:We present two models of hierarchical structured multi-agents, and we describe how to obtain a modal knowledge base from distributed sources. We then propose a computationally oriented revision procedure for modal knowledge bases. This procedure is based on a labelled tableaux calculi supplemented with a formalism to record the dependencies of the formulae. The dependencies are then used to reconstruct the minimal inconsistent sets, and the sub-formulae responsible for the inconsistencies are revised according to well-defined chains of modal functions.
 
Paolo Di Giusto and Guido Governatori.
Modifying is better than deleting: A new approach to base revision. In Evelina Lamma and Paola Mello, editors, AI*IA 99, pages 145-154, Bologna, 1999. Pitagora.
Abstract:We present three approaches to belief base revision, which are examined also in the case in which the sentences in the base are partitioned between those which can and those which cannot be changed; the approaches are shown to be semantically equivalent. A new approach is then presented, based on the modification of individual rules, instead of deletion. The resulting base is semantically equivalent to that generated by the other approaches, in the sense that it has the same models, but the rule part alone has less models, that is, is subjected to a smaller change.
 
Paolo Di Giusto and Guido Governatori.
A new approach to base revision. In Pedro Barahona and José Júlio Alferes, editors, Progress in Artificial Intelligence, volume 1695 of LNAI, pages 327-341, Berlin, 1999. Springer-Verlag, Copyright © 1999 Springer-Verlag.
Abstract:We present three approaches to revision of belief bases, which are also examined in the case in which the sentences in the base are partitioned between those which can and those which cannot be changed; the approaches are shown to be semantically equivalent. A new approach is then presented, based on the modification of individual rules, instead of deletion. The resulting base is semantically equivalent to that generated by the other approaches, in the sense that it has the same models, but the rule part alone has fewer models, that is, is subjected to a smaller change.
 
Guido Governatori, Francesco Olivieri, Simone Scannapieco, and Matteo Cristani.
Superiority based revision of defeasible theories. In Mike Dean, John Hall, Antonino Rotolo, and Said Tabet, editors, RuleML 2010: 4th International Web Rule Symposium, number 6403 in LNCS, pages 104-118, Berlin, 2010. Springer. Copyrigth © 2010 Springer.
Abstract: We propose a systematic investigation on how to modify a preference relation in a defeasible logic theory to change the conclusions of the theory itself. We argue that the approach we adopt is applicable to legal reasoning, where users, in general, cannot change facts and rules, but can propose their preferences about the relative strength of the rules. We provide a comprehensive study of the possible combinatorial cases and we identify and analyse the cases where the revision process is successful.
 
Guido Governatori and Antonino Rotolo.
Changing legal systems: Abrogation and annulment. Part I: Revision of defeasible theories. In Ron van der Meyden and Leon van der Torre, editors, 9th International Conference on Deontic Logic in Computer Science (DEON2008), Lecture Notes in Computer Science. Springer, 2008. Copyright © 2008 Springer.
Abstract: In this paper we investigate how to model legal abrogation and annulment in Defeasible Logic. We examine some options that embed in this setting, and similar rule-based systems, ideas from belief and base revision. In both cases, our conclusion is negative, which suggests to adopt a different logical model.
 
Guido Governatori and Antonino Rotolo.
Changing legal systems: Abrogation and annulment. Part II: Temporalised defeasible logic. In Guido Boella, Harko Verhagen, and Muindhar Singh, editors, Proceedings of Normative Multi Agent Systems (NorMAS 2008, Luxembourg 15-16 July 2008.
Abstract: In this paper we propose a temporal extension of Defeasible Logic to model legal modifications, such as abrogation and annulment. Hence, this framework overcomes the difficulty, discussed elsewhere \cite{deon-part1}, of capturing these modification types using belief and base revision.
 
Guido Governatori and Antonino Rotolo.
Changing legal systems: legal abrogations and annulments in defeasible logic. Logic Journal of IGPL, 18 no. 1 pp. 157-194, 2009. Copyright © 2010 Oxford University Press.
Abstract: In this paper we investigate how to represent and reason about legal abrogations and annulments in Defeasible Logic. We examine some options that embed in this setting, and in similar rule-based systems, ideas from belief and base revision. In both cases, our conclusion is negative, which suggests to adopt a different logical model. This model expresses temporal aspects of legal rules, and distinguishes between two main timelines, one internal to a given temporal version of the legal system, and another relative to how the legal system evolves over time. Accordingly, we propose a temporal extension of Defeasible Logic suitable to express this model and to capture abrogation and annulment. We show that the proposed framework overcomes the difficulties discussed in regard to belief and base revision, and is sufficiently flexible to represent many of the subtleties characterizing legal abrogations and annulments.