Publications on Non-monotonic Reasoning

Grigoris Antoniou, David Billington, Guido Governatori, and Michael J. Maher.
A flexible framework for defeasible logics. In Proc. American National Conference on Artificial Intelligence (AAAI-2000), pages 401-405, Menlo Park, CA, 2000. AAAI/MIT Press, Copyright © 2000 AAAI, American Association for Artificial Intelligence.
Abstract:Logics for knowledge representation suffer from over-specialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In general, such an approach results in a very difficult problem of combination. However, if we can choose the logics from a uniform framework then the problem of combining them is greatly simplified. In this paper, we develop such a framework for defeasible logics. It supports all defeasible logics that satisfy a strong negation principle. We use logic meta-programs as the basis for the framework.
 
Grigoris Antoniou, David Billington, Guido Governatori, and Michael J. Maher.
A flexible framework for defeasible logics. In Proceeding of the 9th$ Workshop on Non-Monotonic Reasoning, 2000.
Abstract:Logics for knowledge representation suffer from over-specialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In general, such an approach results in a very difficult problem of combination. However, if we can choose the logics from a uniform framework then the problem of combining them is greatly simplified. In this paper, we develop such a framework for defeasible logics. It supports all defeasible logics that satisfy a strong negation principle. We use logic meta-programs as the basis for the framework.
 
Grigoris Antoniou, David Billington, Guido Governatori, and Michael J. Maher.
Representation results for defeasible logic. ACM Transactions on Computational Logic, 2 no. 2 pp. 255-287, April 2001., Copyright © 2001 ACM.
Abstract:The importance of transformations and normal forms in logic programming, and generally in computer science, is well documented. This paper investigates transformations and normal forms in the context of Defeasible Logic, a simple but efficient formalism for nonmonotonic reasoning based on rules and priorities. The transformations described in this paper have two main benefits: on one hand they can be used as a theoretical tool that leads to a deeper understanding of the formalism, and on the other hand they have been used in the development of an efficient implementation of defeasible logic.
 
Grigoris Antoniou, David Billington, Guido Governatori and Micheal J. Maher.
Embedding Defeasible Logic into Logic Programming Theory and Practice of Logic Programming, 6, 6, pp 803-835. Copyright © Cambridge University Press.
Abstract: Defeasible reasoning is a simple but efficient approach to nonmonotonic reasoning that has recently attracted considerable interest and that has found various applications. Defeasible logic and its variants are an important family of defeasible reasoning methods. So far no relationship has been established between defeasible logic and mainstream nonmonotonic reasoning approaches. In this paper we establish close links to known semantics of logic programs. In particular, we give a translation of a defeasible theory D into a meta-program P(D). We show that under a condition of decisiveness, the defeasible consequences of D correspond exactly to the sceptical conclusions of P(D) under the stable model semantics. Without decisiveness, the result holds only in one direction (all defeasible consequences of D are included in all stable models of P(D)). If we wish a complete embedding for the general case, we need to use the Kunen semantics of P(D), instead.
 
Grigoris Antoniou, David Billington, Guido Governatori, Michael J. Maher, and Andrew Rock.
A family of defeasible reasoning logics and its implementation. In Werner Horn, editor, ECAI 2000. Proceedings of the 14th European Conference on Artificial Intelligence, pages 459-463, Amsterdam, 2000. IOS Press.
Abstract:Defeasible reasoning is a direction in nonmonotonic reasoning that is based on the use of rules that may be defeated by other rules. It is a simple, but often more efficient approach than other nonmonotonic reasoning systems. This paper presents a family of defeasible reasoning formalisms built around Nute's defeasible logic. We describe the motivations of these formalisms and derive some basic properties and interrelationships. We also describe a query answering system that supports these formalisms and is available on the World Wide Web.
 
Grigoris Antoniou, Michael J. Maher, David Billington, and Guido Governatori.
Comparison of sceptical naf-free logic programming approaches. In M. Gelfond, N. Leone, and G. Pfeifer, editors, Logic Programming and Non-monotonic Reasoning, volume 1730 of LNAI, pages 347-356, Berlin, 1999. Springer-Verlag, Copyright © 1999 Springer-Verlag.
Abstract:Recently there has been increased interest in logic programming-based default reasoning approaches which are not using negation-as-failure in their object language. Instead, default reasoning is modelled by rules and a priority relation among them. Historically the first logic in this class was Defeasible Logic. In this paer we will study its relationship to other approaches which also rely on the idea of using logic rules and priorities. In particular we will study sceptical LPwNF, courteous logic programs, and priority logic.
 
Alberto Artosi, Paola Cattabriga, and Guido Governatori.
A modal computational framework for default reasoning. In Gerhard Brewka, Christopher Habel, and Bernhard Nebel, editors, Proceedings of KI-97, volume 1303 of LNAI, pages 373-376, Berlin, 1997. Springer-Verlag.
 
Alberto Artosi and Guido Governatori.
Modal tableaux for nonmonotonic reasoning. In Vito Michele Abrusci, Carlo Cellucci, Roberto Cordeschi, and Vincenzo Fano, editors, Prospettive della logica e della filosofia della scienza, pages 203-213, Pisa, 1998. ETS.
 
Alberto Artosi and Guido Governatori.
A tableaux methodology for deontic conditional logics. In ΔEON'98, 4th International Workshop on Deontic Logic in Computer Science, pages 65-81, Bologna, 1998. CIRFID.
Abstract:In this paper we present a theorem proving methodology for a restricted but significant fragment of the conditional language made up of (boolean combinations of) conditional statements with unnested antecedents. The method is based on the possible world semantics for conditional logics. The label formalism introduced in \cite{cade,jelia} to account for the semantics of normal modal logics is easily adapted to the semantics of conditional logics by simply indexing labels with formulas. The inference rules are provided by the propositional system KE+ - a tableau-like analytic proof system devised to be used both as a refutation and a direct method of proof - enlarged with suitable elimination rules for the conditional connective. The theorem proving methodology we are going to present can be viewed as a first step towards developing an appropriate algorithmic framework for several conditional logics for (defeasible) conditional obligation.
 
Alberto Artosi, Guido Governatori, and Antonino Rotolo.
A labelled tableau calculus for nonmonotonic (cumulative) consequence relations. In Roy Dyckhoff, editor, Automated Reasoning with Analytic Tableaux and Related Methods, volume 1847 of LNAI, pages 82-97, Berlin, 2000. Springer-Verlag, Copyright © 2000 Springer-Verlag.
Abstract:In this paper we present a labelled proof method for computing nonmonotonic consequence relations in a conditional logic setting. The method is based on the usual possible world semantics for conditional logic. The label formalism KEM, introduced to account for the semantics of normal modal logics, is easily adapted to the semantics of conditional logic by simply indexing labels with formulas. The inference rules are provided by the propositional system KE+ - a tableau-like analytic proof system devised to be used both as a refutation and a direct method of proof - enlarged with suitable elimination rules for the conditional connective. The resulting algorithmic framework is able to compute cumulative consequence relations in so far as they can be expressed as conditional implications.
 
Alberto Artosi, Guido Governatori, and Antonino Rotolo.
Labelled tableaux for non-monotonic reasoning: Cumulative consequence relations. Journal of Logic and Computation, 12 no. ? pp. ?, ? 2002. Copyright © 2002, Oxford University Press.
Abstract:In this paper we present a labelled proof method for computing nonmonotonic consequence relations in a conditional logic setting. The method exploits the strong connection between these deductive relations and conditional logics, and it is based on the usual possible world semantics devised for the latter. The label formalism KEM, introduced to account for the semantics of normal modal logics, is easily adapted to the semantics of conditional logic by simply indexing labels with formulas. The basic inference rules are provided by the propositional system KE+ - a tableau-like analytic proof system devised to be used both as a refutation method and a direct method of proof - that is the classical core of KEM which is thus enlarged with suitable elimination rules for the conditional connective. The resulting algorithmic framework is able to compute cumulative consequence relations in so far as they can be expressed as conditional implications.
 
Alberto Artosi, Guido Governatori, and Giovanni Sartor.
Towards a computational treatment of deontic defeasibility. In Mark Brown and José Carmo, editors, Deontic Logic Agency and Normative Systems, Workshop on Computing, pages 27-46, Berlin, 1996. Springer-Verlag, Copyright © 1996 Springer-Verlag.
Abstract:In this paper we describe an algorithmic framework for a multi-modal logic arising from the combination of the system of modal (epistemic) logic devised by Meyer and van der Hoek for dealing with nonmonotonic reasoning with a deontic logic of the Jones and Pörn-type. The idea behind this (somewhat eclectic) formal set-up is to have a modal framework expressive enough to model certain kinds of deontic defeasibility, in particular by taking into account preferences on norms. The appropriate inference mechanism is provided by a tableau-like modal theorem proving system which supports a proof method closely related to the semantics of modal operators. We argue that this system is particularly well-suited for mechanizing nonmonotonic forms of inference in a monotonic multi-modal setting.
 
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.
 
David Billington, Grigoris Antoniou, Guido Governatori, and Michael J. Maher.
An inclusion theorem for defeasible logic. ACM Transactions in Computational Logic.
Abstract: Defeasible reasoning is a computationally simple nonmonotonic reasoning approach that has attracted significant theoretical and practical attention. It comprises a family of logics that capture different intuitions, among them ambiguity propagation versus ambiguity blocking, and the adoption or rejection of team defeat. This paper provides a compact presentation of the defeasible logic variants, and derives an Inclusion Theorem which shows that different notions of provability in defeasible logic form a chain of levels of proof.
 
Jenny Eriksson Lundström, Guido Governatori, Subhasis Thakur, and Vineet Padmanabhan.
An asymmetric protocol for argumentation games in defeasible logic. In Aditya Ghose and Guido Governatori, editors, 10 Pacific Rim International Workshop on Multi-Agents, LNAI 5044. Springer, 2008 Copyright © 2008 Springer.
Abstract: Agent interactions where the agents hold conflicting goals could be modelled as adversarial argumentation games. In many real-life situations (e.g., criminal litigation, consumer legislation), due to ethical, moral or other principles governing interaction, the burden of proof, i.e., which party is to lose if the evidence is balanced, is a priori fixed to one of the parties. Analogously, when resolving disputes in a heterogeneous agent-system the unequal importance of different agents for carrying out the overall system goal need to be accounted for. In this paper we present an asymmetric protocol for an adversarial argumentation game in Defeasible Logic, suggesting Defeasible Logic as a general representation formalism for argumentation games modelling agent interactions.
 
Guido Governatori.
Defeasible description logic. In Grigoris Antoniou and Harold Boley, editors, Rules and Rule Markup Languages for the Semantic Web: Third International Workshop, RuleML 2004, number 3323 in LNCS, pages 98-112, Berlin, 8 November 2004. Springer-Verlag Copyright © 2004, Springer. The original pubblication is available at www.springerlink.com
Abstract:We propose to extend description logic with defeasible rules, and to use the inferential mechanism of defeasible logic to reason with description logic constructors.
 
Guido Governatori and Michael J. Maher.
An argumentation-theoretic characterization of defeasible logic. In Werner Horn, editor, ECAI 2000. Proceedings of the 14th European Conference on Artificial Intelligence, pages 469-474, Amsterdam, 2000. IOS Press.
Abstract:Defeasible logic is an efficient non-monotonic logic that is defined only proof-theoretically. It has potential application in some legal domains. We present here an argumentation semantics for defeasible logic that will be useful in these applications. Our development differs at several points from existing argumentation frameworks since there are several features of defeasible logic that have not been addressed in the literature.
 
Guido Governatori, Michael J. Maher, Grigoris Antoniou, and David Billington.
Argumentation semantics for defeasible logics. In Riichiro Mizoguchi and John Slaney, editors, PRICAI 2000: Topics in Artificial Intelligence, volume 1886 of LNAI, pages 27-37, Berlin, 2000. Springer-Verlag, Copyright © 2000 Springer-Verlag.
Abstract:Defeasible logic is an efficient non-monotonic logic that is defined only proof-theoretically. It has potential application in some legal domains. We present here argumentation semantics for variants of defeasible logic that will be useful in these applications.
 
Guido Governatori, Michael J. Maher, David Billington, and Grigoris Antoniou.
Argumentation semantics for defeasible logics. Journal of Logic and Computation, 14, no. 5, pp. 675-702, 2004. Copyright © 2004 Oxford University Press.

Abstract:Defeasible reasoning is a simple but efficient rule-based approach to nonmonotonic reasoning. It has powerful implementations and shows promise to be applied in the areas of legal reasoning and the modeling of business rules. This paper establishes significant links between defeasible reasoning and argumentation. In particular, Dung-like argumentation semantics is provided for two key defeasible logics, of which one is ambiguity propagating and the other ambiguity blocking. There are several reasons for the significance of this work: (a) establishing links between formal systems leads to a better understanding and cross-fertilization, in particular our work sheds light on the argumentation-theoretic features of defeasible logic; (b) we provide the first ambiguity blocking Dung-like argumentation system; (c) defeasible reasoning may provide an efficient implementation platform for systems of argumentation; and (d) argumentation-based semantics support a deeper understanding of defeasible reasoning, especially in the context of the intended applications.
 
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 Vineet Padmanabhan.
A defeasible logic of policy-based intention. In Tamás D. Gedeon and Lance Chun Che Fung, editors, AI 2003: Advances in Artificial Intelligence, volume 2903 of LNAI, pages 414-426, Springer-Verlag, Berlin, 2003. Copyright © 2003 Springer-Verlag.
Abstract:Most of the theories on formalising intention interpret it as a unary modal operator in Kripkean semantics, which gives it a monotonic look. We argue that policy-based intentions exhibit non-monotonic behaviour which could be captured through a non-monotonic system like defeasible logic. To this end we outline a defeasible logic of intention. The proposed technique alleviates most of the problems related to logical omniscience. The proof theory given shows how our approach helps in the maintenance of intention-consistency in agent systems like BDI.
 
Guido Governatori and Antonino Rotolo.
A Gentzen system for reasoning with contrary-to-duty obligations. a preliminary study. In Andrew J.I. Jones and John Horty, editors, $\Delta$eon'02, pages 97-116, London, May 2002. Imperial College.
Abstract:In this paper we present a Gentzen system for reasoning with contrary-to-duty obligations. The intuition behind the system is that a contrary-to-duty is a special kind of normative exception. The logical machinery to formalize this idea is taken from substructural logics and it is based on the definition of a new non-classical connective capturing the notion of reparational obligation. Then the system is tested against well-known contrary-to-duty paradoxes.
 
Guido Governatori and Antonino Rotolo.
A computational framework for non-monotonic agency, institutionalised power and multi-agent systems. In Daniéle Bourcier, editor, Legal Knowledge and Inforamtion Systems, volume 106 of Frontieres in Artificial Intelligence and Applications, pages 151-152, IOS Press, Amsterdam, 2003.
 
Guido Governatori and Antonino Rotolo.
A defeasible logic of institutional agency. In Gerhard Brewka and Pavlos Peppas, editors, NRAC'03, pages 97-104, Acapulco, Mexico, 10-11 August 2003. IJCAI.
Abstract:A non-monotonic logic of institutional agency is defined combining a computationally oriented non-monotonic system (Defeasible Logic) and intensional notions of agency.
 
Guido Governatori and Antonino Rotolo.
Defeasible logic: Agency and obligation. In Alessio Lomuscio and Donald Nute, editors, Deontic Logic in Computer Science, number 3065 in LNAI, pages 114-128, Springer-Verlag, Berlin, 2004. Copyright © 2004 Springer.
Abstract:We propose a computationally oriented non-monotonic multi-modal logic arising from the combination of agency, intention and obligation. We argue about the defeasible nature of these notions and then we show how to represent and reason with them in the setting of defeasible logic.
 
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: 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.
 
Guido Governatori and Antonino Rotolo.
On the complexity of temporal defeasible logic. In Thomas Meyer and Eugenia Ternovska, editors, 13 International Workshop on Non-Monotonic Reasoning (NMR 2010), CEUR Workshop Proceedings, 2010.
Abstract: In this paper we investigate the complexity of temporal defeasible logic, and we propose an efficient algorithm to compute the extension of a temporalised defeasible theory. We motivate the logic showing how it can be used to model deadlines.
 
Guido Governatori, Antonino Rotolo, Régis Riveret, Monica Palmirani and Giovanni Sartor.
Variations of Temporal Defeasible Logic for Modelling Norm Modifications. In Radboud Winkels, editor, Proceedings of 11th International Conference on Artificial Intelligence and Law, pp. 155-159. ACM Press, New York, 2007. Copyright © 2007 ACM
Abstract: This paper proposes some variants of Temporal Defeasible Logic (TDL) to reason about normative modifications. These variants make it possible to differentiate cases in which, for example, modifications at some time change legal rules but their conclusions persist afterwards from cases where also their conclusions are blocked.
 
Guido Governatori, Antonino Rotolo, and Giovanni Sartor.
Temporalised normative positions in defeasible logic. In Anne Gardner, editor, Procedings of the 10th International Conference on Artificial Intelligence and Law, pages 25-34. ACM Press, 6-10 June 2005, Copyright © 2005 ACM.
Abstract:We propose a computationally oriented non-monotonic multi-modal logic arising from the combination of temporalised agency and temporalised normative positions. We argue about the defeasible nature of these notions and then we show how to represent and reason with them in the setting of Defeasible Logic.
 
Guido Governatori and Giovanni Sartor.
Burdens of proof in monological argumentation. In Radboud Winkels, editor, Legal Knowledge and Information Systems JURIX 2010: The Twenty-Third Annual Conference, Frontiers in Artificial Intelligence and Applications, Amsterdam, 2010. IOS Press.
Abstract: We shall argue that burdens of proof are relevant also to monological reasoning, i.e., for deriving the conclusions of a knowledge-base allowing for conflicting arguments. Reasoning with burdens of proof can provide a useful extension of current argument-based non-monotonic logics, at least a different perspective on them. Firstly we shall provide an objective characterisation of burdens of proof, assuming that burdens concerns rule antecedents (literals in the body of rules), rather than agents. Secondly, we shall analyse the conditions for a burden to be satisfied, by considering credulous or skeptical derivability of the concerned antecedent or of its complement. Finally, we shall develop a method for developing inferences out of a knowledge base merging rules and proof burdens in the framework of defeasible logic.
 
Ho-Pun Lam and Guido Governatori.
On the problem of computing ambiguity propagation and well-founded semantics in defeasible logic. In Mike Dean, John Hall, Antonino Rotolo, and Said Tabet, editors, RuleML 2010: 4th International Web Rule Symposium, number 6403 in LNCS, pages 119-127, Berlin, 2010. Springer, ">Copyrigth © 2010 Springer.
Abstract: In this paper we present the well founded variants of ambiguityblocking and ambiguity propagating defeasible logics. We also show how to extend SPINdle, a state of the art, defeasible logic implementation to handle all such variants of defeasible logic.
 
Ho-Pun Lam and Guido Governatori.
What are the necessity rules in defeasible reasoning?. In James Delgrande and Wolfgang Faber, editors, 11th International Conference on Logic Programming and Nonmonotonic Reasoning (LPNMAR 2011), Lecture Notes in Computer Science. Springer, 2011. Copyrigth © 2011 Springer.
Abstract: This paper investigates a new approach for computing the inference of defeasible logic. The algorithm proposed can substantially reduced the theory size increase due to transformations while preserving the representation properties in different variants of DL. Experiments also show that our algorithm outperform traditional approach by several order of amplitudes.
 
Michael J. Maher and Guido Governatori.
A semantic decomposition of defeasible logic. In Proc. American National Conference on Artificial Intelligence (AAAI-99), pages 299-305, Menlo Park, CA, 1999. AAAI Press, Copyright © 1999 AAAI, American Association for Artificial Intelligence.
Abstract:We investigate defeasible logics using a technique which decomposes the semantics of such logics into two parts: a specification of the structure of defeasible reasoning and a semantics for the meta-language in which the specification is written. We show that Nute's Defeasible Logic corresponds to Kunen's semantics, and develop a defeasible logic from the well-founded semantics of Van Gelder, Ross and Schlipf. We also obtain a new defeasible logic which extends an existing language by modifying the specification of Defeasible Logic. Thus our approach is productive in analysing, comparing and designing defeasible logics.
 
Duy Hoang Pham, Subhasis Thakur, and Guido Governatori.
Settling on the group's goals: An n-person argumentation game approach. In The Duy Bui, Tuong Vinh Ho, and Quang-Thuy Ha, editors, 11th Pacific Rim International Conference on Multi-Agents (PRIMA 2008), Lecture Notes in Computer Science 5357, pages 328-339. Springer, 2008, Copyright © 2008 Springer.
Abstract: Argumentation games have been proved to be a robust and flexible tool to resolve conflicts among agents. An agent can propose its explanation and its goal known as a claim, which can be refuted by other agents. The situation is more complicated when there are more than two agents playing the game. We propose a weighting mechanism for competing premises to tackle with conflicts from multiple agents in an n-person game. An agent can defend its proposal by giving a counter-argument to change the ``opinion'' of the majority of opposing agents. During the game, an agent can exploit the knowledge that other agents expose in order to promote and defend its main claim.
 
Duy Hoang Pham, Subhasis Thakur, and Guido Governatori.
Defeasible logic to model n-person argumentation game. In Maurice Pagnuco and Michael Thielscher, editors, Twelfth International Workshop on Non-Monotonic Reasoning, pages 215-222, 13--15 September 2008.
Abstract: In multi-agent systems, an individual agent can pursue its own goals, which may conflict with those hold by other agents. To settle on a common goal for the group of agents, the argumentation/dialogue game provides a robust and flexible tool where an agent can send its explanation for its goal in order to convince other agents. In the setting that the number of agents is greater than two and they are equally trustful, it is not clear how to extend existing argumentation/dialogue frameworks to tackle conflicts from many agents. We propose to use the defeasible logic to model the n-person argumentation game and to use the majority rule as an additional preference mechanism to tackle conflicts between arguments from individual agents.
 
Duy Hoang Pham, Guido Governatori, and Subhasis Thakur.
Extended defeasible reasoning for common goals in n-person argumentation games. Journal of Universal Computer Science, 15 no. 13 pp. 2653--2675, 2009.
Abstract: Argumentation games have been proved to be a robust and flexible tool to resolve conflicts among agents. An agent can propose its explanation and its goal known as a claim, which can be refuted by other agents. The situation is more complicated when there are more than two agents playing the game. We propose a weighting mechanism for competing premises to tackle with conflicts from multiple agents in an n-person game. An agent can defend its proposal by giving a counter-argument to change the "opinion" of the majority of opposing agents. Furthermore, using the extended defeasible reasoning an agent can exploit the knowledge that other agents expose in order to promote and defend its main claim.
 
Pakornpong Pothipruk and Guido Governatori.
ALE Defeasible Description Logic. In Abdul Sattar and Byeong Ho Kang, editor, 19th Australian Joint Conference on Artificial Intelligence, Hobart. pages 110-119. Lecture Notes in Computer Science 4304. Springer, Berlin, 2006. The original publication is available at www.springerlink.com
Abstract: One of Semantic Web strengths is the ability to address incomplete knowledge. However, at present, it cannot handle incomplete knowledge directly. Also, it cannot handle non-monotonic reasoning. In this paper, we extend ALC-. Defeasible Description Logic with existential quantifier, i.e., ALE Defeasible Description Logic. Also, we modify some parts of the logic, resulting in an increasing efficiency in its reasoning.
 
Bram Roth, Régis Riveret, Antonino Rotolo and Guido Governatori.
Strategic Argumentation: A Game Theoretical Investigation. In Radboud Winkels, editor, Proceedings of 11th International Conference on Artificial Intelligence and Law, pp. 81-90. ACM Press, New York, 2007. Copyright © 2007 ACM
Abstract: Argumentation is modelled as a game where the payoffs are measured in terms of the probability that the claimed conclusion is, or is not, defeasibly provable, given a history of arguments that have actually been exchanged, and given the probability of the factual premises. The probability of a conclusion is calculated using a standard variant of Defeasible Logic, in combination with standard probability calculus. It is a new element of the present approach that the exchange of arguments is analysed with game theoretical tools, yielding a prescriptive and to some extent even predictive account of the actual course of play. A brief comparison with existing argument-based dialogue approaches confirms that such a prescriptive account of the actual argumentation has been almost lacking in the approaches proposed so far.
 
Insu Song and Guido Governatori.
Hardware Implementation of Temporal Nonmonotonic Logics. In Abdul Sattar and Byeong Ho Kang, editor, 19th Australian Joint Conference on Artificial Intelligence, Hobart, 4-8 December. pages 808-817. Lecture Notes in Computer Science 4304. Springer, Berlin, 2006. The original publication is available at www.springerlink.com
Abstract: In order to apply nonmonotonic logics for specifying industrial automation controllers, we define (1) a method to extend atemporal nonmonotonic logics with temporal operators and (2) a mapping of these new temporal nonmonotonic logics into a Metric Temporal Logic. This mapping provides a formal specification method for real-time temporal reasoning digital circuits for the temporal nonmonotonic logics. We present our method in the context of synthesizing custom digital hardware (called agent chip) automatically from high level agent specifications.
 
Insu Song, Guido Governatori, and Joachim Diederich.
Automatic synthesis of reactive agents. In 11th International Conference on Control, Automation, Robotics and Vision, ICARCV 2010. IEEE Press, December 7-10 2010. Copyrigth © 2010 IEEE.
Abstract: This paper introduces a new approach to designing smart control chips that enables automatic synthesis of real-time control systems from agent specifications. An agent specification is compiled into a hardware description format, such as RTL-VHDL (Register Transfer Level--VLSI Hardware Description Language) or RTL Verilog, which is synthesized using computer-assisted tools to develop ASIC masks or FPGA configurations. A rule-based specification language called Layered Argumentation System (LAS) is defined and a sound and complete mapping to Verilog is developed. LAS combines fuzzy reasoning and non-monotonic reasoning. This enables chip designers to capture commonsense knowledge and concepts having varying degrees of confidence collaboratively and incrementally.
 
Insu Song, Guido Governatori, and Joachim Diederich.
Layered argumentation for fuzzy automation controllers. In IEEE Conference on Cybernetics and Intelligent Systems (CIS), , pages 189-194. IEEE Press, June 28-30 2010, Copyrigth © 2010 IEEE.
Abstract: We develop a layered argumentation system (LAS) for efficient implementation of Fuzzy automation controllers. LAS extends a logic based proposal of argumentation with subsumption concept and varying degree of confidences in beliefs. We show that this argumentation system can be used to model Fuzzy automation controllers. The argumentation system is based on a nonmonotonic logic, the computational complexity of which is known to be linear to the size of the knowledge base. LAS theories can also be mapped into RTL-VHDL (Register Transfer Level-VLSI Hardware Description Language) or RTL Verilog for very efficient hardware implementation of Fuzzy automation controllers.
 
Subhasis Thakur, Guido Governatori, Vineet Padmanabhan, and Jenny Eriksson Lundström.
Dialogue games in defeasible logic. In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint Conference on Artificial Intelligence, AI 2007, LNAI 4830, pages 497-506. Springer, 2007. Copyright © 2007 Springer.
Abstract: In this paper we show how to capture dialogue games in Defeasible Logic. We argue that Defeasible Logic is a natural candidate and general representation formalism to capture dialogue games even with requirements more complex than existing formalisms for this kind of games. We parse the dialogue into defeasible rules with time of the dialogue as time of the rule. As the dialogue evolves we allow an agent to upgrade the strength of unchallenged rules. The proof procedures of (Antoniou, Billington, Governatori, Maher 2001) are used to determine the winner of a dialogue game.