Publications on Defeasible Logic

Grigoris Antoniou, David Billington, Guido Governatori, and Michael J. Maher.
On the modeling and analysis of regulations. In Proceedings of the Australian Conference Information Systems, pages 20-29, 1999.
Abstract:Regulations are a wide-spread and important part of government and business. They codify how products must be made and processes should be performed. Such regulations can be difficult to understand and apply. In an environment of growing complexity of, and change in, regulation, automated support for reasoning with regulations is becoming increasingly necessary. In this paper we report on ongoing work which aims at providing automated support for the drafting and use of regulations using logic modelling techniques. We highlight the support that can be provided by logic modelling, describe the technical foundation of our project, and report on the status of the project and the next steps.
 
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, Copyrigth © 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., Copyrigth © 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, Nikos Dimaresis, and Guido Governatori.
A system for modal and deontic defeasible reasoning. In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint Conference on Artificial Intelligence, AI 2007, LNAI 4830, pages 609-613. Springer, 2007. Copyrigth © 2007 Springer.
Abstract: Defeasible reasoning is a well-established nonmonotonic reasoning approach that has recently been combined with semantic web technologies. This paper describes modal and deontic extensions of defeasible logic, motivated by potential applications for modelling multi-agent systems and policies. It describes a logic metaprogram that captures the underlying intuitions, and outlines an implemented system.
 
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, Copyrigth © 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.
 
Nick Bassiliades, Grigoris Antoniou and Guido Governatori.
Proof Explanation in the DR-DEVICE System. In M. Marchiori, J.Z.Pan and C. de Sainte Marie (eds) Web Reasoning and Rule Systems, LNCS 4524, pages 249-258. Springer, Berlin, 2007. Copyright © 2007 Springer.
Abstract: Trust is a vital feature for the Semantic Web: If users (humans and agents) are to use and integrate system answers, they must trust them. Thus, systems should be able to explain their actions, sources, and beliefs, and this issue is the topic of the proof layer in the design of the Semantic Web. This paper presents the design of a system for proof explanation on the Semantic Web, based on defeasible reasoning. The basis of this work is the DR-DEVICE system that is extended to handle proofs. A critical aspect is the representation of proofs in an XML language, which is achieved by a RuleML language extension.
 
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, Copyrigth © 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, Joris Hulstijn, Régis Riveret, Antonino Rotolo, and Leendert van der Torre.
Time and defeasibility in FIPA ACL semantics. In 2008 IEEE/WIC/ACM International Conference on Web Intelligence and Intelligent Agent Technology, pages 634-637. IEEE Press, 2008, Copyrigth © 2008 IEEE.
Abstract: Inferences about communicative actions are often conditional, non-monotonic, and involve the issue of time. Most agent communication languages, however, ignore these issues, due to the difficulty to combine them in a single formalism. This paper addresses such issues in defeasible logic, and illustrates how to express a semantics for ACLs in order to make non-monotonic inferences on the basis of communicative actions.
 
Guido Boella, Guido Governatori, Joris Hulstijn, Régis Riveret, Antonino Rotolo and Leemndert van der Torre.
FIPA Communicative Acts in Defeasible Logic. In Alankar Karol, Pavlos Peppas and Mary-Anne Williams, editor, Seventh IJCAI International Workshop on Nonmonotonic Reasoning, Action and Change (NRAC'07), Hyderabad, India, 7-8 January, 2007.
Abstract: In agent communication languages, the inferences that can be made on the basis of a communicative action are inherently conditional, and non-monotonic. For example, a proposal only leads to a commitment, on the condition that it is accepted. And in a persuasion dialogue, assertions may later be retracted. In this paper we therefore present a defeasible logic that can be used to express a semantics for agent communication languages, and to efficiently make inferences on the basis of communicative actions. The logic is non-monotonic, allows nested rules and mental attitudes as the content of communicative actions, and has an explicit way of expressing persistence over time. Moreover, it expresses that mental attitudes are publicly attributed to agents playing roles in the dialogue. To illustrate the usefulness of the logic, we reformalize the meta-theory underlying the FIPA semantics for agent communication, focusing on inform and propose. We show how composed speech acts can be formalized, and extend the semantics with an account of persuasion.
 
Mehdi Dastani, Guido Governatori, Antonio Rotolo, Insu Song and Leendert van der Torre.
Contextual Deliberation of Cognitive Agents in Defeasible Logic. In 6th International Conference on Autonomous Agents and Multi-Agent Systems. ACM Press, New York. Copyright © 2007 ACM.
Abstract: This article extends Defeasible Logic to deal with the contextual deliberation process of cognitive agents. First, we introduce meta-rules to reason with rules. Meta-rules are rules that have as a consequent rules for motivational components, such as obligations, intentions and desires. In other words, they include nested rules. Second, we introduce explicit preferences among rules. They deal with complex structures where nested rules can be involved.
 
Mehdi Dastani, Guido Governatori, Antonino Rotolo, Insu Song, and Leendert van der Torre.
Contextual agent deliberation in defeasible logic. In Aditya Ghose and Guido Governatori, editors, 10 Pacific Rim International Workshop on Multi-Agents, LNAI 5044. Springer, 2008 Copyrigth © 2008 Springer.
Abstract: This article extends Defeasible Logic to deal with the contextual deliberation process of cognitive agents. First, we introduce meta-rules to reason with rules. Meta-rules are rules that have as a consequent rules for motivational components, such as obligations, intentions and desires. In other words, they include nested rules. Second, we introduce explicit preferences among rules. They deal with complex structures where nested rules can be involved.
 
Mehdi Dastani, Guido Governatori, Antonino Rotolo and Leendert van der Torre
Preferences of Agents in Defeasible Logic. In S. Zhang and R. Jarvis, editors, Australian Joint Conference on Artificial Intelligence, AI 2005, pages 695-704. LNCS 3809, Springer, Berlin, 2005, Copyrigth © 2005 Springer.
Abstract: We are interested in programming languages for cognitive agents with preferences. We define rule-based agent theories and inference procedures in defeasible logic, and in this setting we discuss patterns of agent behavior called agent types.
 
Mehdi Dastani, Guido Governatori, Antonino Rotolo and Leendert van der Torr
Programming Cognitive Agents in Defeasible Logic. In G. Sutcliffe and A. Voronkov, editors, Logic Programming and Automated Reasoning. LPAR 2005, pages 621-635. LNCS 3835, Springer, Berlin, 2005, Copyrigth © 2005 Springer.
Abstract: Defeasible Logic is extended to programming languages for cognitive agents with preferences and actions for planning. We define rule-based agent theories that contain preferences and actions, together with inference procedures. We discuss patterns of agent types in this setting. Finally, we illustrate the language by an example of an agent reasoning about web-services.
 
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 Copyrigth © 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.
Representing business contracts in RuleML. International Journal of Cooperative Information Systems, 14 no. 2-3, June-September 2005, pp. 181-216.
Abstract:This paper presents an approach for the specification and implementation of translating contracts from a human-oriented form into an executable representation for monitoring. This will be done in the setting of RuleML. The task of monitoring contract execution and performance requires a logical account of deontic and defeasible aspects of legal language; currently such aspects are not covered by RuleML; accordingly we show how to extend it to cover such notions. From its logical form, the contract will be thus transformed into a machine readable rule notation and eventually implemented as executable semantics via any mark-up languages depending on the client's preference, for contract monitoring purposes.
 
Guido Governatori, Marlon Dumas, Arthur H.M. ter Hofstede, and Phillipa Oaks.
A formal approach to protocols and strategies for (legal) negotiation. In Henry Prakken, editor, Procedings of the 8th International Conference on Artificial Intelligence and Law, pages 168-177. IAAIL, ACM Press, 2001, Copyrigth © 2001 ACM.
Abstract:We propose a formal and executable framework for expressing protocols and strategies for automated (legal) negotiation. In this framework a party involved in a negotiation is represented through a software agent composed of four modules: (i) a communication module which manages the interaction with the other agents; (ii) a control module; (iii) a reasoning module specified as a defeasible theory; and (iv) a knowledge base which bridges the control and the reasoning modules, while keeping track of past decisions and interactions. The choice of defeasible logic is justified against a set of desirable criteria for negotiation automation languages. Moreover, the suitability of the framework is illustrated through two case studies.
 
Guido Governatori, Joris Hulstijn, Régis Riveret, and Antonino Rotolo.
Characterising deadlines in temporal modal defeasible logic. In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint Conference on Artificial Intelligence, AI 2007, LNAI 4830, pages 486-496. Springer, 2007. Copyrigth © 2007 Springer.
Abstract: We provide a conceptual analysis of several kinds of deadlines, represented in Temporal Modal Defeasible Logic. The paper presents a typology of deadlines, based on the following parameters: deontic operator, maintenance or achievement, presence or absence of sanctions, and persistence after the deadline. The deadline types are illustrated by a set of examples.
 
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, Copyrigth © 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. Copyrigth © 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 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. Copyrigth © 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, Vineet Padmanabhan, and Antonino Rotolo.
Rule-based agents in temporalised defeasible logic. In Qiang Yang and Geoff Webb, editors, Ninth Pacific Rim International Conference on Artificial Intelligence, LNAI 4099, pages 31-40, Guilin, 7-11 August 2006. Springer, Copyrigth © 2006 Springer.
Abstract:This paper provides a framework based on temporal defeasible logic to reason about deliberative rule-based cognitive agents. Compared to previous works in this area our framework has the advantage that it can reason about temporal rules. We show that for rule-based cognitive agents deliberation is more than just deriving conclusions in terms of their mental components. Our paper is an extension of [5,6] in the area of cognitive agent programming.
 
Guido Governatori, Vineet Padmanabhan, Antonino Rotolo, and Abdul Sattar.
A defeasible logic for modelling policy-based intentions and motivational attitudes. Logic Journal of the IGPL, 17(3), 2009. Copyrigth © 2009 Oxford University Press.
Abstract: In this paper we show how defeasible logic could formally account for the non-monotonic properties involved in motivational attitudes like intention and obligation. Usually, normal modal operators are used to represent such attitudes wherein classical logical consequence and the rule of necessitation comes into play i.e., $\vdash A / \vdash \Box A$, that is from $\vdash A$ derive $\vdash\Box A$. This means that such formalisms are affected by the Logical Omniscience problem. We show 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 that specifies how modalities can be introduced and manipulated in a non-monotonic setting without giving rise to the problem of logical omniscience. In a similar way we show how to add deontic modalities defeasibly and how to integrate them with other motivational attitudes like beliefs and goals. Finally we show that the basic aspect of the BOID architecture is captured by this extended framework.
 
Guido Governatori, Monica Palmirani, Régis Riveret, Antonino Rotolo and Giovanni Sartor.
Norm Modifications in Defeasible Logic. In Marie-Francine Moens, editor, Jurix'05: The Eighteenth Annual Conference, pages 13-22. IOS Press, Amsterdam 2005.
Abstract: This paper proposes a framework based on Defeasible Logic (DL) to reason about normative modifications. We show how to express them in DL and how the logic deals with conflicts between temporalised normative modifications. Some comments will be given with regard to the phenomenon of retroactivity.
 
Guido Governatori, and Duy Hoang Pham
DR-CONTRACT: An Architecture for e-Contracts in Defeasible Logic In Claudio Bartolini, Guido Governatori, and Zoran Milosevic (eds). Proceedings on the 2nd EDOC Workshop on Contract Architecures and Languages (CoALa 2005). Enschede, NL, 20 September 2005. IEEE Press.
Abstract:In this paper we present an architecture to represent and reason on e-Contracts based on the DR-device architecture supplemented with a deontic defeasible logic of violation. We motivate the choice for the logic and we show how to extend RuleML to capture the notions relevant to describe e-contracts for a monitoring perspective in Defeasible Logic.
 
Guido Governatori and Duy Hoang Pham
A Semantic Web Based Architecture for e-Contracts in Defeasible Logic. In A. Adi, S. Stoutenberg and S. Tabet, editors, Rules and Rule Markup Languages for the Semantic Web. RuleML 2005, pages 145-159. LNCS 3791, Springer, Berlin, 2005. The original pubblication is available at www.springerlink.com.
Abstract: We introduce the DR-CONTRACT architecture to represent and reason on e-Contracts. The architecture extends the DR-device architecture by a deontic defeasible logic of violation. We motivate the choice for the logic and we show how to extend RuleML to capture the notions relevant to describe e-contracts for a monitoring perspective in Defeasible Logic.
 
Guido Governatori and Duy Hoang Pham.
DR-CONTRACT: An Architecture for e-Contracts in Defeasible Logic. International Journal of Business Process Integration and Management, 5(4), 2009.
Abstract: We introduce the DR-CONTRACT architecture to represent and reason on e-Contracts. The architecture extends the DR-device architecture by a deontic defeasible logic of violation. We motivate the choice for the logic and we show how to extend RuleML to capture the notions relevant to describe e-contracts for a monitoring perspective in Defeasible Logic.
 
Guido Governatori, Duy Hoang Pham, Simon Raboczi, Andrew Newman, and Subhasis Thakur.
On extending RuleML for modal defeasible logic. In Nick Bassiliades, Guido Governatori, and Adrian Paschke, editors, RuleML 2008: The International RuleML Symposium on Rule Interchange and Applications, Lecture Notes in Computer Science, Berlin, 2008. Springer, Copyrigth © 2008 Springer.
Abstract: In this paper we present a general methodology to extend Defeasible Logic with modal operators. We motivate the reasons for this type of extension and we argue that the extension will allow for a robust knowledge framework in different application areas. The paper presents an extension of RuleML to capture Modal Defeasible Logic.
 
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.
Representing contracts using RuleML. In Thomas Gordon, editor, Legal Knowledge and Information Systems, volume 120 of Frontieres in Artificial Intelligence and Applications, pages 141-150, Amsterdam, 2004. IOS Press.
Abstract:This paper presents an approach for the specification and implementation of e-contracts for Web monitoring. This is done in the setting of RuleML. We argue that monitoring contract execution requires also a logical account of deontic concepts and of violations. Accordingly, RuleML is extended to cover these aspects.
 
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. Copyrigth © 2004 Spinger.
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.
BIO logical agents: Norms, beliefs, intentions in defeasible logic. Journal of Autonomous Agents and Multi Agent Systems, 2008. Copyrigth © 2008 Springer.
Abstract: In this paper we follow the BOID (Belief, Obligation, Intention, Desire) architecture to describe agents and agent types in Defeasible Logic. We argue, in particular, that the introduction of obligations can provide a new reading of the concepts of intention and intentionality. Then we examine the notion of social agent (i.e., an agent where obligations prevail over intentions) and discuss some computational and philosophical issues related to it. We show that the notion of social agent either requires more complex computations or has some philosophical drawbacks.
 
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. Copyrigth © 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.
An algorithm for business process compliance. In Enrico Francesconi, Giovani Sartor, and Daniela Tiscornia, editors, Legal Knowledge and Information Systems (Jurix 2008), Frontieres in Artificial Intelligence and Applications 189, pages 186-191. IOS Press, 2008.
Abstract: This paper provides a novel mechanism to check whether business processes are compliant with business rules regulating them. The key point is that compliance is a relationship between two sets of specifications: the specifications for executing a business process and the specifications regulating it.
 
Guido Governatori and Antonino Rotolo.
A computational framework for institutional agency. Artificial Intelligence and Law, 16 no. 1 pp. 25-52, 2008, Copyrigth © 2008 Springer.
Abstract: This paper provides a computational framework, based on Defeasible Logic, to capture some aspects of institutional agency. Our background is Kanger-Lindahl-Pörn account of organised interaction, which describes this interaction within a multi-modal logical setting. This work focuses in particular on the notions of counts-as link and on those of attempt and of personal and direct action to realise states of affairs. We show how standard Defeasible Logic can be extended to represent these concepts: the resulting system preserves some basic properties commonly attributed to them. In addition, the framework enjoys nice computational properties, as it turns out that the extension of any theory can be computed in time linear to the size of the theory itself.
 
Guido Governatori, Antonino Rotolo and Vineet Padmanabhan.
The Cost of Social Agents. In 5th International Conference on Autonomous Agents and Multi-Agent Systems (AAMAS06), pages 513-520. ACM Press, 2006. Copyright © 2006 ACM.
Abstract: In this paper we follow the BOID (Belief, Obligation, Intention, Desire) architecture to describe agents and agent types in Defeasible Logic. We argue that the introduction of obligations can provide a new reading of the concepts of intention and intentionality. Then we examine the notion of social agent (i.e., an agent where obligations prevail over intentions) and discuss some computational and philosophical issues related to it. We show that the notion of social agent either requires more complex computations or has some philosophical drawbacks.
 
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 Shazia Sadiq.
A model of dynamic resource allocation in workflow systems. In Klaus-Dieter Schewe and Hugh E. Williams, editors, Database Technology 2004, number 27 in Conference Research and Practice of Information Technology, pages 197-206. Australian Computer Science Association, ACS, 2004. Copyrigth © 2004 ACS.
Abstract:Current collaborative work environments are characterized by dynamically changing organizational structures. Although there have been several efforts to refine work distribution, especially in workflow management, most literature assumes a static database approach which captures organizational roles, groups and hierarchies and implements a dynamic roles based agent assignment protocol. However, in practice only partial information may be available for organizational models, and in turn a large number of exceptions may emerge at the time of work assignment. In this paper we present an organizational model based on a policy based normative system. The model is based on a combination of an intensional logic of agency and a flexible, but computationally feasible, non-monotonic formalism (Defeasible Logic). Although this paper focuses on the model specification, the proposed approach to modelling agent societies provides a means of reasoning with partial and unpredictable information as is typical of organizational agents in workflow systems.
 
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, 2005, Copyrigth © 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 Shazia Sadiq.
The journey to business process compliance. In Jorge Cardoso and Wil van der Aalst, editors, Handbook of Research on BPM, IGI Global, 2009.
Abstract: It is a typical scenario that many organisations have their business processes specified independently of their business obligations (which includes contractual obligations to business partners, as well as obligations a business has to fulfil against regulations and industry standards). This is because of the lack of guidelines and tools that facilitate derivation of processes from contracts but also because of the traditional mindset of treating contracts separately from business processes. This chapter will provide a solution to one specific problem that arises from this situation, namely the lack of mechanisms to check whether business processes are compliant with business contracts. The chapter begins by defining the space for business process compliance and the eco-system for ensuring that process are compliant. The key point is that compliance is a relationship between two sets of specifications: the specifications for executing a business process and the specifications regulating a business. The central part of the chapter focuses on a logic based formalism for describing both the semantics of normative specifications and the semantics of compliance checking procedures.
 
Guido Governatori and Paolo Terenziani.
Temporal extensions to defeasible logic. In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint Conference on Artificial Intelligence, AI 2007, Gold Coast, 2-6 December 2007. Copyrigth © 2007 Springer. The original publication is available at www.springerlink.com.
Abstract: In this paper, we extend Defeasible Logic (a computationally-oriented non-monotonic logic) in order to deal with temporalised rules. In particular, we extend the logic to cope with durative facts, as well as with delays between the antecedent and the consequent of rules. We showed that the extended temporalised framework is suitable to model different types of causal relations which have been identified by the specialised literature. We also prove that the computational properties of the original logic are still retained by the extended approach.
 
Guido Governatori, Subhasis Thakur, and Duy Hoang Pham.
A compliance model of trust. In Enrico Francesconi, Giovani Sartor, and Daniela Tiscornia, editors, Legal Knowledge and Information Systems (Jurix 2008), Frontieres in Artificial Intelligence and Applications 189, pages 118-127. IOS Press, 2008.
Abstract: We present a model of past interaction trust model based on compliance of expected behaviours.
 
Efsrations Kontopoulos, Nick Bassiliades, Guido Governatori, and Grigoris Antoniou.
Extending a defeasible reasoner with modal and deontic logic operators. In 2008 IEEE/WIC/ACM International Conference on Web Intelligence and Intelligent Agent Technology, pages 626-629. IEEE Press, 2008, Copyrigth © 2008 IEEE.
Abstract: Defeasible logic is a non-monotonic formalism that deals with incomplete and conflicting information. Modal logic deals with necessity and possibility, exhibiting defeasibility; thus, it is possible to combine defeasible logic with modal operators. This paper reports on the extension of the DR-DEVICE defeasible reasoner with modal and deontic logic operators. The aim is a practical defeasible reasoner that will take advantage of the expressiveness of modal logics and the flexibility to define diverse agent types and behaviors.
 
Guido Governatori and Andrew Stranieri.
Towards the application of association rules for defeasible rules discovery. In Bart Verheij, Arno Lodder, Ronald P. Loui, and Antoniette J. Muntjerwerff, editors, Legal Knowledge and Information Systems, pages 63-75, Amsterdam, 2001. JURIX, IOS Press.
Abstract:In this paper we investigate the feasibility of Knowledge Discovery from Database (KDD) in order to facilitate the discovery of defeasible rules that represent the ratio decidendi underpinning legal decision making. Moreover we will argue in favour of Defeasible Logic as the appropriate formal system in which the extracted principles should be encoded.
 
Guido Governatori and Paolo Terenziani.
Temporal extensions to defeasible logic. In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint Conference on Artificial Intelligence, AI 2007, LNAI 4830, pages 476-485. Springer, 2007. Copyrigth © 2007 Springer.
Abstract: In this paper, we extend Defeasible Logic (a computationally-oriented non-monotonic logic) in order to deal with temporalised rules. In particular, we extend the logic to cope with durative facts, as well as with delays between the antecedent and the consequent of rules. We showed that the extended temporalised framework is suitable to model different types of causal relations which have been identified by the specialised literature. We also prove that the computational properties of the original logic are still retained by the extended approach.
 
Guido Governatori, Arthur H.M. ter Hofstede, and Phillipa Oaks.
Defeasible logic for automated negotiation. In P. Swatman and P.M. Swatman, editors, Proceedings of CollECTeR. Deakin University, 2000. Published on CD.
Abstract:Negotiation plays a fundamental role in e-commerce. In this paper, the application of defeasible logic for automated negotiation is investigated. Defeasible logic is flexible enough to be adapted to several possible negotiation strategies, has efficient implementations, and provides a formal basis for analysis (e.g. to explain why a negotiation was not successful). Two case studies, one small and one more comprehensive, will be described and the feasibility of approaches based on defeasible logic will be discussed.
 
Guido Governatori, Arthur H.M. ter Hofstede, and Phillipa Oaks.
Is defeasible logic applicable?. In Grigoris Antoniou and Guido Governatori, editors, Proceedings of the 2nd Australasian Workshop on Computational Logic, pages 47-62, Brisbane, January 2001. Queensland University of Technology.
Abstract:In this paper the application of defeasible logic for automated negotiation is investigated. Defeasible logic is flexible enough to be adapted to several possible negotiation strategies, has efficient implementations, and provides a formal basis for analysis (e.g. to explain why a negotiation was not successful). Two case studies, one small and one more comprehensive, will be described and the feasibility of approaches based on defeasible logic will be discussed.
 
Benjamin Johnston and Guido Governatori.
Induction of defeasible logic theories in the legal domain. In Giovanni Sartor, editor, Procedings of the 9th International Conference on Artificial Intelligence and Law, pages 204-213. IAAIL, ACM Press, 2003. Copyrigth © 2003 ACM.
Abstract:The market for intelligent legal information systems remains relatively untapped and while this might be interpreted as an indication that it is simply impossible to produce a system that satisfies the needs of the legal community, an analysis of previous attempts at producing such systems reveals a common set of deficiencies that in-part explain why there have been no overwhelming successes to date. Defeasible logic, a logic with proven successes at representing legal knowledge, seems to overcome many of these deficiencies and is a promising approach to representing legal knowledge. Unfortunately, an immediate application of technology to the challenges in this domain is an expensive and computationally intractable problem. So, in light of the benefits, we seek to find a practical algorithm that uses heuristics to discover an approximate solution. As an outcome of this work, we have developed an algorithm that integrates defeasible logic into a decision support system by automatically deriving its knowledge from databases of precedents. Experiments with the new algorithm are very promising - delivering results comparable to and exceeding other approaches.
 
Benjamin Johnston and Guido Goverantori.
An algorithm for the induction of defeasible logic theories from databases. In Klaus-Dieter Schewe and Xiaofang Zhou, editors, Database Technology 2003, number 17 in Conference Research and Practice of Information Technology, pages 75-83. Australian Computer Science Association, ACS, 4-7 February 2003. Copyrigth © 2003 ACS.
Abstract:Defeasible logic is a non-monotonic logic with applications in rule-based domains such as law. To ease the development and improve the accuracy of expert systems based on defeasible logic, it is desirable to automatically induce a theory of the logic from a training set of precedent data. Empirical evidence suggests that minimal theories that describe the training set tend to be more faithful representations of reality. We show via transformation from the hitting set problem that this global minimization problem is intractable, belonging to the class of NP optimisation problems. Given the inherent difficulty of finding the optimal solution, we instead use heuristics and demonstrate that a best-first, greedy, branch and bound algorithm can be used to find good theories in short time. This approach displays significant improvements in both accuracy and theory size as compared to recent work in the area that post-processed the output of an Aprori association rule-mining algorithm, with comparable execution times.
 
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, Copyrigth © 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, Guido Governatori, and Simon Raboczi.
Agents adapt to majority behaviours. In The 2008 IEEE International Conference on Research, Innovation and Vision for the Future, 2008. RIVF'08, IEEE, 2008, Copyrigth © 2008 IEEE.
Abstract: Agents within a group can have different perceptions of their working environment and autonomously fulfil their goals. However, they can be aware of beliefs and goals of the group as well as other members so that they can adjust their behaviours accordingly. To model these agents, we explicitly include knowledge commonly shared by the group and that obtained from other agents. By avoiding actions which violate ``mental attitudes'' shared by the majority of the group, agents demonstrate their social commitment to the group. Defeasible logic is chosen as our representation formalism for its computational efficiency, and for its ability to handle incomplete and conflicting information. Hence, our agents can enjoy the low computational cost while performing ``reasoning about others''. Finally, we present the implementation of our multi-agent system.
 
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.
 
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.
 
Régis Riveret, Guido Governatori, and Antonino Rotolo.
Argumentation semantics for temporal defeasible logic. In Pavlos Peppas, Anna Perini, and Loris Penserini, editors, Third European Starting AI Researcher Symposium (STAIRS 2006), pages 267-268, Riva del Garda, 28-29 August 2006. IOS Press, Amsterdam, 2006.
Abstract: We present an extension of the argumentation semantics for defeasible logic to cover the temporalisation of defeasible logic with permanent and immanent temporal literals.
 
Régis Riveret, Antonino Rotolo and Guido Governatori.
Interaction between Normative Systems and Cognitive agents in Temporal Modal Defeasible Logic. In Guido Boella, Leon van der Torre and Harko Verhagen, editors, Normative Multi-agent Systems. Dagstuhl Seminar Proceedings 7122. Internationales Begegnungs- und Forschungszentrum fuer Informatik (IBFI), Schloss Dagstuhl, Germany, Dagstuhl, Germany, 2007.
Abstract: While some recent frameworks on cognitive agents addressed the combination of mental attitudes with deontic concepts, they commonly ignore the representation of time. We propose in this paper a variant of Temporal Modal Defeasible Logic to deal in particular with temporal intervals.
 
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.
 
Thomas Skylogiannis, Grigoris Antoniou, Nick Bassiliades, and Guido Governatori.
DR-NEGOTIATE - a system for automated agent negotiation with defeasible logic-based strategies. In Proceedings of The 2005 IEEE International Conference on e-Technology, e-Commerce and e-Service, 2005. EEE'05, pages 44-49. IEEE Press, 29 March - 1 April 2005, Copyrigth © 2005 IEEE.
Abstract:This paper reports on a system for automated agent negotiation. It uses the JADE agent framework, and its major distinctive feature is the use of declarative negotiation strategies. The negotiation strategies are expressed in a declarative rules language, defeasible logic and are applied using the implemented defeasible reasoning system DR-DEVICE. The choice of defeasible logic is justified. The overall system architecture is described, and a particular negotiation case is presented in detail.
 
Thomas Skylogiannis, Grigoris Antoniou, Nick Bassiliades, Guido Governatori and Antonis Bikakis.
DR-NEGOTIATE — A System for Automated Agent Negotiation with Defeasible Logic-Based Strategies. Data & Knowledge Engineering: 2007. Copyright © 2007 Elsevier B.V.
Abstract: This paper reports on a system for automated agent negotiation, based on a formal and executable approach to capture the behavior of parties involved in a negotiation. It uses the JADE agent framework, and its major distinctive feature is the use of declarative negotiation strategies. The negotiation strategies are expressed in a declarative rules language, defeasible logic, and are applied using the implemented system DR-DEVICE. The key ideas and the overall system architecture are described, and a particular negotiation case is presented in detail.
 
Insu Song and Guido Governatori
Nested Rules in Defeasible Logic. In A. Adi, S. Stoutenberg and S. Tabet, editors, Rules and Rule Markup Languages for the Semantic Web. RuleML 2005, pages 204-208. LNCS 3791, Springer, Berlin, 2005. The original pubblication is available at www.springerlink.com.
Abstract: Defeasible Logic is a rule-based non-monotonic logic with tractable reasoning services. In this paper we extend Defeasible Logic with nested rules. We consider a new Defeasible Logic, called DL$^{ns}$, where we allow one level of nested rules. A nested rule is a rule where the antecedent or the consequent of the rule are rules themselves. The inference conditions for DL$^{ns}$ are based on reflection on the inference structures (rules) of the particular theory at hand. Accordingly DL$^{ns}$ can be considered an amalgamated reflective system with implicit reflection mechanism. Finally we outline some possible applications of the logic.
 
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. Copyrigth © 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.