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See detailA Dynamic Approach for Combining Abstract Argumentation Semantics – Technical Report
Dauphin, Jérémie UL; Cramer, Marcos UL; van der Torre, Leon UL

Report (2018)

Abstract argumentation semantics provide a direct relation from an argumentation framework to corresponding sets of acceptable arguments, or equivalently to labeling functions. Instead, we study step-wise ... [more ▼]

Abstract argumentation semantics provide a direct relation from an argumentation framework to corresponding sets of acceptable arguments, or equivalently to labeling functions. Instead, we study step-wise update relations on argumentation frameworks whose fixpoints represent the labeling functions on the arguments. We make use of this dynamic approach in order to study novel ways of combining abstract argumentation semantics. In particular, we introduce the notion of a merge of two argumentation semantics, which is defined in such a way that the merge of the preferred and the grounded semantics is the complete semantics. Finally we consider how to define new semantics using the merge operator, in particular how meaningfully combine features of naive-based and complete-based semantics. [less ▲]

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See detailProceedings - 2017 ILILAS Distinguished Lectures
Bouvry, Pascal UL; Bisdorff, Raymond; Schommer, Christoph UL et al

Report (2018)

The Proceedings summarizes the 12 lectures that have taken place within the ILIAS Dinstguished Lecture series 2017. It contains a brief abstract of the talks as well as some additional information about ... [more ▼]

The Proceedings summarizes the 12 lectures that have taken place within the ILIAS Dinstguished Lecture series 2017. It contains a brief abstract of the talks as well as some additional information about each speaker. [less ▲]

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See detailRepresentation Equivalences among Argumentation Frameworks
Liao, Beishui; van der Torre, Leon UL

in Computational Models of Argument (2018)

In Dung’s abstract argumentation theory, an extension can be represented by subsets of it in the sense that from each of these subsets, the extension can be obtained again by iteratively applying the ... [more ▼]

In Dung’s abstract argumentation theory, an extension can be represented by subsets of it in the sense that from each of these subsets, the extension can be obtained again by iteratively applying the characteristic function. Such so-called regular representations can be used to differentiate argumentation frameworks having the same extensions. In this paper we provide a full characterization of relations between seven different types of representation equivalence. [less ▲]

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See detailAbstract and Concrete Decision Graphs for Choosing Extensions of Argumentation Frameworks - Technical Report
Dauphin, Jérémie UL; Cramer, Marcos UL; van der Torre, Leon UL

Report (2018)

Most argumentation semantics allow for multiple extensions, which raises the question of how to choose among extensions. We propose to study this question as a decision problem. Inspired by decision trees ... [more ▼]

Most argumentation semantics allow for multiple extensions, which raises the question of how to choose among extensions. We propose to study this question as a decision problem. Inspired by decision trees commonly used in economics, we introduce the notion of a decision graph for deciding between the multiple extensions of a given AF in a given semantics. We distinguish between abstract decision graphs and concrete instantiations thereof. Inspired by the principle-based approach to argumentation, we formulate two principles that mappings from argumentation frameworks to decision graphs should satisfy, the principle of decision-graph directionality and the one of directional decision-making. We then propose a concrete instantiation of decision graphs, which satisfies one of these principles. Finally, we discuss the potential for further research based on this novel methodology. [less ▲]

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See detailPreference in Abstract Argumentation
Kaci, Souhila; van der Torre, Leon UL; Villata, Serena

in Computational Models of Argument (2018)

Consider an argument A that is attacked by an argument B, while A is preferred to B. Existing approaches will either ignore the attack or reverse it. In this paper we introduce a new reduction of ... [more ▼]

Consider an argument A that is attacked by an argument B, while A is preferred to B. Existing approaches will either ignore the attack or reverse it. In this paper we introduce a new reduction of preference and attack to defeat, based on the idea that in such a case, instead of ignoring the attack, the preference is ignored. We compare this new reduction with the two existing ones using a principle-based approach, for the four Dung semantics. The principle-based or axiomatic approach is a methodology to choose an argumentation semantics for a particular application, and to guide the search for new argumentation semantics. For this analysis, we also introduce a fourth reduction, and a semantics for preference-based argumentation based on extension selection. Our classification of twenty alternatives for preference-based abstract argumentation semantics using six principles suggests that our new reduction has some advantages over the existing ones, in the sense that if the set of preferences increases, the sets of accepted arguments increase as well. [less ▲]

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See detailAbstract and Concrete Decision Graphs for Choosing Extensions of Argumentation Frameworks
Dauphin, Jérémie UL; Cramer, Marcos UL; van der Torre, Leon UL

in Computational Models of Argument (2018)

Most argumentation semantics allow for multiple extensions, which raises the question of how to choose among extensions. We propose to study this question as a decision problem. Inspired by decision trees ... [more ▼]

Most argumentation semantics allow for multiple extensions, which raises the question of how to choose among extensions. We propose to study this question as a decision problem. Inspired by decision trees commonly used in economics, we introduce the notion of a decision graph for deciding between the multiple extensions of a given AF in a given semantics. We distinguish between abstract decision graphs and concrete instantiations thereof. Inspired by the principle-based approach to argumentation, we formulate two principles that mappings from argumentation frameworks to decision graphs should satisfy, the principles of decision-graph directionality and that of directional decision-making. We then propose a concrete instantiation of decision graphs, which satisfies one of these principles. Finally, we discuss the potential for further research based on this novel methodology. [less ▲]

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See detailArgumentation as Exogenous Coordination
van der Torre, Leon UL; Rienstra, Tjitze; Gabbay, Dov UL

in It's All About Coordination (2018)

Formal argumentation is one of the most popular approaches in modern logic and reasoning. The theory of abstract argumentation introduced by Dung in 1995 has shifted the focus from the internal structure ... [more ▼]

Formal argumentation is one of the most popular approaches in modern logic and reasoning. The theory of abstract argumentation introduced by Dung in 1995 has shifted the focus from the internal structure of arguments to relations among arguments, and temporal dynamics for abstract argumentation was proposed by Barringer, Gabbay and Woods in 2005. In this tradition, we see arguments as reasoning processes, and the interaction among them as a coordination process.We argue that abstract argumentation can adopt ideas and techniques from formal theories of coordination, and as an example we propose a model of sequential abstract argumentation loosely inspired by Reo’s model of exogenous coordination. We show how the argumentation model can represent the temporal dynamics of the liar paradox and predator-prey like behaviour. [less ▲]

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See detailPrioritized norms in formal argumentation
Liao, Beishui; Oren, Nir; van der Torre, Leon UL et al

in Journal of Logic and Computation (2018)

To resolve conflicts amongst norms, various non-monotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent non-monotonic ... [more ▼]

To resolve conflicts amongst norms, various non-monotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent non-monotonic logics. In this paper we propose a representation of prioritized normative reasoning by argumentation. Using hierarchical abstract normative systems (HANS), we define three kinds of prioritized normative reasoning approaches called Greedy, Reduction and Optimization. Then, after formulating an argumentation theory for a HANS, we show that for a totally ordered HANS, Greedy and Reduction can be represented in argumentation by applying the weakest link and the last link principles, respectively, and Optimization can be represented by introducing additional defeats capturing the idea that for each argument that contains a norm not belonging to the maximal obeyable set then this argument should be rejected. [less ▲]

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See detailDetachment in Normative Systems: Examples, inference Patterns, Properties
Parent, Xavier UL; van der Torre, Leon UL

in The IfCoLog Journal of Logics and their Applications (2017), 4(9), 2295-3039

There is a variety of ways to reason with normative systems. This partly reflects a variety of semantics developed for deontic logic, such as traditional semantics based on possible worlds, or alternative ... [more ▼]

There is a variety of ways to reason with normative systems. This partly reflects a variety of semantics developed for deontic logic, such as traditional semantics based on possible worlds, or alternative semantics based on algebraic methods, explicit norms or techniques from non-monotonic logic. This diversity raises the question how these reasoning methods are related, and which reasoning method should be chosen for a particular application. In this paper we discuss the use of examples, inference patterns, and more abstract properties. First, benchmark examples can be used to compare ways to reason with normative systems. We give an overview of several benchmark examples of normative reasoning and deontic logic: van Fraassen’s paradox, Forrester’s paradox, Prakken and Sergot’s cottage regulations, Jeffrey’s disarmament example, Chisholm’s paradox, Makinson’s Möbius strip, and Horty’s priority examples. Moreover, we distinguish various interpretations that can be given to these benchmark examples, such as consistent interpretations, dilemma interpretations, and violability interpretations. Second, inference patterns can be used to compare different ways to reason with normative systems. Instead of analysing the benchmark examples semantically, as it is usually done, in this paper we use inference patterns to analyse them at a higher level of abstraction. We discuss inference patterns reflecting typical logical properties such as strengthening of the antecedent or weakening of the consequent. Third, more abstract properties can be defined to compare different ways to reason with normative systems. To define these more abstract properties, we first present a formal framework around the notion of detachment. Some of the ten properties we introduce are derived from the inference patterns, but others are more abstract: factual detachment, violation detection, substitution, replacements of equivalents, implication, para-consistency, conjunction, factual monotony, norm monotony, and norm induction. We consider these ten properties as desirable for a reasoning method for normative systems. [less ▲]

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See detailMultiagent Deontic Logic and its Challenges from a Normative Systems Perspective
Pigozzi, Gabriella; van der Torre, Leon UL

in The IfCoLog Journal of Logics and their Applications (2017)

This article gives an overview of several challenges studied in deontic logic, with an emphasis on challenges involving agents. We start with traditional modal deontic logic using preferences to address ... [more ▼]

This article gives an overview of several challenges studied in deontic logic, with an emphasis on challenges involving agents. We start with traditional modal deontic logic using preferences to address the challenge of contrary-toduty reasoning, and STIT theory addressing the challenges of non-deterministic actions, moral luck and procrastination. Then we turn to alternative normbased deontic logics detaching obligations from norms to address the challenge of Jørgensen’s dilemma, including the question how to derive obligations from a normative system when agents cannot assume that other agents comply with their norms. We discuss also some traditional challenges from the viewpoint of normative systems: when a set of norms may be termed ‘coherent’, how to deal with normative conflicts, how to combine normative systems and traditional deontic logic, how various kinds of permission can be accommodated, how meaning postulates and counts-as conditionals can be taken into account,how sets of norms may be revised and merged, and how normative systems can be combined with game theory. The normative systems perspective means that norms, not ideality or preference, should take the central position in deontic semantics, and that a semantics that represents norms explicitly provides a helpful tool for analysing, clarifying and solving the problems of deontic logic. We focus on the challenges rather than trying to give full coverage of related work, for which we refer to the handbook of deontic logic and normative systems. [less ▲]

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See detailImplementation of Carmo and Jones Dyadic Deontic Logic in Isabelle/HOL
Benzmüller, Christoph UL; Farjami, Ali UL; Parent, Xavier UL et al

Scientific Conference (2017, July 06)

A shallow semantical embedding of a dyadic deontic logic (by Carmo and Jones) in Isabelle/HOL is presented. First experiments provide evidence that this logic implementation fruitfully enables interactive ... [more ▼]

A shallow semantical embedding of a dyadic deontic logic (by Carmo and Jones) in Isabelle/HOL is presented. First experiments provide evidence that this logic implementation fruitfully enables interactive and automated reasoning at the meta-level the object-level. [less ▲]

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See detailThe pragmatic oddity in a norm-based semantics
Parent, Xavier UL; van der Torre, Leon UL

in Governatori, Guido (Ed.) 16th International Conference on Artificial Intelligence & Law (ICAIL-17) (2017, June)

The ideal worlds of a possible worlds semantics may satisfy both a primary obligation and an associated secondary obligation, for example the obligation to keep a promise and the obligation to apologise ... [more ▼]

The ideal worlds of a possible worlds semantics may satisfy both a primary obligation and an associated secondary obligation, for example the obligation to keep a promise and the obligation to apologise for not keeping it. This is known as the pragmatic oddity introduced by Prakken and Sergot. We argue that an adequate treatment of the pragmatic oddity within a norm-based semantics can be obtained, by not allowing primary and secondary obligations to aggregate, because they are obligations of a di erent kind. On the basis of this conceptual analysis, we introduce two logics, depending on the stance taken on the representation of normative con icts, and we present sound and complete proof systems for these logics. We then give a formal analysis, discuss extensions, and highlight various topics for further research. [less ▲]

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See detailReasoning in Non-probabilistic Uncertainty: Logic Programming and Neural Symbolic Computing as Examples
Besold, Tarek; Garcez, Artur d'Avila; Stenning, Keith et al

in Minds and Machines (2017)

This article aims to achieve two goals: to show that probability is not the only way of dealing with uncertainty (and even more, that there are kinds of uncertainty which are for principled reasons not ... [more ▼]

This article aims to achieve two goals: to show that probability is not the only way of dealing with uncertainty (and even more, that there are kinds of uncertainty which are for principled reasons not addressable with probabilistic means); and to provide evidence that logic-based methods can well support reasoning with uncertainty. For the latter claim, two paradigmatic examples are presented: logic programming with Kleene semantics for modelling reasoning from information in a discourse, to an interpretation of the state of affairs of the intended model, and a neural-symbolic implementation of input/output logic for dealing with uncertainty in dynamic normative contexts. [less ▲]

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See detailCommitments and interaction norms in organisations
Dastani, Mehdi; van der Torre, Leon UL; Yorke-Smith, Neil

in Autonomous Agents & Multi-Agent Systems (2017), 31(2), 207-249

In an organisational setting such as an online marketplace, an entity called the ‘organisation’ or ‘institution’ defines interaction protocols, monitors agent interaction, and intervenes to enforce the ... [more ▼]

In an organisational setting such as an online marketplace, an entity called the ‘organisation’ or ‘institution’ defines interaction protocols, monitors agent interaction, and intervenes to enforce the interaction protocols. The organisation might be a software system that thus regulates the marketplace, for example. In this article we abstract over application-specific protocols and consider commitment lifecycles as generic interaction protocols. We model interaction protocols by explicitly-represented norms, such that we can operationalise the enforcement of protocols by means of norm enforcement, and we can analyse the protocols by a logical analysis of the norms. We adopt insights and methods from commitment-based approaches to agent interaction as well as from norm-based approaches to agent behaviour governance. First, we show how to use explicitly-represented norms to model commitment dynamics (lifecycles). Second, we introduce an operational semantics to operationalise norm enforcement. Third, we show how to logically analyse interaction protocols by means of commitment dynamics and norm enforcement. The model, semantics, and analysis are illustrated by a running example from a vehicle insurance domain. [less ▲]

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See detailThe Principle-Based Approach to Abstract Argumentation Semantics
van der Torre, Leon UL; Vesic, Srdjan

in The IfCoLog Journal of Logics and their Applications (2017)

The principle-based or axiomatic approach is a methodology to choose an argumentation semantics for a particular application, and to guide the search for new argumentation semantics. This article gives a ... [more ▼]

The principle-based or axiomatic approach is a methodology to choose an argumentation semantics for a particular application, and to guide the search for new argumentation semantics. This article gives a complete classification of the fifteen main alternatives for argumentation semantics using the twenty-seven main principles discussed in the literature on abstract argumentation, extending Baroni and Giacomin’s original classification with other semantics and principles proposed in the literature. It also lays the foundations for a study of representation and (im)possibility results for abstract argumentation, and for a principle-based approach for extended argumentation such as bipolar frameworks, preference-based frameworks, abstract dialectical frameworks, weighted frameworks, and input/output frameworks. [less ▲]

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See detailHandling Norms in Multi-Agent System by Means of Formal Argumentation
Peirera, Célia da Costa; Tettamanzi, Andrea G. B.; Villata, Serena et al

in The IfCoLog Journal of Logics and their Applications (2017)

Formal argumentation is used to enrich and analyse normative multi-agent systems in various ways. In this chapter, we discuss three examples from the literature of handling norms by means of formal ... [more ▼]

Formal argumentation is used to enrich and analyse normative multi-agent systems in various ways. In this chapter, we discuss three examples from the literature of handling norms by means of formal argumentation. First, we discuss how existing ways to resolve conflicts among norms using priorities can be represented in formal argumentation, by showing that the so-called Greedy and Reduction approaches can be represented using the weakest and the last link principles respectively. Based on such representation results, formal argumentation can be used to explain the detachment of obligations and permissions from hierarchical normative systems in a new way. Second, we discuss how formal argumentation can be used as a general theory for developing new approaches for normative reasoning, using a dynamic ASPIC-based legal argumentation theory. We show how existing logics of normative systems can be used to analyse such new argumentation systems. Third, we show how argumentation can be used to reason about other challenges in the area of normative multiagent systems as well, by discussing a model for arguing about legal interpretation. In particular, we show how fuzzy logic combined with formal argumentation can be used to reason about the adoption of graded categories and thus address the problem of open texture in normative interpretation. Our aim to discuss these three examples is to inspire new applications of formal argumentation to the challenges of normative reasoning in multiagent systems. [less ▲]

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See detailPrioritized Norms in Formal Argumentation
Liao, Beishui UL; Oren, Nir; van der Torre, Leon UL et al

in Journal of Logic & Computation (2017), abs/1709.08034

To resolve conflicts among norms,various nonmonotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent nonmonotonic logics. In ... [more ▼]

To resolve conflicts among norms,various nonmonotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent nonmonotonic logics. In this paper, we propose a representation of prioritized normative reasoning by argumentation. Using hierarchical abstract normative systems, we define three kinds of prioritized normative reasoning approaches, called Greedy, Reduction, and Optimization. Then, after formulating an argumentation theory for a hierarchical abstract normative system, we show that for a totally ordered hierarchical abstract normative system, Greedy and Reduction can be represented in argumentation by applying the weakest link and the last link principles respectively, and Optimization can be represented by introducing additional defeats capturing implicit conflicts between arguments. [less ▲]

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See detailDefense semantics of argumentation: encoding reasons for accepting arguments
Liao, Beishui UL; van der Torre, Leon UL

E-print/Working paper (2017)

In this paper we show how the defense relation among abstract arguments can be used to encode the reasons for accepting arguments. After introducing a novel notion of defenses and defense graphs, we ... [more ▼]

In this paper we show how the defense relation among abstract arguments can be used to encode the reasons for accepting arguments. After introducing a novel notion of defenses and defense graphs, we propose a defense semantics together with a new notion of defense equivalence of argument graphs, and compare defense equivalence with standard equivalence and strong equivalence, respectively. Then, based on defense semantics, we define two kinds of reasons for accepting arguments, i.e., direct reasons and root reasons, and a notion of root equivalence of argument graphs. Finally, we show how the notion of root equivalence can be used in argumentation summarization. [less ▲]

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See detailProCRob Architecture for Personalized Social Robotics
Ziafati, Pouyan; Rodriguez Lera, Francisco Javier UL; Pinto Costa, Andreia UL et al

Scientific Conference (2017)

For robot tutors, autonomy and personalizations are important factors in order to engage users as well as to personalize the content and interaction according to the needs of individuals. This paper ... [more ▼]

For robot tutors, autonomy and personalizations are important factors in order to engage users as well as to personalize the content and interaction according to the needs of individuals. This paper presents the Programming Cognitive Robot (ProCRob) software architecture to target personalized social robotics in two complementary ways. ProCRob supports the development and personalization of social robot applications by teachers and therapists without computer programming background. It also supports the development of autonomous robots which can adapt according to the human-robot interaction context. ProCRob is based on our previous research on autonomous robotics and has been developed since 2015 by a multi-disciplinary team of researchers from the fields of AI, Robotics and Psychology as well as artists and designers at the University of Luxembourg. ProCRob is currently being used and further developed for therapy of children with autism, and for encouraging rehabilitation activities in patients with post-stroke. This is paper presents a summary of ProCRob and its application in autism. [less ▲]

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See detailRational Enterprise Architecture
van der Torre, Leon UL; Van Zee, Marc UL

in Advances in Artificial Intelligence: From Theory to Practice - 30th International Conference on Industrial Engineering and Other Applications of Applied Intelligent Systems, IEA/AIE 2017, Arras, France, June 27-30, 2017, Proceedings, Part I (2017)

We are interested in formal foundations for enterprise decision support. In this perspective, enterprise architecture is characterised by highly uncertain plans in a changing environment, and translates ... [more ▼]

We are interested in formal foundations for enterprise decision support. In this perspective, enterprise architecture is characterised by highly uncertain plans in a changing environment, and translates strategic goals into an IT strategy. Typically there are a large number of stakeholders with conflicting views, communicating plans of action, and explaining decisions instead of making them. An enterprise architecture considers qualitative before quantitative data, has stronger business focus than other disciplines, and politics, emotions, and soft skills play a bigger role than in other areas. We view a plan abstractly as a sequence of commitments in time, and each commitment in the plan may come with a number of underlying assumptions. If these underlying assumptions change, then parts of the plan may require revision, which in turn may invalidate other parts of the plan, and so on. Therefore, assumptions have an inherently non-monotonic character: they are assumed to be true, unless it becomes clear they are false. This is related to the resource-boundedness of enterprise architecture: an enterprise architect cannot always know all of the assumptions, especially for long term plans. [less ▲]

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