Argumentation Systems (Computer Science)

In computational models of argumentation, argument justification has attracted more attention than statement justification, and significant sensitivity losses are identifiable when dealing with the justification of statements by otherwise appealing formalisms. This paper reappraises statement justification as a formalism-independent component in argument-based reasoning. We introduce a novel general model of argument-based reasoning based on multiple stages of labellings, the last one being devoted to statement justification, identify two alternative paths from argument acceptance to statement justification, and compare their expressiveness. We then show that this model encompasses several prominent literature proposals as special cases, thereby enabling a systematic comparison of existing approaches to statement justification, evidencing their merits and limits. Finally we illustrate our model by specifying a generic ignorance-aware statement justification and showing how it can be seamlessly integrated into different formalisms.

Abduction has been on the back burner in logic programming, as abduction can be too difficult to implement, and costly to perform, in particular if abductive solutions are not tabled. On the other hand, current Prolog systems, with their tabling mechanisms, are mature enough to facilitate the introduction of tabling abductive solutions (tabled abduction) into them. Our contributions are as follows. First, we conceptualize a tabled abduction technique for abductive normal logic programs, permitting abductive solutions to be reused, from one abductive context to another. The approach is underpinned by the theory of ABDUAL and relies on a transformation into tabled logic programs. It particularly makes use of the dual transformation of ABDUAL that enables efficiently handling the problem of abduction under negative goals, by introducing dual positive counterparts for them. Second, we realize this tabled abduction technique in TABDUAL, a system implemented in XSB Prolog. The implementat...

This paper reports on our work for defining a methodology for applying energy and other polices into smart buildings that use Internet of Things enabled devices. The goal is to automate decisions on a variety of issues where there is a conflict of policies between the priorities of different users and roles. We use computational argumentation and a method for compiling meta-policies to automate the decision-making process with the capability to offer human-readable explanations and, at the same time, to achieve increased energy efficiency. IoT sensors take the necessary measurements and data using the KNX standard. To validate our methodology we used an energy related scenario. The case study is applied on a building in the Technical University of Crete, where there are suitable sensors for measuring basic parameters (or data), such as temperature, lighting conditions, motion, and, carbon dioxide levels. The building's energy consumption data is imported by the Open Studio/Energy plus application. A web-based service for hierarchical argumentation, Gorgias Cloud, is used to process the data and make decisions.

The current implementation provides a demonstration of a number of basic argumentation components that can be applied in the context of multi-agent systems. These components include algorithms for calculating argumentation semantics, as well as for determining the justification status of the arguments and providing explanation in the form of formal discussion games. Furthermore, the current demonstrator also includes the first implementation we know of regarding argument-based judgment aggregation theory.

Gorgias Cloud offers argumentation-based decision making as a service. The service includes an integrated development environment for the theories, testing and execution based on user scenarios, and, finally, an API for use by user applications. Gorgias is a structured argumentation framework where arguments are constructed using a basic scheme of argument rules. Two types of arguments are constructed within a Gorgias argumentation theory: object-level arguments and priority arguments expressing a preference between other arguments. Admissible composite arguments supporting a claim typically include both types of arguments. The Gorgias framework was introduced in [1], extended in [2] and applied to a variety of real-life application problems in [3]. The Gorgias system allows us to code argumentation theories of the form described above and subsequently query the system to find out if there is an admissible (composite) argument that supports a desired Claim. The system of Gorgias has been publicly available since 2003 and has been used by several research groups to develop prototype real-life applications of argumentation in a variety of application domains. Today, it is available as a service over the internet with Gorgias Cloud, which provides an integrated environment for developing applications of argumentation with three novel features:

We present a new priority-based approach to reasoning with specificity which subsumes inheritance reasoning. The new approach differs from other priority-based approaches in the literature in the way priority between defaults is handled. Here, it is conditional rather than unconditional as in other approaches. We show that any unconditional handling of priorities between defaults as advocated in the literature until now is not sufficient to capture general defeasible inheritance reasoning. We propose a simple and novel argumentation semantics for reasoning with specificity taking the conditionality of the priorities between defaults into account. Since the proposed argumentation semantics is a form of stable semantics of nonmonotonic reasoning, it inherits a common problem of the latter where it is not always defined for every default theory. We propose a class of stratified default theories for which the argumentation semantics is always defined. We also show that acyclic and consistent inheritance networks are stratified. We prove that the argumentation semantics satisfies the basic properties of a nonmonotonic consequence relation such as deduction, reduction, conditioning, and cumulativity for well-defined and stratified default theories. We give a modular and polynomial transformation of default theories with specificity into semantically equivalent Reiter default theories.

This book represents the conclusion of ten years of research into dissociation. The results of this research have been published, bit by bit, in various media: journals, conference proceedings, anthologies. This monograph brings together these scattered papers. For this book, the papers have been rewritten, new material has been added, and the various parts have been grouped into a coherent whole. I want to thank my colleagues in the Department of Speech Communication, Argumentation Theory, and Rhetoric of the Universiteit van Amsterdam most warmly for the critical and constructive comments that I have been so fortunate as to receive during all these years. Without the intellectual stimulus of the discussions with Frans van Eemeren, Peter Houtlosser (who, to my intense regret, did not live to see the appearance of this book), Francisca Snoeck Henkemans, Bart Garssen, Eveline Feteris, Jan-Albert van Laar, Jean Wagemans, and the other participants in the Friday research symposia in our Department, I would not have been able to deal with the complex problems that the various aspects of dissociation all too often posed. My gratitude also extends to the Amsterdam School for Cultural Analysis, particularly for the travel grants I was awarded, which made it possible for me to also submit the results of my research to the critical scrutiny of the international forum of argumentation scholars. Finally, I want to thank the two anonymous referees who read the manuscript of this book for their many useful suggestions for improvement.

In Context' is aimed at giving contextualization its rightful place in the study of argumentation. First, Frans H. van Eemeren explains the crucial role of context in a reconstructive analysis of argumentative discourse. He distinguishes four levels of contextualization. Second, he situates his approach to context in the field of argumentation studies by comparing it with Walton's approach. He emphasizes the importance of distinguishing clearly between a normatively motivated theoretical ideal model and empirically-based communicative activity types. Third, van Eemeren concentrates on the 'macro-level' of contextualization: contextualization in institutionalized communicative activity types. He makes clear that the macro-context of a communicative activity type can be characterized argumentatively by describing the disctinctive features of the empirical counterparts of the four stages of a critical discussion in the activity type concerned. Fourth, he points out what the consequences of the macrocontextualization of argumentative discourse in a certain communicative activity type are for the strategic maneuvering that may takes place and the identification of fallacies as derailments of strategic maneuvering. Fifth, van Eemeren draws some general conclusions regarding the role of contextualization in the analysis and evaluation of argumentative discourse.

This paper reports on a program for the development of cognitive systems based on user specifications expressed in Natural Language in the form of high-level guidelines for the desired behaviour of those systems. Language analysis from existing NLP tools is used to generate scenarios based on the users’ description of their preferences in the provision of the service by the system. These scenarios are combined with the SoDA Methodology to develop and generate an argumentation theory that captures the guidelines of operation given in the natural language description of the user. The intended architecture of a fully automated system that generates argumentation based cognitive systems from natural language is presented, together with a first analysis of the challenges posed and evaluation of progress in addressing them. This system is called Gorgias-NL, reflecting the central task of the approach to provide a natural language interface to the Gorgias argumentation system.

It can be argued that linguistic aspects of argumentation have attracted scholarly attention ever since the foundation of rhetoric, which originally developed as the study of means of persuasion, and thus, to a fair extent, that linguistics plays an important role in the study of argumentation at large [...]

Gorgias Cloud offers argumentation-based decision making as a service. The service includes an integrated development environment for the theories, testing and execution based on user scenarios, and, finally, an API for use by user applications. Gorgias is a structured argumentation framework where arguments are constructed using a basic scheme of argument rules. Two types of arguments are constructed within a Gorgias argumentation theory: object-level arguments and priority arguments expressing a preference between other arguments. Admissible composite arguments supporting a claim typically include both types of arguments. The Gorgias framework was introduced in [1], extended in [2] and applied to a variety of real-life application problems in [3]. The Gorgias system allows us to code argumentation theories of the form described above and subsequently query the system to find out if there is an admissible (composite) argument that supports a desired Claim. The system of Gorgias has been publicly available since 2003 and has been used by several research groups to develop prototype real-life applications of argumentation in a variety of application domains. Today, it is available as a service over the internet with Gorgias Cloud, which provides an integrated environment for developing applications of argumentation with three novel features:

This paper reports on a program for the development of cognitive systems based on user specifications expressed in Natural Language in the form of high-level guidelines for the desired behaviour of those systems. Language analysis from existing NLP tools is used to generate scenarios based on the users’ description of their preferences in the provision of the service by the system. These scenarios are combined with the SoDA Methodology to develop and generate an argumentation theory that captures the guidelines of operation given in the natural language description of the user. The intended architecture of a fully automated system that generates argumentation based cognitive systems from natural language is presented, together with a first analysis of the challenges posed and evaluation of progress in addressing them. This system is called Gorgias-NL, reflecting the central task of the approach to provide a natural language interface to the Gorgias argumentation system.

Recursive argumentation frameworks (RAF) take into account the notion of higher-order attacks. Their semantics are defined in terms of structures. A labelling version of these semantics is defined in this report, and their correspondence with structures is shown. The case of RAF with no recursive attacks is considered, confirming that RAF are a generalization of Dung's argumentation frameworks. A semantics which had not been considered so far for RAF, the eager semantics, is in addition introduced.

This paper presents the past and present efforts of developing real-life applications of argumentation with the Gorgias preference-based structured argumentation framework of Logic Programming with Priorities. Since its free availability on the web in 2003, the Gorgias system has been used by different groups in a variety of real-life applications in areas such as medical support, network security, business computing, ambient intelligence and, recently, in the area of cognitive personal assistants. We briefly review the Gorgias framework and its past applications and present an emerging general methodological approach for developing "decision making" applications of argumentation. This approach allows the development of real world applications directly from their high-level requirements expressed in the language of the application without the need for familiarity with the underlying technical details of argumentation. A new tool, called Gorgias-B, supports this high-level development of applications and automatically generates the underlying argumentation theory in Gorgias code. The paper also reports on ongoing real-life applications in two domains: an eye-clinic assistant for first level support, and systems for patient data access and data sharing agreements according to the relevant legislation and contracts or policies of the several stakeholders involved. The proposed approach is quite general for this type of applications of argumentation and, thus, it can be used with any preference-based argumentation framework.

In the paper, a model of debate is developed which includes a model of argument. When starting interaction, the participants have opposite communicative goals. They are exchanging arguments and counter-arguments and one of them has finally to abandon his or her initial communicative goal, i.e. one participant 'wins' and another 'loses'. An analysis of human-human dialogue corpus is carried out in order to evaluate the suitability of the model for describing natural debates. A computer implementation is introduced. Notions of negotiation, debate and argument are discussed.

In this paper we introduce a novel family of semantics called weakly complete semantics. Differently from Dung's complete semantics, weakly complete semantics employs a mechanism called undecidedness blocking by which the label undecided of an attacking argument is not always propagated to an otherwise accepted attacked argument. The new semantics are conflict-free, non-admissible but employing a weaker notion of admissibility; they allow reinstatement and they retain the majority of properties of complete semantics. We show how both weakly complete and Dung's complete semantics can be generated by applying different undecidedness blocking strategies, making undecidedness blocking a unifying mechanism underlying argumentation semantics. The semantics are also an example of ambiguity blocking Dunganian semantics and the first semantics to tackle the problem of self-defeating attacking arguments. In the last part of the paper we compare weakly complete semantics with the recent work of Baumann et al. on weakly admissible semantics. Since the two families of semantics do not coincide, a principlebased analysis of the two approaches is provided. The analysis shows how our semantics satisfy a number of principles satisfied by Dung's complete semantics but not by Baumann et al. semantics, including directionality, abstention, SCC-decomposability and cardinality of extensions, making them a more faithful non-admissible version of Dung' semantics.

A macroscope is proposed and tested here for the discovery of the unique argumentative footprint that characterizes how a collective (e.g., group, online community) manages differences and pursues disagreement through argument in a polylogue. The macroscope addresses broader analytic problems posed by various conceptualizations of large-scale argument, such as fields, spheres, communities, and institutions. The design incorporates a two-tier methodology for detecting argument patterns of the arguments performed in arguing by an interactive collective that produces views, or topographies, of the ways that issues are generated in the making and defending of standpoints. The design premises for the macroscope build on insights about argument patterns from pragma-dialectical theory by incorporating research and theory on disagreement management and the Argumentum Model of Topics. The design reconceptualizes prototypical and stereotypical argument patterns for characterizing large-scale argumentation. A prototype of the macroscope is tested on data drawn from six threads about oil-drilling and fracking from the subreddit Changemyview. The implementation suggests the efficacy of the macroscope's design and potential for identifying what communities make controversial and how the disagreement space in a polylogue is managed through stereotypical argument patterns in terms of claims/premises, inferential relations, and presentational devices.

When integrating data coming from multiple different sources we are faced with the possibility of incon-sistency in databases. A paraconsistent approach for knowledge base integration allows keeping inconsistent information and reasoning in its presence. In this paper, we use a paraconsistent logic (LFI1) as the underly-ing logic for the specification of P-Datalog, a deductive query language for databases containing inconsistent in-formation. We present a declarative semantics which captures the desired meaning of a recursive query exe-cuted over a database containing inconsistent facts and whose rules allow infering information from inconsis-tent premises. We also present a bottom-up evaluation method for P-Datalog programs based on an alternating fixpoint operator.

In the current paper, we reexamine the connection between abstract argumentation and assumption-based argumentation. These two formalisms are often claimed to be equivalent in the sense that (a) evaluating an assumption based argumentation framework directly with the dedicated semantics, and (b) first constructing the corresponding abstract argumentation framework and then applying the corresponding abstract argumentation semantics, produce the same outcome. Although this holds for several semantics, in this work we show that there exist well-studied admissibility-based semantics (semi-stable and eager) under which equivalence does not hold.

Dung's argumentation frameworks have been applied for over twenty years to the analysis of argument justification. This representation focuses on arguments and the attacks among them, abstracting away from other features like the internal structure of arguments, the nature of utterers, the specifics of the attack relation, etc. The model is highly attractive because it reduces most of the complexities involved in argumentation processes. It can be applied to different settings, like the argument evaluation of an individual agent or the case of dialectic disputes between two agents (pro and con), or even in multi-agent collective argumentation. The latter case involves agents with possibly different arguments and/or opinions on how to evaluate them, leading to the possibility of considering multiple sets of arguments and attack relations. Two basic questions can be asked here, namely 'what to aggregate' and 'how to aggregate'. The former concerns what kinds of entities do the agents intend to choose (arguments, attacks, assessments, etc.), while the second one focuses on which aggregation mechanisms yield rational choices (voting on arguments, merging procedures to obtain a common argumentation framework, deliberation processes, etc.). In particular, the question about the rationality of a collective argument choice relates this topic to Social Choice and Judgment Aggregation theories, while its associated strategic issues relate it to Game Theory. The research efforts on the disparate problems elicited by collective argumentation have generated a considerable corpus of literature that deserves an orderly evaluation. This survey is intended as a contribution to that end.

Dung's argumentation frameworks have been applied for over twenty years to the analysis of argument justification. This representation focuses on arguments and the attacks among them, abstracting away from other features like the internal structure of arguments, the nature of utterers, the specifics of the attack relation, etc. The model is highly attractive because it reduces most of the complexities involved in argumentation processes. It can be applied to different settings, like the argument evaluation of an individual agent or the case of dialectic disputes between two agents (pro and con), or even in multi-agent collective argumentation. The latter case involves agents with possibly different arguments and/or opinions on how to evaluate them, leading to the possibility of considering multiple sets of arguments and attack relations. Two basic questions can be asked here, namely 'what to aggregate' and 'how to aggregate'. The former concerns what kinds of entities do the agents intend to choose (arguments, attacks, assessments, etc.), while the second one focuses on which aggregation mechanisms yield rational choices (voting on arguments, merging procedures to obtain a common argumentation framework, deliberation processes, etc.). In particular, the question about the rationality of a collective argument choice relates this topic to Social Choice and Judgment Aggregation theories, while its associated strategic issues relate it to Game Theory. The research efforts on the disparate problems elicited by collective argumentation have generated a considerable corpus of literature that deserves an orderly evaluation. This survey is intended as a contribution to that end.

Part of the idea of this thesis originated during a lecture of Arno Lodder at the Vereniging Voor Logica (VVL). To me, the idea of a mathematical description of what rational dialogue or argumentation should look like sounded very appealing. I then studied a number of formalisms in this field, but to my surprise, the informal kinds of dialogues that I observed around me often turned out to have a totally different structure and nature than what was specified by the various dialectical formalisms. It is this deviation that inspired me to write this thesis. There are a few people who directly or indirectly contributed to this thesis that I would like to thank. First of all, there is my promotor, Reind van de Riet, who despite the fact that I moved out of his field of expertise continued to support me. Furthermore, I would like to thank my copromotor, Henry Prakken, for it is his advice that helped to give the thesis its current form. Much informal input has also been gathered by carefully examining the various of discussions that took place during lunch and coffee time, at which Jan Broersen, Radu Serban, Mehdi Dastani and Joris Hulstijn participated. Special thanks go to Leon van der Torre, who also helped to develop a formal account of the original idea. Also very helpful was a discussion with Gerard Vreeswijk. His warning about "hacking", or tuning a particular formalism so that a certain desirable outcome is obtained resulted in an extensive treatment of criteria for the construction of logical formalisms. Last, but not least, I would like to thank Jan-Willem Klop for his support during the difficult last months of writing this thesis. Although the process of producing this thesis has been a difficult one, I hope the result will be worth reading. v vi 6 Summary and conclusions Epilogue Samenvatting SIKS Dissertation Series 3 Here, "⇒" stands for defeasible implication and "⊃" stands for material implication. 4 The symbol |∼ stands for nonmonotonic derivability.

Structured argumentation is a family of formal approaches for the handling of defeasible, potentially inconsistent information. Many models for structured argumentation distinguish between strict and defeasible inference rules. Defeasible rules often come with varying degrees of strength which is formally represented by a preorder over the defeasible rules. Various lifting principles have been presented in the literature to determine the relative strength of an argument by considering the strength of the defeasible rules used in its construction. The strength of arguments then comes into play when determining whether an attack (a purely syntactic relationship between arguments) results in a defeat (i.e. a successful attack). In \citecaminada2007evaluation,Wu2012, several rationality postulates were proposed that serve as a measure to assess the normative rationality of structured argumentation formalisms. In \citeheyninck2017revisiting, the first formalism satisfying all rationality...

Dung's abstract theory of argumentation has become established as a general framework for various species of non-monotonic reasoning, and reasoning in the presence of conflict. A Dung framework consists of arguments related by attacks, and the extensions of a framework, and so the status of arguments, are defined under different semantics. Developments of Dung's work have also defined argument labellings as an alternative way of characterising extensions, and dialectical argument game proof theories for establishing the status of individual arguments. Recently, Extended Argumentation Frameworks extend Dung's theory so that arguments not only attack arguments, but attacks themselves. In this way, the extended theory provides an abstract framework for principled integration of meta-level argumentation about defeasible preferences applied to resolve conflicts between object level arguments. In this paper we formalise labellings and argument games for a selection of Dung's semantics defined for the extended frameworks.

The field of computational models of argument aims to provide support for automated reasoning through algorithms that operate on arguments and attack relations between them. In this paper we present a new labelling algorithm that lists all preferred extensions of an abstract argumentation framework. The new algorithm is enhanced by a new pruning strategy. We verified our new labelling algorithm and showed that it enumerates preferred extensions faster than the old labelling algorithm.

A Dung argumentation framework (AF) is a pair (A,R): A is a set of abstract arguments and R ⊆ A×A is a binary relation, so-called the attack relation, for capturing the conflicting arguments. Labeling based algorithms for enumerating extensions (i.e. sets of acceptable arguments) have been set out such that arguments (i.e. elements of A) are the only subject for labeling. In this paper we present implemented algorithms for listing extensions by labeling attacks (i.e. elements of R) along with arguments. Specifically, these algorithms are concerned with enumerating all extensions of an AF under a number of argumentation semantics: preferred, stable, complete, semi stable, stage, ideal and grounded. Our algorithms have impact, in particular, on enumerating extensions of AF-extended models that allow attacks on attacks. To demonstrate this impact, we instantiate our algorithms for an example of such models: namely argumentation frameworks with recursive attacks (AFRA), thereby we end u...

We present a new priority-based approach to reasoning with specificity which subsumes inheritance reasoning. The new approach differs from other priority-based approaches in the literature in the way priority between defaults is handled. Here, it is conditional rather than unconditional as in other approaches. We show that any unconditional handling of priorities between defaults as advocated in the literature until now is not sufficient to capture general defeasible inheritance reasoning. We propose a simple and novel argumentation semantics for reasoning with specificity taking the conditionality of the priorities between defaults into account. Since the proposed argumentation semantics is a form of stable semantics of nonmonotonic reasoning, it inherits a common problem of the latter where it is not always defined for every default theory. We propose a class of stratified default theories for which the argumentation semantics is always defined. We also show that acyclic and consistent inheritance networks are stratified. We prove that the argumentation semantics satisfies the basic properties of a nonmonotonic consequence relation such as deduction, reduction, conditioning, and cumulativity for well-defined and stratified default theories. We give a modular and polynomial transformation of default theories with specificity into semantically equivalent Reiter default theories.

In the current paper, we reexamine the connection between formal argumentation and logic programming from the perspective of semantics. We observe that one particular translation from logic programs to instantiated argumentation (the one described by Wu, Caminada and Gabbay) is able to serve as a basis for describing various equivalences between logic programming semantics and argumentation semantics. In particular, we are able to provide a formal connection between regular semantics for logic programming and preferred semantics for formal argumentation. We also show that there exist logic programming semantics (L-stable semantics) that cannot be captured by any abstract argumentation semantics.

The purpose of this paper is to study the fundamental mechanism, humans use in argumentation, and to explore ways to implement this mechanism on computers. We do so by first developing a theory for argumentation whose central notion is the acceptability of arguments. Then we argue for the "correctness" or "appropriateness" of our theory with two strong arguments. The first one shows that most of the major approaches to nonmonotonic reasoning in AI and logic programming are special forms of our theory of argumentation. The second argument illustrates how our theory can be used to investigate the logical structure of many practical problems. This argument is based on a result showing that our theory captures naturally the solutions of the theory of n-person games and of the well-known stable marriage problem. By showing that argumentation can be viewed as a special form of logic programming with negation as failure, we introduce a general logic-programming-based method for generating meta-interpreters for argumentation systems, a method very much similar to the compiler-compiler idea in conventional programming.

This paper compares an international two-index model to an International Arbitrage Pricing Theory (IAPT) two-factor model to evaluate the performance of 37 U.S.-based international mutual funds over the 1985-1993 period. Results from the index model confirm prior research that international funds perlorm as well as the market proxy. In contrast, the IAPT model implies superior investment performance by the international funds. Moreover, the two models produce different relative performance rankings. Intertemporal comparisons of the models indicate that the multifactor IAPT model better reflects the international equity return-generating process.

We present a new priority-based approach to reasoning with specificity which subsumes inheritance reasoning. The new approach differs from other priority-based approaches in the literature in the way priority between defaults is handled. Here, it is conditional rather than unconditional as in other approaches. We show that any unconditional handling of priorities between defaults as advocated in the literature until now is not sufficient to capture general defeasible inheritance reasoning. We propose a simple and novel argumentation semantics for reasoning with specificity taking the conditionality of the priorities between defaults into account. Since the proposed argumentation semantics is a form of stable semantics of nonmonotonic reasoning, it inherits a common problem of the latter where it is not always defined for every default theory. We propose a class of stratified default theories for which the argumentation semantics is always defined. We also show that acyclic and consistent inheritance networks are stratified. We prove that the argumentation semantics satisfies the basic properties of a nonmonotonic consequence relation such as deduction, reduction, conditioning, and cumulativity for well-defined and stratified default theories. We give a modular and polynomial transformation of default theories with specificity into semantically equivalent Reiter default theories.

In today's 'networked' public sphere, arguers are faced with countless controversies roaming out there. Knowing what is at stake at any point in time, and keeping under control the contribution one's arguments make to the different interrelated issues requires careful craft (e.g. Mohammed and Zarefsky, in Feteris, Garssen and Snoeck Henkemans (eds) Keeping in touch with Pragma-Dialectics. In honor of Frans H. van Eemeren. John Benjamins, Amsterdam, 2011). In this paper, I explore the difficulty of determining what is at stake at any moment of the argumentative situation and explore the challenge that that creates for examining the strategic shape of arguments. I argue that a meaningful examination of networked argumentative encounters requires that the boundaries of an encounter remain 'fluid. In dealing with the fluid boundaries, I suggest to identify "argumentative associates" and "standing standpoints".

In this paper, I critically examine the main accounts of goals in argumentative discourse, aiming to formulate an account that is suitable for the examination of public political arguments, where typically multiple legitimate goals are pursued simultaneously. Such arguments are viewed as contributions to what can be dialectically reconstructed as multiple simultaneous discussions, and are analysed as strategic manoeuvres that can under certain conditions be reasonable but may, if such conditions are violated, become fallacious.

The ASPIC + framework is intermediate in abstraction between Dung's argumentation framework and concrete instantiating logics. This paper generalises ASPIC + to accommodate classical logic instantiations, and adopts a new proposal for evaluating extensions: attacks are used to define the notion of conflict-free sets, while the defeats obtained by applying preferences to attacks, are exclusively used to determine the acceptability of arguments. Key properties and rationality postulates are then shown to hold for the new framework.

The ASPIC + framework is intermediate in abstraction between Dung's argumentation framework and concrete instantiating logics. This paper generalises ASPIC + to accommodate classical logic instantiations, and adopts a new proposal for evaluating extensions: attacks are used to define the notion of conflict-free sets, while the defeats obtained by applying preferences to attacks, are exclusively used to determine the acceptability of arguments. Key properties and rationality postulates are then shown to hold for the new framework.

Bipolar Argumentation Frameworks (BAFs) are an important class of argumentation frameworks useful for capturing, reasoning with, and deriving conclusions from debates. They have the potential to make solid contributions to real-world multi-agent systems and human-agent interaction in domains such as legal reasoning, healthcare and politics. Despite this fact, practical systems implementing BAFs are largely lacking. In this demonstration, we provide a software system implementing novel algorithms for calculating extensions (winning sets of arguments) of BAFs. Participants in the demonstration will be able to input their own debates into our system, and watch a graphical representation of the algorithms as they process information and decide which sets of arguments are winners of the debate.

Whilst computational argumentation and computational explanation have both been studied intensively in AI, models that incorporate both types of reasoning are only just starting to emerge. The two forms of reasoning need to be clearly distinguished, as they may influence dialogue protocol and strategy. We show that this distinction can be made by considering the speech acts used to put forth the reasoning structures. Using the language of the Argument Interchange Format, ideas from speech act theory are integrated into a conceptual model that allows us to perform both argumentative and explanatory reasoning.

In the current paper, we reexamine the connection between formal argumentation and logic programming from the perspective of semantics. We observe that one particular translation from logic programs to instantiated argumentation (the one described by Wu, Caminada and Gabbay) is able to serve as a basis for describing various equivalences between logic programming semantics and argumentation semantics. In particular, we are able to provide a formal connection between regular semantics for logic programming and preferred semantics for formal argumentation. We also show that there exist logic programming semantics (L-stable semantics) that cannot be captured by any abstract argumentation semantics.

Argumentative debates are a powerful tool for resolving conflicts and reaching agreements in open environments such as on-line communities. Here we introduce an argumentation framework to structure argumentative debates. Our framework represents the arguments issued by the participants involved in a debate, the (attack and defence) relationships between them, as well as participants' opinions on them. Furthermore, we tackle the problem of computing a collective decision from participants' opinions. With this aim, we design an aggregation function to ensure that participants reach a coherent collective decision.

Argumentation-based debates are mechanisms that a group can use to resolve conflicting opinions and hence reach agreement. They have many potential applications in on-line communities and other open environments. In this paper, we provide computational infrastructure to support argumentation-based debates, in particular focusing on the problem of how participants in a debate can reach agreement about the outcome of the debate, given all the statements that have been made. Our approach makes it possible to represent arguments that are put forward by the participants in a debate, allows both positive and negative relationships between the arguments to be represented, and makes it possible for participants to express opinions about both the arguments and the outcome of the debate. Our main contribution is to provide a novel method-indeed the first method-for computing the collective decision that emerges from the combination of a set of arguments and a set of opinions about whether the arguments hold or not. To do this, we carry out a formal investigation of a family of aggregation functions. This family starts with a function that is firmly rooted in the social choice literature, and is extended with functions that are more oriented towards the use of argumentation. We prove that to ensure that the collective decision is coherent, a property that we think is essential, an aggregation function needs to take into account the dependencies between arguments. We also provide an empirical analysis of the performance of our approach to reaching a collective decision, showing that a collective decision can be reached for debates, of the size that one currently finds online, in reasonable time.

This paper uses argumentation as the basis for modeling and implementing the relevant legislation of an EU country relating to medical data access. Users can consult a web application for determining their allowed level of access to a patient's medical record and are offered an explanation based on the relevant legislation. The system can also advise a user on what additional information is required for a higher access level. The system is currently in the process of an extensive evaluation through a pilot trial with a special focus group of medical professionals. The development methodology that we have used is generally applicable to any other similar cases of decision making based on legislative regulations. The main advantage of using argumentation is the ability to explain the solutions drawn and the high modularity of software facilitating the extension and adaptation of the system when new relevant legislation becomes available.

An argumentation framework can be seen as expressing, in an abstract way, the conflicting information of an underlying logical knowledge base. This conflicting information often allows for the presence of more than one possible reasonable position (extension/labelling) which one can take. A relevant question, therefore, is how much these positions differ from each other. In the current paper, we will examine the issue of how to define meaningful measures of distance between the (complete) labellings of a given argumentation framework. We provide concrete distance measures based on argument-wise label difference, as well as based on the notion of critical sets, and examine their properties.

On the Web, there is always a need to aggregate opinions from the crowd (as in posts, social networks, forums, etc.). Different mechanisms have been implemented to capture these opinions such as Like in Facebook, Favorite in Twitter, thumbs-up/-down, flagging, and so on. However, in more contested domains (e.g., Wikipedia, political discussion, and climate change discussion), these mechanisms are not sufficient, since they only deal with each issue independently without considering the relationships between different claims. We can view a set of conflicting arguments as a graph in which the nodes represent arguments and the arcs between these nodes represent the defeat relation. A group of people can then collectively evaluate such graphs. To do this, the group must use a rule to aggregate their individual opinions about the entire argument graph. Here we present the first experimental evaluation of different principles commonly employed by aggregation rules presented in the literat...

We define abstract proof procedures for performing credulous and sceptical non-monotonic reasoning, with respect to the argumentation-theoretic formulation of non-monotonic reasoning proposed in [1]. Appropriate instances of the proposed proof procedures provide concrete proof procedures for concrete formalisms for non-monotonic reasoning, for example logic programming with negation as failure and default logic. We propose (credulous and sceptical) proof procedures under different argumentation-theoretic semantics, namely the conventional stable model semantics and the more liberal partial stable model or preferred extension semantics. We study the relationships between proof procedures for different semantics, and argue that, in many meaningful cases, the (simpler) proof procedures for reasoning under the preferred extension semantics can be used as sound and complete procedures for reasoning under the stable model semantics. In many meaningful cases still, proof procedures for credulous reasoning under the preferred extension semantics can be used as (much simpler) sound and complete procedures for sceptical reasoning under the preferred extension semantics. We compare the proposed proof procedures with existing proof procedures in the literature.

Better use of biomedical knowledge is an increasingly pressing concern for tackling challenging diseases and for generally improving the quality of healthcare. The quantity of biomedical knowledge is enormous and it is rapidly increasing. Furthermore, in many areas it is incomplete and inconsistent. The development of techniques for representing and reasoning with biomedical knowledge is therefore a timely and potentially valuable goal. In this paper, we focus on an important and common type of biomedical knowledge that has been obtained from clinical trials and studies. We aim for (1) a simple language for representing the results of clinical trials and studies; (2) transparent reasoning with that knowledge that is intuitive and understandable to users; and (3) simple computation mechanisms with this knowledge in order to facilitate the development of viable implementations. Our approach is to propose a logical language that is tailored to the needs of representing and reasoning with the results of clinical trials and studies. Using this logical language, we generate arguments and counterarguments for the relative merits of treatments. In this way, the incompleteness and inconsistency in the knowledge is analysed via argumentation. In addition to motivating and formalising the logical and argumentation aspects of the framework, we provide algorithms and computational complexity results.