Abstract argumentation systems

In this paper, we develop a theory of abstract argumentation systems. An abstract argumentation system is a collection of “defeasible proofs”, called arguments, that is partially ordered by a relation expressing the difference in conclusive force. The prefix “abstract” indicates that the theory is concerned neither with a specification of the underlying language, nor with the development of a subtheory that explains the partial order. An unstructured language, without logical connectives such as negation, makes arguments not (pairwise) inconsistent, but (groupwise) incompatible. Incompatibility and difference in conclusive force cause defeat among arguments. The aim of the theory is to find out which arguments eventually emerge undefeated. These arguments are considered to be in force. Several results are established. The main result is that arguments that are in force are precisely those that are in the limit of a so-called complete argumentation sequence.     

Extending abstract argumentation systems theory

In this paper, we extend the theory of abstract argumentation systems proposed by Vreeswijk (1997). This framework stands at a high abstraction level and provides a general model for argumentation activity. However, the theory reveals an inherent limitation in that the premises of the argumentation process are assumed to be indefeasible, and this introduces the need of an implicit constraint on the strength of the arguments, in order to preserve correctness. In many application contexts the information available to start reasoning is not guaranteed to be completely reliable, therefore it is natural to assume that premises can be discarded during the argumentation process. We extend the theory by admitting that premises can be defeated and relaxing the implicit assumption about their strength.Besides fixing the technical problems related to this hidden assumption (e.g., ensuring that warranted arguments are compatible), our proposal provides an integrated model for belief revision and defeasible reasoning, confirming the suitability of argumentation as a general model for the activity of intelligent reasoning in presence of various kinds of uncertainty.     

Twelve theses on argumentation systems

In this article we consider the partition of a set of statements P = P ^a ∪ P ^b ∪ P′, where P ^a , P ^b , P′ are, correspondingly, sets of statements only being argumented, both being argumented and argumenting, and only argumenting (basic statements). On P are defined two functions of argument and counter-argument selection forming the semantics for logics of argumentation. A four-valued logic of argumentation is proposed. By means of graph theory are formed trees of arguments (argument trees), wood, consisting of them, and some transformations of the wood, such that their result may be both planar and non-planar graph. Argument systems (systems of arguments) are defined together with their characterizations that use analytic tableaux. With the help of argument trees a specification of the idea of hermeneutic (“vicious”) circle is formalized.     

On the evaluation of argumentation formalisms

Argumentation theory has become an important topic in the field of AI. The basic idea is to construct arguments in favor and against a statement, to select the “acceptable” ones and, finally, to determine whether the original statement can be accepted or not. Several argumentation systems have been proposed in the literature. Some of them, the so-called rule-based systems, use a particular logical language with strict and defeasible rules. While these systems are useful in different domains (e.g. legal reasoning), they unfortunately lead to very unintuitive results, as is discussed in this paper. In order to avoid such anomalies, in this paper we are interested in defining principles, called rationality postulates, that can be used to judge the quality of a rule-based argumentation system. In particular, we define two important rationality postulates that should be satisfied: the consistency and the closure of the results returned by that system. We then provide a relatively easy way in which these rationality postulates can be warranted for a particular rule-based argumentation system developed within a European project on argumentation.     

Formalizing value-guided argumentation for ethical systems design

The persuasiveness of an argument depends on the values promoted and demoted by the position defended. This idea, inspired by Perelman’s work on argumentation, has become a prominent theme in artificial intelligence research on argumentation since the work by Hafner and Berman on teleological reasoning in the law, and was further developed by Bench-Capon in his value-based argumentation frameworks. One theme in the study of value-guided argumentation is the comparison of values. Formal models involving value comparison typically use either qualitative or quantitative primitives. In this paper, techniques connecting qualitative and quantitative primitives recently developed for evidential argumentation are applied to value-guided argumentation. By developing the theoretical understanding of intelligent systems guided by embedded values, the paper is a step towards ethical systems design, much needed in these days of ever more pervasive AI techniques.     

Dynamics of argumentation systems: A division-based method

The changing of arguments and their attack relation is an intrinsic property of a variety of argumentation systems. So, it is very important to efficiently figure out how the status of arguments in a system evolves when the system is updated. However, unlike other areas of argumentation that have been deeply explored, such as argumentation semantics, proof theories, and algorithms, etc., dynamics of argumentation systems has been comparatively neglected. In this paper, we formulate a general theory (called a division-based method) to cope with this problem based on a new concept: the division of an argumentation framework. When an argumentation framework is updated, it is divided into three parts: an unaffected, an affected, and a conditioning part. The status of arguments in the unaffected sub-framework remains unchanged, while the status of the affected arguments is computed in a special argumentation framework (called a conditioned argumentation framework, or briefly CAF) that is composed of an affected part and a conditioning part. We have proved that under a certain semantics that satisfies the directionality criterion (complete, preferred, ideal, or grounded semantics), the extensions of the updated framework are equal to the result of a combination of the extensions of an unaffected sub-framework and sets of the extensions of a set of assigned CAFs. Due to the efficiency of the division-based method, it is expected to be very useful in various kinds of argumentation systems where arguments and attacks are dynamics.     

On merging software extensions

Summary The problem of combining independent updates to a program is examined in the context of applicative programs. A partial semantic merge rule is given together with the conditions under which it is guaranteed to be correct, and the conditions under which a string merge corresponds to a semantic merge are examined. The theoretical work reported here contains initial steps towards a solution of the software merging problem and is not sufficient for producing a practical system.     

Enhanced-spectrum-based map merging for multi-robot systems

This paper addresses the problem of grid map merging for multi-robot systems, which can be resolved by acquiring the map transformation matrix (MTM) among robot maps. Without the initial correspondence or any rendezvous among robots, the only way to acquire the MTM is to find and match the common regions of individual robot maps. This paper proposes a novel map merging technique which is capable of merging individual robot maps by matching the spectral information of robot maps. The proposed technique extracts the spectra of robot maps and enhances the extracted spectra using visual landmarks. Then, the MTM is accurately acquired by finding the maximum cross-correlation among the enhanced spectra. Experimental results in outdoor environments show that the proposed technique was performed successfully. Also, the comparison result shows that the map merging errors were significantly reduced by the proposed technique.     

On judgment aggregation in abstract argumentation

Judgment aggregation is a field in which individuals are required to vote for or against a certain decision (the conclusion) while providing reasons for their choice. The reasons and the conclusion are logically connected propositions. The problem is how a collective judgment on logically interconnected propositions can be defined from individual judgments on the same propositions. It turns out that, despite the fact that the individuals are logically consistent, the aggregation of their judgments may lead to an inconsistent group outcome, where the reasons do not support the conclusion. However, in this paper we claim that collective irrationality should not be the only worry of judgment aggregation. For example, judgment aggregation would not reject a consistent combination of reasons and conclusion that no member voted for. In our view this may not be a desirable solution. This motivates our research about when a social outcome is ‘compatible’ with the individuals’ judgments. The key notion that we want to capture is that any individual member has to be able to defend the collective decision. This is guaranteed when the group outcome is compatible with its members views. Judgment aggregation problems are usually studied using classical propositional logic. However, for our analysis we use an argumentation approach to judgment aggregation problems. Indeed the question of how individual evaluations can be combined into a collective one can also be addressed in abstract argumentation. We introduce three aggregation operators that satisfy the condition above, and we offer two definitions of compatibility. Not only does our proposal satisfy a good number of standard judgment aggregation postulates, but it also avoids the problem of individual members of a group having to become committed to a group judgment that is in conflict with their own individual positions.     

On principle-based evaluation of extension-based argumentation semantics

The increasing variety of semantics proposed in the context of Dung's theory of argumentation makes more and more inadequate the example-based approach commonly adopted for evaluating and comparing different semantics. To fill this gap, this paper provides two main contributions. First, a set of general criteria for semantics evaluation is introduced by proposing a formal counterpart to several intuitive notions related to the concepts of maximality, defense, directionality, and skepticism. Then, the proposed criteria are applied in a systematic way to a representative set of argumentation semantics available in the literature, namely grounded, complete, preferred, stable, semi-stable, ideal, prudent, and CF2 semantics.     

Organizational and behavioural issues raised by intelligent argumentation systems

This paper introduces and reviews intelligent argumentation systems. It seeks to define what such systems are, and to emphasize the crucial distinction between argument represenation and argument generation programs. Such a review includes both working programs and design ideas. The paper also explores some domain applications, suggesting the wide-ranging motivations which have stimulated the creation of such systems, and suggesting a model of roles which such systems play, such as critic and tutor. These roles have hitherto been almost wholly for individual decision support, and so the paper suggests some ways in which current roles can be generalized from individual to group support. Finally a model is put forward for answering questions such as: Where in an organization would such group systems fit? What is so different about such systems from other support systems? How do such systems relate to newly emerging organizational structures?     

Computer-mediated communication: problems and potentials of argumentation support systems

Argumentation support systems have both advantages and disadvantages. For the individual, there is an increased power to express herself and to gain recognition and reward for the extra effort and frankness required, but at the cost of slowing down work, making the user constantly explain herself, and putting her statements at risk of being taken out of context. For the organisation, there is a gain in increased information sharing — the bane of current computer-mediated communication (CMC) systems — as the user is motivated to present relevant and convincing evidence to back up her statements, but at the cost of undermining ‘traditional' organisational structures and hierarchies.     

Fast and accurate map merging for multi-robot systems

We present a new algorithm for merging occupancy grid maps produced by multiple robots exploring the same environment. The algorithm produces a set of possible transformations needed to merge two maps, i.e translations and rotations. Each transformation is weighted, thus allowing to distinguish uncertain situations, and enabling to track multiple cases when ambiguities arise. Transformations are produced extracting some spectral information from the maps. The approach is deterministic, non-iterative, and fast. The algorithm has been tested on public available datasets, as well as on maps produced by two robots concurrently exploring both indoor and outdoor environments. Throughout the experimental validation stage the technique we propose consistently merged maps exhibiting very different characteristics.

Efficient datapath merging for the overhead reduction of run-time reconfigurable systems

High latencies in FPGA reconfiguration are known as a major overhead in run-time reconfigurable systems. This overhead can be reduced by merging multiple data flow graphs representing different kernels of the original program into a single (merged) datapath that will be configured less often compared to the separate datapaths scenario. However, the additional hardware introduced by this technique increases the kernels execution time. In this paper, we present a novel datapath merging technique that reduces both the configuration and execution times of kernels mapped on the reconfigurable fabric. Experimental results show up to 13% reduction in the configuration and execution times of kernels from media-bench workloads, compared to previous art on datapath merging. When compared to conventional high-level synthesis algorithms, our proposal reduces kernels configuration and execution times by up to 48%.     

Computer decision-support systems for public argumentation: assessing deliberative legitimacy

Recent proposals for computer-assisted argumentation have drawn on dialectical models of argumentation. When used to assist public policy planning, such systems also raise questions of political legitimacy. Drawing on deliberative democratic theory, we elaborate normative criteria for deliberative legitimacy and illustrate their use for assessing two argumentation systems. Full assessment of such systems requires experiments in which system designers draw on expertise from the social sciences and enter into the policy deliberation itself at the level of participants.

Practical reasoning as presumptive argumentation using action based alternating transition systems

In this paper we describe an approach to practical reasoning, reasoning about what it is best for a particular agent to do in a given situation, based on presumptive justifications of action through the instantiation of an argument scheme, which is then subject to examination through a series of critical questions. We identify three particular aspects of practical reasoning which distinguish it from theoretical reasoning. We next provide an argument scheme and an associated set of critical questions which is able to capture these features. In order that both the argument scheme and the critical questions can be given precise interpretations we use the semantic structure of an Action-Based Alternating Transition System as the basis for their definition. We then work through a detailed example to show how this approach to practical reasoning can be applied to a problem solving situation, and briefly describe some other previous applications of the general approach. In a second example we relate our account to the social laws paradigm for co-ordinating multi-agent systems. The contribution of the paper is to provide firm foundations for an approach to practical reasoning based on presumptive argument in terms of a well-known model for representing the effects of actions of a group of agents.     

On the resolution-based family of abstract argumentation semantics and its grounded instance

This paper introduces a novel parametric family of semantics for abstract argumentation called resolution-based and analyzes in particular the resolution-based version of the traditional grounded semantics, showing that it features the unique property of satisfying a set of general desirable properties recently introduced in the literature. Additionally, an investigation of its computational complexity properties reveals that resolution-based grounded semantics is satisfactory also from this perspective.