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Probabilistic argumentation frameworks

In this paper, we extend Dungs seminal argument framework to form a probabilistic argument framework by associating probabilities with arguments and defeats. We then compute the likelihood of some set of arguments appearing within an arbitrary argument framework induced from this probabilistic framework. We show that the complexity of computing this likelihood precisely is exponential in the number of arguments and defeats, and thus describe an approximate approach to computing these likelihoods based on Monte-Carlo simulation. Evaluating the latter approach against the exact approach shows significant computational savings. Our probabilistic argument framework is applicable to a number of real world problems; we show its utility by applying it to the problem of coalition formation.

Towards a Formalisation of Electronic Contracting Environments

Clauses within contracts may be thought of as norms, specifying permissions, obligations and prohibitions on contract parties. In this paper, we present a formal representation of contracts, focusing on the specification of a model of norms. With this model, a norm is associated with a status, which may change as the environment, and the status of other norms, changes. We define a normative environment, which may be used to track the status of a set of norms throughout their lifecycle, and then describe a predicates that may be used to evaluate a norms status. Agents are able to use these predicates to reason about the status of norms, and how their actions will affect the normative environment. Finally, we show the applicability of our framework to real world domains by monitoring the execution of a contract taken from a real world scenario.

Subjective logic and arguing with evidence

This paper introduces a subjective logic based argumentation framework primarily targeted at evidential reasoning. The framework explicitly caters for argument schemes, accrual of arguments, and burden of proof; these concepts appear in many types of argument, and are particularly useful in dialogues revolving around evidential reasoning. The concept of a sensor is also useful in this domain, representing a source of evidence, and is incorporated in our framework. We show how the framework copes with a number of problems that existing frameworks have difficulty dealing with, and how it can be situated within a simple dialogue game. Finally, we examine reasoning machinery that enables an agent to decide what argument to advance with the goal of maximising its utility at the end of a dialogue.

Summary Report of The First International Competition on Computational Models of Argumentation

We review the First International Competition on Computational Models of Argumentation (ICMMA’15). The competition evaluated submitted solvers performance on four different computational tasks related to solving abstract argumentation frameworks. Each task evaluated solvers in ways that pushed the edge of existing performance by introducing new challenges. Despite being the first competition in this area, the high number of competitors entered, and differences in results, suggest that the competition will help shape the landscape of ongoing developments in argumentation theory solvers.

Formal arguments, preferences, and natural language interfaces to humans: an empirical evaluation

It has been claimed that computational models of argumentation provide support for complex decision making activities in part due to the close alignment between their semantics and human intuition. In this paper we assess this claim by means of an experiment: peoples evaluation of formal arguments — presented in plain English — is compared to the conclusions obtained from argumentation semantics. Our results show a correspondence between the acceptability of arguments by human subjects and the justification status prescribed by the formal theory in the majority of the cases. However, post-hoc analyses show that there are some significant deviations, which appear to arise from implicit knowledge regarding the domains in which evaluation took place. We argue that in order to create argumentation systems, designers must take implicit domain specific knowledge into account.

Arguing using opponent models

While researchers have looked at many aspects of argumentation, an area often neglected is that of argumentation strategies. That is, given multiple possible arguments that an agent can put forth, which should be selected in what circumstances. In this paper we propose a heuristic that implements one such strategy. The heuristic is built around opponent modelling, and operates by selecting the line of argument that yields maximal utility, based on the opponents expected response, as computed by the opponent model. An opponent model may be recursive, with the opponent modelling of the agent captured by the original agents opponent model. Computing the utility for each possible line of argument is thus done using a variant of M* search, which in itself is an enhancement of min-max search. After describing the M* algorithm we show how it may be adapted to the argumentation domain, and then study what enhancements are possible for more specific types of dialogue. Finally, we discuss how this heuristic may be extended in future work, and its relevance to argumentation theory in general.

Moving Between Argumentation Frameworks

Abstract argument frameworks have been used for various applications within multi-agent systems, including reasoning and negotiation. Different argument frameworks make use of different inter-argument relations and semantics to identify some subset of arguments as coherent, yet there is no easy way to map between these frameworks; most commonly, this is done manually according to human intuition. In response, in this paper, we show how a set of arguments described using Dungs or Nielsens argument frameworks can be mapped from and to an argument framework that includes both attack and support relations. This mapping preserves the frameworks semantics in the sense that an argument deemed coherent in one framework is coherent in the other under a related semantics. Interestingly, this translation is not unique, with one set of arguments in the support based framework mapping to multiple argument sets within the attack only framework. Additionally, we show how EAF can be mapped into a subset of the argument interchange format (AIF). By using this mapping, any other argument framework using this subset of AIF can be translated into a DAF while preserving its semantics.

Towards a Monitoring Framework for Agent-Based Contract Systems

The behaviours of autonomous agents may deviate from those deemed to be for the good of the societal systems of which they are a part. Norms have therefore been proposed as a means to regulate agent behaviours in open and dynamic systems, and may be encoded in electronic contracts in order to specify the obliged, permitted and prohibited behaviours of agents that are signatories to such contracts. Enactment and management of electronic contracts thus enables the use of regulatory mechanisms to ensure that agent behaviours comply with the encoded norms. To facilitate such mechanisms requires monitoring in order to detect and explain violation of norms. In this paper we propose a framework for monitoring that is to be implemented and integrated into a suite of contract enactment and management tools. The framework adopts a non-intrusive approach to monitoring, whereby the states of a contract with respect to its contained norms can be inferred on the basis of messages exchanged. Specifically, the framework deploys agents that observe messages sent between contract signatories, where these messages correspond to agent behaviours and therefore indicate whether norms are, or are in danger of, being violated.

Preferences and unrestricted rebut

The work of Caminada & Amgoud presents two possible ways of satisfying the rationality postulates: one using restricted rebut, and one using unrestricted rebut. Subsequent work on ASPIC+ has extended the work of Caminada & Amgoud, for instance by allowing preferences over arguments. However, such extensions have utilised restricted rebut only. In the current paper, we make the case for unrestricted rebut, and provide a formalism (called ASPIC−) that implements preferences between the defeasible rules, in the context of unrestricted rebut while still satisfying the rationality postulates of Caminada & Amgoud

Revisiting Support in Abstract Argumentation Systems

Dungs original argumentation frameworks have been extended in various ways. One such extension introduces positive interactions, or support, between arguments. Frameworks containing evidential, necessary, and deductive supports have been proposed, and it is natural to compare these and analyse whether translations between these are possible. Although a positive answer was given in the necessary and deductive cases, it was claimed that evidential support cannot be expressed by any other type and that it cannot be handled together with them in a single framework. In this paper we show that it is not the case and that there exists a natural translation between argumentation frameworks with necessities and evidential argumentation systems.