Abstract Dialectical Frameworks:Semantics, Discussion Games, and Variations

Argumentation is an essential part of our daily life both in our individual and our social activities. The extensive trajectory of research on argumentation from Aristotle to today's computational argumentation in artificial intelligence shows how far research in argumentation has come. Argumentation theory can shed light on the process of decision making, from modeling to evaluating a problem. Models of argumentation reflect how arguments relate to one another, and semantics of models of argumentation reflect how to use argumentation for making a decision under inconsistent, controversial, and incomplete information. In this thesis we consider abstract dialectical frameworks (ADFs for short), one of the powerful formalisms of argumentation. The semantics of ADFs are methods proposed to evaluate the acceptance of the arguments. We begin by focusing on the semantical evaluation of ADFs, presenting two novel semantics, namely the strongly admissible and semi-stable semantics. Next, we introduce the first discussion games for ADFs to provide an explanation of why an argument of interest is to be accepted according to a given semantics. Furthermore, we present subclasses of ADFs and we investigate how the restrictions that we consider influence the semantic evaluation of such ADFs. Next, we combine argumentation with decision theory in the context of ADFs in order to model expected utility problems. With this work, we hope that we have advanced the knowledge on the field of formal argumentation

A Labelling Framework for Probabilistic Argumentation

The combination of argumentation and probability paves the way to new accounts of qualitative and quantitative uncertainty, thereby offering new theoretical and applicative opportunities. Due to a variety of interests, probabilistic argumentation is approached in the literature with different frameworks, pertaining to structured and abstract argumentation, and with respect to diverse types of uncertainty, in particular the uncertainty on the credibility of the premises, the uncertainty about which arguments to consider, and the uncertainty on the acceptance status of arguments or statements. Towards a general framework for probabilistic argumentation, we investigate a labelling-oriented framework encompassing a basic setting for rule-based argumentation and its (semi-) abstract account, along with diverse types of uncertainty. Our framework provides a systematic treatment of various kinds of uncertainty and of their relationships and allows us to back or question assertions from the literature

On the Difference between Assumption-Based Argumentation and Abstract Argumentation

Acknowledgements The first author has been supported by the National Research Fund, Luxembourg (LAAMI project) and by the Engineering and Physical Sciences Research Council (EPSRC, UK), grant ref. EP/J012084/1 (SAsSy project). The second and third authors have been supported by CNPq (Universal 2012 - Proc. no. 473110/2012-1), CAPES (PROCAD 2009) and CNPq/CAPES (Casadinho/PROCAD 2011).Peer reviewedPostprin

Properties of ABA+ for Non-Monotonic Reasoning

We investigate properties of ABA+, a formalism that extends the well studied structured argumentation formalism Assumption-Based Argumentation (ABA) with a preference handling mechanism. In particular, we establish desirable properties that ABA+ semantics exhibit. These pave way to the satisfaction by ABA+ of some (arguably) desirable principles of preference handling in argumentation and nonmonotonic reasoning, as well as non-monotonic inference properties of ABA+ under various semantics.Comment: This is a revised version of the paper presented at the worksho

On the Difference between Assumption-Based Argumentation and Abstract Argumentation

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On the Relative Expressiveness of Argumentation Frameworks, Normal Logic Programs and Abstract Dialectical Frameworks

We analyse the expressiveness of the two-valued semantics of abstract argumentation frameworks, normal logic programs and abstract dialectical frameworks. By expressiveness we mean the ability to encode a desired set of two-valued interpretations over a given propositional signature using only atoms from that signature. While the computational complexity of the two-valued model existence problem for all these languages is (almost) the same, we show that the languages form a neat hierarchy with respect to their expressiveness.Comment: Proceedings of the 15th International Workshop on Non-Monotonic Reasoning (NMR 2014

Preferences and Unrestricted Rebut

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Reasoning by Cases in Structured Argumentation

We extend the $ASPIC^+$ framework for structured argumentation so as to allow applications of the reasoning by cases inference scheme for defeasible arguments. Given an argument with conclusion `$A$ or $B$', an argument based on $A$ with conclusion $C$, and an argument based on $B$ with conclusion $C$, we allow the construction of an argument with conclusion $C$. We show how our framework leads to different results than other approaches in non-monotonic logic for dealing with disjunctive information, such as disjunctive default theory or approaches based on the OR-rule (which allows to derive a defeasible rule `If ($A$ or $B$) then $C$', given two defeasible rules `If $A$ then $C$' and `If $B$ then $C$'). We raise new questions regarding the subtleties of reasoning defeasibly with disjunctive information, and show that its formalization is more intricate than one would presume.Comment: Proceedings of SAC/KRR 201