ABAplus: Attack Reversal in Abstract and Structured Argumentation with Preferences

We present ABAplus, a system that implements reasoning with the argumentation formalism ABA+. ABA+ is a structured argumentation formalism that extends Assumption-Based Argumentation (ABA) with preferences and accounts for preferences via attack reversal. ABA+ also admits as instance Preference-based Argumentation which accounts for preferences by reversing attacks in abstract argumentation (AA). ABAplus readily implements attack reversal in both AA and ABAstyle structured argumentation. ABAplus affords computation, visualisation and comparison of extensions under five argumentation semantics. It is available both as a stand-alone system and as a web application

Declarative Algorithms and Complexity Results for Assumption-Based Argumentation

Peer reviewe

Reasoning over Assumption-Based Argumentation Frameworks via Answer Set Programming

Formal argumentation is a vibrant research area within artificial intelligence, in particular in knowledge representation and reasoning. Computational models of argumentation are divided into abstract and structured formalisms. Since its introduction in 1995, abstract argumentation, where the structure of arguments is abstracted away, has been much studied and applied. Structured argumentation formalisms, on the other hand, contain the explicit derivation of arguments. This is motivated by the importance of the construction of arguments in the application of argumentation formalisms, but also makes structured formalisms conceptually and often computationally more complex than abstract argumentation. The focus of this work is on assumption-based argumentation (ABA), a major structured formalism. Specifically we address the relative lack of efficient computational tools for reasoning in ABA compared to abstract argumentation. The computational efficiency of ABA reasoning systems has been markedly lower than the systems for abstract argumentation. In this thesis we introduce a declarative approach to reasoning in ABA via answer set programming (ASP), drawing inspiration from existing tools for abstract argumentation. In addition, we consider ABA+, a generalization of ABA that incorporates preferences into the formalism. The complexity of reasoning in ABA+ is higher than in ABA for most problems. We are able to extend our declarative approach to some ABA+ reasoning problems. We show empirically that our approach vastly outperforms previous reasoning systems for ABA and ABA+

Labellings for assumption-based and abstract argumentation

The semantics of Assumption-Based Argumentation (ABA) frameworks are traditionally characterised as assumption extensions, i.e. sets of accepted assumptions. Assumption labellings are an alternative way to express the semantics of flat ABA frameworks, where one of the labels in, out, or undec is assigned to each assumption. They are beneficial for applications where it is important to distinguish not only between accepted and non-accepted assumptions, but further divide the non-accepted assumptions into those which are clearly rejected and those which are neither accepted nor rejected and thus undecided. We prove one-to-one correspondences between assumption labellings and extensions for the admissible, grounded, complete, preferred, ideal, semi-stable and stable semantics. We also show how the definition of assumption labellings for flat ABA frameworks can be extended to assumption labellings for any (flat and non-flat) ABA framework, enabling reasoning with a wider range of scenarios. Since flat ABA frameworks are structured instances of Abstract Argumentation (AA) frameworks, we furthermore investigate the relation between assumption labellings for flat ABA frameworks and argument labellings for AA frameworks. Building upon prior work on complete assumption and argument labellings, we prove one-to-one correspondences between grounded, preferred, ideal, and stable assumption and argument labellings, and a one-to-many correspondence between admissible assumption and argument labellings. Inspired by the notion of admissible assumption labellings we introduce committed admissible argument labellings for AA frameworks, which correspond more closely to admissible assumption labellings of ABA frameworks than admissible argument labellings do