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Christian Strasser

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4 papers

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KR Conference 2025 Conference Paper

Compactness and Preservation in Logical Argumentation Frameworks

Ofer Arieli
Christian Strasser

Logic-based argumentation is a formal method for constructing, evaluating and comparing arguments. In this paper we address two (related) key issues concerning the representation of logical argumentation frameworks: how to describe them in a compact way, and how to move from one framework to another while preserving their basic logical characteristics. The results are applied to various forms of attack rules and different kinds of argumentative semantics, and are demonstrated for transitions between several 3-valued logics and classical logic. As a byproduct, our results are also used for converting logic-based argumentation frameworks to assumption-based argumentation frameworks.

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KR Conference 2024 Conference Paper

Deontic Reasoning Based on Inconsistency Measures

Ofer Arieli
Kees van Berkel
Badran Raddaoui
Christian Strasser

Conflicts are inherent to normative systems. In this paper, we explore a novel approach to normative reasoning by quantifying the amount of conflicts within normative systems. We refine the idea from classical logic, according to which a formula is a consequence of a knowledge base in case its negation renders the knowledge base inconsistent. In our approach, whether a formula is a logical consequence depends, for instance, on its negation's marginal contribution to the inconsistency of the given knowledge base. Accordingly, various inconsistency measures and corresponding (nonmonotonic and paraconsistent) normative entailment relations are analyzed relative to a number of logical properties. To illustrate our approach, we adopt Input/Output logic, a renowned formalism in deontic logic, specifically designed for defeasible normative reasoning. As an application, the resulting entailment relations provide recommendations to agents for minimizing norm conflicts, and may be incorporated in a number of implementations (like the Tweety libraries and the LogiKey framework) by involving inconsistency measurements in normative reasoning.

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JAIR Journal 2024 Journal Article

The Goal after Tomorrow: Offline Goal Reasoning with Norms

Pere Pardo
Christian Strasser

Recent studies have focused on autonomous agents that select their own goals and then select actions to achieve these goals, using online Goal Reasoning (GR). GR agents can revise goals and plans at execution time if unexpected outcomes occur. However, for ethical or legal agent design, even the partial execution of an online plan may result in foreseeable norm violations. To prevent these violations, it is crucial to incorporate GR already at the planning phase. To this end, we design an offline GR system that can harbour normative systems or deontic logics for goal generation. Our main results include a characterization and comparison of the completeness classes for a variety of offline GR planners, and a discussion of the irreducibility of offline GR to pure planning methods.

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KR Conference 2016 Short Paper

Argumentative Approaches to Reasoning with Maximal Consistency

Ofer Arieli
Christian Strasser

Sequent-Based Argumentation Reasoning with the maximally consistent subsets (MCS) of the premises is a well-known approach for handling contradictory information. We introduce two argumentation-based methods for doing so: a declarative approach that is related to Dung-style semantics for abstract argumentation, and a computational approach that is based on extensions of Gentzentype proofs systems. This brings about a new perspective on reasoning with MCS which shows a strong link between the latter and argumentation systems, and which can be extended to related formalisms. A by-product of this is the introduction of a dynamic proof system for classical logic and rebuttal attacks, which is sound and complete with respect to Dung’s stable semantics for the associated argumentation framework. According to Dung (1995), abstract argumentation frameworks may be viewed as directed graphs as follows: Deﬁnition 1 An (abstract) argumentation framework is a pair AF = Args, Attack , where Args is a denumerable set of elements, called arguments, and Attack is a relation on Args ×Args, whose instances are called attacks. D A B C E Figure 1: An argumentation framework with ﬁve arguments and six attacks.