Approximating stability for applied argument-based inquiry

Abstract

• Detecting stability is a CoNP-complete problem in dynamic argumentation. • A claim is stable if more information cannot change its justification status. • We propose a sound and polynomial approximation algorithm for estimating stability. • We provide empirical and theoretical analyses of the algorithm’s performance. • The algorithm is applied in three use cases at the Netherlands Police. In argument-based inquiry, agents jointly construct arguments supporting or attacking a topic claim to find out if the claim can be accepted given the agents’ knowledge bases. While such inquiry systems can be used for various forms of automated information intake, several efficiency issues have so far prevented widespread application. In this paper, we aim to tackle these efficiency issues by exploring the notion of stability: can additional information change the justification status of the claim under discussion? Detecting stability is not tractable for every input, since the problem is CoNP-complete, yet in practical applications it is essential to guarantee efficient computation. This makes approximation a viable alternative. We present a sound approximation algorithm that recognises stability for many inputs in polynomial time and discuss several of its properties. In particular, we show that the algorithm is sound and identify constraints on the input under which it is complete. As a final contribution of this paper, we describe how the proposed algorithm is used in three different case studies at the Netherlands Police.