Collective Attacks in Assumption-Based Argumentation

Conflicts in argumentation-based frameworks are usually described in terms of attacks of arguments, or sets of arguments, on specific counter-arguments. In this paper we consider (assumption-based) argumentation frameworks, in which attacks have a more general form: they are performed on a collective of arguments that cannot stand together with the attacking arguments. We show that not only that this generalized form of attacks increases the expressive power of the argumentation frameworks, but in certain cases it also allows more sensible patterns of reasoning with conflicting considerations. Along the way, we also provide a novel characterization of the grounded semantics in prioritized argumentation frameworks.