In argumentation theory, Dung’s abstract framework provides a unifying view of several alternative semantics based on the notion of extension. In this context, we propose a general recursive schema for argumentation semantics, based on decomposition along the strongly connected components of the argumentation framework. We introduce the fundamental notion of SCC-recursiveness and we show that all Dung’s admissibility-based semantics are SCC-recursive, and therefore a special case of our schema. On these grounds, we argue that the concept of SCC-recursiveness plays a fundamental role in the study and definition of argumentation semantics. In particular, the space of SCC-recursive semantics provides an ideal basis for the investigation of new proposals: starting from the analysis of several examples where Dung’s preferred semantics gives rise to questionable results, we introduce four novel SCC-recursive semantics, able to overcome the limitations of preferred semantics, while differing in other respects
The issue of representing attacks to attacks in argumentation is receiving an increasing attention as a useful conceptual modelling tool in several contexts. In this paper we present AFRA, a formalism encompassing unlimited recursive attacks within argumentation frameworks. AFRA satisfies the basic requirements of definition simplicity and rigorous compatibility with Dung's theory of argumentation. This paper provides a complete development of the AFRA formalism complemented by illustrative examples and a detailed comparison with other recursive attack formalizations
In the traditional definition of Dung’s abstract argumentation framework (AF), the notion of attack is understood as a relation between arguments, thus bounding attacks to start from and be directed to arguments. This paper introduces a generalized definition of abstract argumentation framework called AFRA (Argumentation Framework with Recursive Attacks), where an attack is allowed to be directed towards another attack. From a conceptual point of view, we claim that this generalization supports a straightforward representation of reasoning situations which are not easily accommodated within the traditional framework. From the technical side, we first investigate the extension to the generalized framework of the basic notions of conflict-free set, acceptable argument, admissible set and of Dung’s fundamental lemma. Then we propose a correspondence from the AFRA to the AF formalism, showing that it satisfies some basic desirable properties. Finally we analyze the relationships between AFRA and a similar extension of Dung’s abstract argumentation framework, called EAF+ and derived from the recently proposed formalism EAF
Causes of cognitive impairment after stroke are not yet clear because a large number of sociodemographic and clinical variables complicate the understanding of the phenomenon. We aim to evaluate sociodemographic and clinical predictors of cognitive level and depression in subjects with different lesion laterality. We assessed 153 right (n = 87) and left (n = 66) unilateral first-ever stroke patients within the first year of illness with the Structured Clinical Interview for DSM-IV-Patient Edition, the Hamilton Depression Rating Scale, the Hamilton Anxiety Rating Scale, the State Trait Anger Expression Inventory, the Barthel Index, and the Mini Mental State Examination (MMSE). Sociodemographic variables were also measured. Sixty-two (41 %) patients suffered from Major Depression (MDD), and 26 (17 %) suffered from Minor Depression (MIND). An univariate analysis of variance showed that MMSE scores were different throughout the groups of left and right stroke patients with MDD, MIND and without depression. Left stroke patients with MDD were more cognitively impaired than all the other groups. This result was valid after controlling for the effect of lesion location on cognitive level difference between the groups. A series of stepwise multiple regression analyses indicated that depression severity was a predictor of cognitive level and vice-versa in left hemispheric stroke patients only. Moreover, educational level in right hemispheric stroke patients and state-anger and number of regions affected in left hemispheric stroke patients were other predictors of cognitive level. The study confirms the hypothesis that predictors of cognitive level and depression severity are different in subjects with different laterality of lesion and that MDD is associated with cognitive impairment in left stroke patients.
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