A general semi-structured formalism for computational argumentation: Definition, properties, and examples of application

In the field of computational argumentation several formalisms featuring different levels of abstraction and focusing on different aspects of the argumentation process have been developed. Their combined use, necessary to achieve a comprehensive formal coverage of the argumentation phenomenon, gives rise to a nontrivial interplay between different abstraction levels, so that counterintuitive or undesirable outcomes may result from the combination of formalisms which appear to be well-behaved when considered in isolation. To address this problem we introduce a semi-structured formalism for argumentation, called LAF-ensembles, capturing a set of essential features of structured arguments and define a class of set based argumentation frameworks appropriate to support a semantic assessment of arguments for LAF-ensembles. It is shown that, under suitable assumptions, the combination of a LAF-ensemble and of an appropriate argumentation framework is guaranteed to produce justification outcomes satisfying a set of essential requirements. The generality and usefulness of the proposed approach are demonstrated by illustrating its ability to capture as instances and enhance two structured argumentation formalisms from the literature, namely Vreeswijk's abstract argument systems and Modgil and Prakken's ASPIC+. In particular, a revised version of the latter formalism, properly dealing with generic contrariness and solving significant technical limitations of ASPIC+, is proposed.