Revising option status in argument-based decision systems1

Decision making is usually based on the comparative evaluation of different op-tions by means of a decision criterion. Recently, the qualitative pessimistic criterionwas articulated in terms of a four-step argumentation process: i) to build argumentsin favor/against each option, ii) to compare and evaluate those arguments, iii) toassign a status for each option, and iv) to rank-order the options on the basis oftheir status. Thus, the argumentative counter-part of the pessimistic criterion pro-vides not only the “best” option to the user but also the reasons justifying thisrecommendation. The aim of this paper is to study the dynamics of this argumentation model. Theidea is to study how the ordering on options changes in light of a new argument. Forthis purpose, we study under which conditions an option may change its status, andunder which conditions the new argument has no impact on the status of options,and consequently, on the ordering. This amounts to study how the acceptability ofarguments evolves when the decision system is extended by new arguments. In the paper, we focus on two acceptability semantics: the skeptical grounded semantics,and the credulous preferred semantics.