Structured argumentation in a mediator for online dispute resolution

Online dispute resolution is becoming the main method when dealing with a conflict in e-commerce. A family of defeasible reasoning patterns is used to provide a useful link between dispute resolution agents and legal doctrines. The proposed argumentation framework combines defeasible logic with temporal reasoning and argumentation with level of certainty. The evaluation of arguments depends on the stage of the dispute: commencement, discovery, pre-trial, arbitration, according to current practice in law. By applying the open world assumption to the rules, the argumentative semantics of defeasible logic is enriched with three types of negated rules which offer symmetrical means of argumentation for both disputants. A corollary of this extension consists in defining a specialized type of undercutting defeater. The theory is illustrated with the help of a concrete business-to-client case in a prototype implemented system.