Ultima Ratio-a visual language for argumentation

In the third act of Shakespeare's Hamlet, the hero is unsure whether to kill Claudius-the assassin of Hamlet's father-or not. He argues that if he does kill him, Claudius who is praying at that very moment goes to heaven and if he does not kill him Hamlet's father is not revenged. A contradiction. Ultima Ratio aims at formalization and visualization of argumentation for agents. An agent is constituted by a set of arguments and assumptions. Facing a particular world, the agent's believes may be inconsistent triggering a rational monologue to deal with the situation. Formally, we define a framework for argumentation based on extended logic programming under well-founded semantics. The system serves as decision support and is capable of detecting and removing contradictions and deriving conclusions of the agent's arguments. To demonstrate the structure and dynamics of the agent's argumentation, we visualise the process as dynamic construction of proof trees. The paper includes screenshots of the logical engine and the visualisation unit as exhibited at the computer arts exhibition Ars Electronica 98.