Sylvie Doutre

On Decision Problems Related to the Preferred Semantics for Argumentation Frameworks

Argumentation is a form of reasoning, in which two agents cooperate in order to establish the validity of a given argument; this argument could be used to deduce some conclusion of interest. In this article, we look at the credulous and the sceptical decision problems under Dung’s preferred semantics, that is, the problems of deciding if an argument belongs to one or to every preferred extension of an argumentation framework. We present two proof theories for the credulous decision problem and an algorithm which computes one of them. We show how these proof theories can be used for the sceptical decision problem in two particular cases of argumentation frameworks and we give an algorithm which answers that problem in the general case.

On Sceptical Versus Credulous Acceptance for Abstract Argument Systems

At a high level of abstraction, many systems of argumentation can be represented by a set of abstract arguments, and a binary relation between these abstract arguments describing how they contradict each other. Acceptable sets of arguments, called extensions, can be defined as sets of arguments that do not contradict one another, and attack all their attackers. We are interested in this paper in answering the question: is a given argument in all extensions of an argumentation system? In fact, what is likely to be useful in AI systems is not a simple yes/no answer, but some kind of well-argued answer, called a proof: if an argument is in every extension, why is it so? Several authors have described proofs that explain why a given argument is in at least one extension. In this paper, we show that a proof that an argument is in every extension can be a proof that some meta-argument is in at least one extension of a meta-argumentation system: this meta-argumentation system describes relationships between sets of arguments of the initial system.

Law-governed Linda as a semantics for agent dialogue protocols

Tuple spaces and the associated Linda language are a popular model for distributed computation, and Law-Governed Linda (LGL) is a variant allowing processes to have differential and secure access to tuple spaces. We propose a form of LGL as a means of implementing a multi-agent dialogue game protocol, such that utterances under the dialogue protocol are interpreted as actions on particular tuple spaces subject to certain laws. In this way, the tuple spaces, their associated law and the actions on them may be viewed as a semantics for the dialogue protocol syntax.

Dialectical Proofs for Constrained Argumentation

Constrained argumentation frameworks (CAF) generalize Dungs frameworks by allowing additional constraints on arguments to be taken into account in the definition of acceptability of arguments. These constraints are expressed by means of a logical formula which is added to Dungs framework. The resulting system captures several other extensions of Dungs original system. To determine if a set of arguments is credulously inferred from a CAF, the notion of dialectical proof (alternating pros and cons arguments) is extended for Dungs frameworks in order to respect the additional constraint. The new constrained dialectical proofs are computed by using Answer Set Programming.

A persuasion dialog for gaining access to information

This paper presents a formal protocol for agents engaged in argumentation over access to information sources. Obtaining relevant information is essential for agents engaged in autonomous, goal-directed behavior, but access to such information is usually controlled by other autonomous agents having their own goals. Because these various goals may be in conflict with one another, rational interactions between the two agents may take the form of a dialog, in which requests for information are successively issued, considered, justified and criticized. Even when the agents involved in such discussions agree on all the arguments for and the arguments against granting access to some information source, they may still disagree on their preferences between these arguments. To represent such situations, we design a protocol for dialogs between two autonomous agents for seeking and granting authorization to access some information source. This protocol is based on an argumentation dialog where agents handle specific preferences and acceptability over arguments. We show how this argumentation framework provides a semantics to the protocol dedicated to the exchange of arguments, and we illustrate the proposed framework with an example in medicine.

Determining preferences through argumentation

Arguments concerning what an agent should do cannot be considered in isolation: they occur in the context of debates where arguments attacking and defending each other are advanced. This is recognised by the use of argumentation frameworks which determine the status of an argument by reference to its presence in a coherent position: a subset of the arguments advanced which is collectively able to defend itself against all attackers. Where the position concerns practical reasoning, defence may be made by making a choice justified in terms of the values of an agent. Participants in the debate, however, are typically not neutral in their attitude towards the arguments: there will be arguments they wish to accept and others they wish to reject. In this paper we model how a participant in a debate can develop a position which is coherent both with respect to the attack relations between arguments and any value choices made. We define a framework for representing a set of arguments constituting the debate, and describe how a position including the desired arguments can be developed through a dialogue with an opponent. A key contribution is that the value choices are made as part of the argumentation process, and need not be determined in advance.

Encoding Argument Graphs in Logic

Argument graphs are a common way to model argumentative reasoning. For reasoning or computational purposes, such graphs may have to be encoded in a given logic. This paper aims at providing a systematic approach for this encoding. This approach relies upon a general, principle-based characterization of argumentation semantics.

Arguing for gaining access to information

This paper presents a protocol for agents engaged in argumentation over access to information sources. Obtaining relevant information is essential for agents engaged in autonomous, goal-directed behavior, but access to such information is usually controlled by other autonomous agents having their own goals. Because these various goals may be in conflict with one another, rational interactions between the two agents may take the form of a dialog, in which requests for information are successively issued, considered, justified and criticized. Even when the agents involved in such discussions agree on all the arguments for and the arguments against granting access to some information source, they may still disagree on their preferences between these arguments. To represent such situations, we design a protocol for dialogs between two autonomous agents for seeking and granting authorization to access some information source. This protocol is based on an argumentation dialog where agents handle specific preferences and acceptability over arguments.

Semantic Change and Extension Enforcement in Abstract Argumentation

Change in argumentation frameworks has been widely studied in the recent years. Most of the existing works on this topic are concerned with change of the structure of the argumentation graph (addition or removal of arguments and attacks), or change of the outcome of the framework (acceptance statuses of arguments). Change on the acceptability semantics that is used in the framework has not received much attention so far. Such a change can be motivated by different reasons, especially it is a way to change the outcome of the framework. In this paper, it is shown how semantic change can be used as a way to reach a goal about acceptance statuses in a situation of extension enforcement.

A Dynamic Logic Framework for Abstract Argumentation: Adding and Removing Arguments

A dynamic framework, based on the Dynamic Logic of Propositional Assignments (\(\mathsf {DL\text {-}PA}\)), has recently been proposed for Dung’s abstract argument system. This framework allows the addition and the removal of attacks, and the modification of the acceptance status of arguments. We here extend this framework in order to capture the addition and the removal of arguments. We then apply the framework on an access control case, where an agent engages in an argued dialogue to access some information controlled by another agent.