Practical reasoning (PR), which is concerned with the generic question of what to do, is generally seen as a two steps process: (1) deliberation, in which an agent decides what state of affairs it wants to reach that is, its desires; and (2) means-ends reasoning, in which the agent looks for plans for achieving these desires. The agent's intentions are a consistent set of desires that are achievable together.This paper proposes the first argumentation system for PR that computes in one step the possible intentions of an agent, avoiding thus the drawbacks of the existing systems. The proposed system is grounded on a recent work on constrained argumentation systems, and satisfies the rationality postulates identified in argumentation literature, namely the consistency and the completeness of the results. (C) 2011 Elsevier Inc. All rights reserved.

This paper studies how to encode the problem of computing the extensions of an argumentation framework (under a given semantics) as a constraint satisfaction problem (CSP). Such encoding is of great importance since it makes it possible to use the very efficient solvers (developed by the CSP community) for computing the extensions. We focus on three families of frameworks: Dung's abstract framework, its constrained version and preference-based argumentation frameworks.

Constrained argumentation frameworks (CAF) generalize Dung's 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 Dung's framework. The resulting system captures several other extensions of Dung's 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 Dung's frameworks in order to respect the additional constraint. The new constrained dialectical proofs are computed by using Answer Set Programming.

We consider argumentation systems with several attack relations of different strength. We focus on the impact of various strength attacks on the semantics of such systems. First, we refine the classical notion of defence, by comparing the strength of an attack with the strength of a counter-attack. Then, we propose different ways to compare defenders, and sets of defenders. That enables us to define admissible sets offering a best defence for their elements.

There already exist some links between argumentation and game theory. For instance, dynamic games can be used for simulating interactions between agents in an argumentation process. In this paper, we establish a new link between these domains in a static framework: we show how an argumentation framework can be translated into a CP-Boolean game and how this translation can be used for computing extensions of argumentation semantics. We give formal algorithms to do so.

We present two prudent semantics within Dung's theory of argumentation. They are based on two new notions of extension, referred to as p-extension and c-extension. Two arguments cannot belong to the same p-extension whenever one of them attacks indirectly the other one. Two arguments cannot belong to the same c-extension whenever one of them indirectly attacks a third argument while the other one indirectly defends the third. We argue that our semantics lead to a better handling of controversial arguments than Dung's ones. We compare the prudent inference relations induced by our semantics w.r.t. cautiousness; we also compare them with the inference relations induced by Dung's semantics.

Practical reasoning (PR), which is concerned with the generic question of what to do, is generally seen as a two steps process: (1) deliberation, in which an agent decides what state of affairs it wants to reach –that is, its desires; and (2) means-ends reasoning, in which the agent looks for plans for achieving these desires. A desire is justified if it holds in the current state of the world, and feasible if there is a plan for achieving it. The agent’s intentions are thus a consistent subset of desires that are both justified and feasible. This paper proposes the first argumentation system for PR that computes in one step the intentions of an agent, allowing thus to avoid the drawbacks of the existing systems. The proposed system is grounded on a recent work on constrained argumentation systems, and satisfies the rationality postulates identified in argumentation literature, namely the consistency and the completeness of the results.

In Dung’s argumentation system, acceptable sets of arguments are de- fined as sets of arguments that attack all their attackers, and that do not contain any direct contradiction. However, in many applications, the presence of indirect contradictions should prevent a set from being acceptable. The family of prudent semantics has been proposed as an answer to this problem. We are interested in this paper in determining whether a given set of arguments is included in at least one acceptable set under the prudent preferred semantics. To this end, we propose a dialectical framework and several proof theories.

In this paper, the problem of deriving sensible information from a collection of argumentation systems coming from different agents is addressed. The underlying argumentation theory is Dung's one: each argumentation system gives both a set of arguments and the way they interact (i.e., attack or non-attack) according to the corresponding agent. The inadequacy of the simple, yet appealing, method which consists in voting on the agents' selected extensions calls for a new approach. To this purpose, a general framework for merging argumentation systems from Dung's theory of argumentation is presented. The objective is achieved through a three-step process: first, each argumentation system is expanded into a partial system over the set of all arguments considered by the group of agents (reflecting that some agents may easily ignore arguments pointed out by other agents, as well as how such arguments interact with her own ones); then, merging is used on the expanded systems as a way to solve the possible conflicts between them, and a set of argumentation systems which are as close as possible to the whole profile is generated; finally, voting is used on the selected extensions of the resulting systems so as to characterize the acceptable arguments at the group level.

We consider bipolar argumentation frameworks, which extend Dung's argumentation frameworks by handling two independent kinds of interaction between arguments, attack and support. In this bipolar context, we propose new semantics for coping with the problem of controversial arguments (arguments which indirectly attack and indirectly defend a same argument).

We present a generalization of Dung's theory of argumentation enabling to take account for some additional constraints on the admissible sets of arguments, expressed as a propositional formula over the set of arguments. We point out several semantics for such constrained argumentation frameworks, and compare the corresponding inference relations w.r.t. cautiousness. We show that our setting encompasses some previous approaches based on Dung's theory as specific cases. We also investigate the complexity issue for the inference relations in the extended setting. Interestingly, we show that our generalization does not lead to a complexity shift w.r.t. inference for several semantics.

In this paper, we address the problem of deriving sensible information from a collection of argumentation systems coming from different agents. A general framework for merging argumentation systems from Dung's theory of argumentation is presented. Each argumentation system gives both a set of arguments and the way they interact (i.e. attack or non-attack) according to the corresponding agent. The aim is to define the argument system (or the set of argument systems) that best represents the group. Our framework is general enough to handle the case when agents do not share the same set of arguments. Merging argumentation systems is shown as a valuable approach for defining (sets of) arguments acceptable by the group.

We present new careful semantics within Dung’s theory of argumentation. Under such careful semantics, two arguments cannot belong to the same extension whenever one of them indirectly attacks a third argument while the other one indirectly defends the third. We argue that our semantics lead to a better handling of controversial arguments than Dung’s ones in some settings. We compare the careful inference relations induced by our semantics w.r.t. cautiousness; we also compare them with the inference relations induced by Dung’s semantics.

This paper is centered on the family of Dung's finite argumentation frameworks when the attacks relation is symmetric (and nonempty and irreflexive). We show that while this family does not contain any well-founded framework, every element of it is both coherent and relatively grounded. Then we focus on the acceptability problems for the various semantics introduced by Dung, yet generalized to sets of arguments. We show that only two distinct forms of acceptability are possible when the considered frameworks are symmetric. Those forms of acceptability are quite simple, but tractable; this contrasts with the general case for which all the forms of acceptability are intractable (except for the ones based on grounded or naive extensions).

We present new prudent semantics within Dung's theory of argumentation. Under such prudent semantics, two arguments cannot belong to the same extension whenever one of them attacks indirectly the other one. We argue that our semantics lead to a better handling of controversial arguments than Dung's ones. We compare the prudent inference relations induced by our semantics w.r.t. cautiousness; we also compare them with the inference relations induced by Dung's semantics.