Guido Boella

Normative framework for normative system change

The paper proposes a complex adaptive systems approach to the formation of an ontology and a shared lexicon in a group of distributed agents with only local interactions and no central control authority. The underlying mechanisms are explained in some detail and results of some experiments with robotic agents are briefly reported.Normative systems in a multiagent system must be able to evolve over time, for example due to actions creating or removing norms in the system. The only formal framework to evaluate and classify normative system change methods is the so-called AGM framework of theory change, which has originally been developed as a framework to describe and classify both belief and normative system change. However, it has been used for belief change only, since the beliefs or norms are represented as propositional formulas. We therefore propose, as a normative framework for normative system change, to replace propositional formulas in the AGM framework of theory change by pairs of propositional formulas, representing the rule based character of norms, and to add several principles from the input/output logic framework. In this new framework, we show that some of the AGM properties cannot be expressed, and other properties are consistent only for some logics, but not for others.

Introduction to normative multiagent systems

This article introduces the research issues related to and definition of normative multiagent systems. It also describes the papers selected from NorMAS05 that are part of this double special issue and relates the papers to each other.

Permissions and obligations in hierarchical normative systems

In this paper we discuss different types of permissions and their roles in deontic logic. We study the distinction between weak and strong permissions in the context of input/output logic, combining the logic with constraints, priorities and hierarchies of normative authorities. In this setting we observe that the notion of prohibition immunity no longer applies, and we introduce a new notion of permission as exception and a new distinction between static and dynamic norms. We show that strong permissions can dynamically change a normative system by adding exceptions to obligations, provide an explicit representation of what is permitted to the subjects of the normative system and allow higher level authorities to limit the changes that lower level authorities can do to the normative system.

Attributing mental attitudes to normative systems

The role of norms in the formalization of multiagent sys-tems is to stabilize the behavior of a multiagent system,and thus they play the same role for such systems as in-tentions do for single agent systems. However, it is still anopen problem whether they should be represented explicitly,for example in a deontic logic, or they can also be repre-sented implicitly. Boella and Lesmo [1] propose a definitionof obligation in terms of beliefs, goals and desires, inspiredby Goffman’s game-theoretic interpretation of norms and byrecursive modelling. The aim of this definition is to distin-guish various reasons why agents fulfil or violate obligations.In this paper, we extend [1]’s definition of sanction basednorms by explicitly attributing beliefs, desires and goalsboth to the bearer of a norm and to the normative system.Boella and Lesmo [1] propose to attribute mental statesto normative systems such as legal or moral systems, as aninstance of Dennett’s

Dynamics in Argumentation with Single Extensions: Abstraction Principles and the Grounded Extension

In this paper we consider the dynamics of abstract argumentation in Baroni and Giacomins framework for the evaluation of extension based argumentation semantics. Following Baroni and Giacomin, we do not consider individual approaches, but we define general principles or postulates that individual approaches may satisfy. In particular, we define abstraction principles for the attack relation, and for the arguments in the framework. We illustrate the principles on the grounded extension. In this paper we consider only principles for the single extension case, and leave the multiple extension case to further research.

A game theoretic approach to contracts in multiagent systems

Contracts are used to create new interaction possibilities among agents, and therefore play an important role in the game theoretic analysis of agent interaction. We use normative multiagent systems to model both the contracts and the interactions. In particular, we formalize contracts as systems of regulative and constitutive norms within a larger rule-governed setting and, using recursive modeling, we develop a game theory wherein agents make contracts. We show how agents can modify the behavior of normative systems by means of constitutive rules in the contract changing these systems, and we illustrate how agents use the game theory within contract negotiation in organizations

Norm governed multiagent systems: the delegation of control to autonomous agents

When agents make decisions, they have to deal with norms regulating the system. In this paper we therefore propose a rule-based qualitative decision and game theory combining ideas from multiagent systems and normative systems. Whereas normative systems are typically modelled as a single authority that imposes obligations and permissions on the agents, our theory is based on a multiagent structure of the normative system. We distinguish between agents whose behavior is governed by norms, so-called defender agents who have the duty to monitor violations of these norms and apply sanctions, and autonomous normative systems that issue norms and watch over the behavior of defender agents. We show that autonomous normative systems can delegate monitoring and sanctioning of violations to defender agents, when bearers of obligations model defender agents, which in turn model autonomous normative systems.

Support in Abstract Argumentation

In this paper, we consider two drawbacks of Cayrol and Lagasque-Schiexs meta-argumentation theory to model bipolar argumentation frameworks. We consider first the “lost of admissibility” in Dungs sense and second, the definition of notions of attack in the context of a support relation. We show how to prevent these drawbacks by introducing support meta-arguments. Like the model of Cayrol and Lagasque-Schiex, our formalization confirms the use of meta-argumentation to reuse Dungs properties. We do not take a stance towards the usefulness of a support relation among arguments, though we show that if one would like to introduce them, it can be done without extending Dungs theory. Finally, we show how to use meta-argumentation to instantiate an argumentation framework to represent defeasible support. In this model of support, the support relation itself can be attacked.

The ontological properties of social roles in multi-agent systems: definitional dependence, powers and roles playing roles

In this paper we address the problem of defining social roles in multi-agent systems. Social roles provide the basic structure of social institutions and organizations. We start from the properties attributed to roles both in the multi-agent systems and the Object Oriented community, and we use them in an ontological analysis of the notion of social role. We identify three main properties of social roles. First, they are definitionally dependent on the institution they belong to, i.e. the definition of a role is given inside the definition of the institution. Second, they attribute powers to the agents playing them, like creating commitments for the institutions and the other roles. Third, they allow roles to play roles, in the same way as agents do. Using Input/Output logics, we propose a formalization of roles in multi-agent systems satisfying the three properties we identified.

Security policies for sharing knowledge in virtual communities

Knowledge management exploits the new opportunities of sharing knowledge among members of virtual communities in distributed computer networks, and knowledge-management systems are therefore modeled and designed as multiagent systems. In this paper, normative multiagent systems for secure knowledge management based on access-control policies are studied. It is shown how distributed access control is realized by means of local policies of access-control systems for documents of knowledge providers, and by means of global community policies regulating these local policies. Moreover, it is shown how such a virtual community of multiple knowledge providers respects the autonomy of the knowledge providers