L. van der Torre

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.

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

Virtual Organizations as Normative Multiagent Systems

In this paper we propose a conceptual model of virtual organizations as normative multiagent systems. The dynamic aspects of virtual organizations are modeled using aspects of speech act theory and Searles theory of the construction of social reality. We illustrate the use of our model by discussing an example of distributed access control policies. We show how the model captures the distinction between local and global authorities, and between local and global norm enforcement policies.

Local policies for the control of virtual communities

Here we study the rational balance between local and global policies in Web based distributed systems. We use a logical framework for multiagent systems to model obligations and permissions composing policies. In particular, a qualitative decision theory allows agents to trade off the decision of respecting a norm against the consequences of not respecting it: the possibility that they are considered violators and thus sanctioned. Global policies refer not to the existence of a local norm but to the fact that it is enforced by the local authority by recognizing and sanctioning violations.

Programming Normative Artifacts with Declarative Obligations and Prohibitions

Abstract—Normative concepts (e.g., obligations and prohibitions) are seen as a suitable tool for regulating the observable behavior of software agents. An enforcement mechanism – a process that detects when a norm is active, detects violations of the norms and handles these violations – is crucial for the practical use of norms in the construction of multi-agent systems. We propose a programming language for programming normative artifacts in terms of “declarative” norms referring to a state of the world (as opposed to “procedural” norms only referring to actions), and introduce the operational semantics of the norm enforcement mechanism.

Fulfilling or violating obligations in normative multiagent systems

A theory of rational decision making in normative multi-agent systems has to distinguish among the many reasons why agents fulfill or violate obligations. We propose a classification of such reasons for single cognitive agent decision making in a single normative system, based on the increasing complexity of this agent. In the first class we only consider the agents motivations, in the second class we consider also its abilities, in the third class we consider also its beliefs, and finally we consider also sensing actions to observe the environment. We sketch how the reasons can be formalized in a normative multiagent system with increasingly complex cognitive agents.

Power and dependence relations in groups of agents

We present a formal model of multiagent systems to analyze the relations of power and dependence underlying group behaviors such as cooperation. Inspired by the work of Castelfranchi we define these relations by means of a description of goals and skills of single agents. We show how our framework can be used to describe social and organizational structures as emergent properties of a collection of individuals.

Admissible agreements among goal-directed agents

We study admissible coalitions in goal-directed multiagent systems. We define a qualitative criterion of admissibility in which a coalition has itself all the necessary information to check admissibility. We show also that, under some assumptions on preference relations of the agents, this admissibility criterion can be used to reduce the search space in a game theoretical approach.