Groups as Agents with Mental Attitudes Guido Boella Dipartimento di Informatica Universit` a di Torino - Italy e-mail: guido@di.unito.it Leendert van der Torre CWI Amsterdam - The Netherlands e-mail: torre@cwi.nl Abstract We discuss a model of cooperation among autonomous agents, based on the attribution of mental attitudes to groups: these attitudes represent the shared beliefs and ob- jectives and the wish to reduce the costs for the mem- bers. When agents take a decision they have to recursively model what their partners are expected to do under the as- sumption that they are cooperative, and they have to adopt the goals and desires attributed to the group: other- wise, they are considered by the other members uncoopera- tive and thus liable. 1. Introduction In multiagent systems, autonomous agents interact with each other, they play roles in organizations [14], they are hold responsible for some task and they are subject to obli- gations and permissions [19]. According, e.g., to [11, 14] and [26], a multiagent system should make minimal com- mitments on the structure of its heterogeneous members, e.g., that their autonomous behavior is driven by the repre- sentation of mental attitudes like beliefs, desires, goals or intentions. At the same time, in a multiagent system, agents form coalitions and groups to achieve goals which they are not able to pursue individually. A group in a multiagent sys- tem interacts as a whole with other agents, it plays roles in organizations, it is hold responsible for some task and it is subject to obligations and permissions [22]. But if groups act as agents in the multiagent system, groups should be described in the same terms as agents: they should be at- tributed mental attitudes like beliefs, desires, goals or inten- tions and autonomous behavior. In this paper, starting from Boella et al. [1]’s model of cooperation, we address the following research questions: • How can groups be considered as agents and how can they be attributed beliefs, desires and goals? • Which properties of cooperation can be shown in such a definition of a group? Boella et al. [1] argue that the basic elements of a gen- eral model of cooperation among the members of a group of autonomous agents are: 1) considering the overall ad- vantage that the group gains from the decisions of the sin- gle agents by means of a shared utility function; 2) adopt- ing the goals of the partners, if their achievement increases the advantage for the group. These elements must be com- bined with the ability of social agents to model in a recur- sive way ([16]) the decisions of the other partners, so to pre- dict their behavior. Boella et al. [1] show that, if these ele- ments are present, the group’s behavior satisfies the basic properties of cooperation required by Cohen and Levesque [10], Grosz and Kraus [18], Tambe [27] and Yen et al. [30], like helpful behavior, communication, conflict avoidance, et cetera. Boella et al. [1]’s approach, however, suffers from the lack of a precise model of beliefs, desires and goals and from the dichotomy between these qualitative notions and the quantitative approach of the decision theory they use. In this paper, we propose a model of cooperation which provide a precise formalization of the notions of belief, de- sire and goal of the agents, using a logical framework; sec- ond, instead of using classical decision theory, we base the deliberation process of agents on a qualitative decision the- ory inspired to the BOID architecture of Broersen et al. [7]. The methodology we adopt is the same as the logical mul- tiagent framework we used for normative multiagent sys- tems [2, 4] and virtual communities [3]. In those papers, we use a similar metaphor: a normative system can be de- scribed as an agent. Here, we propose that groups are mod- elled as agents, too. We assume in this paper that a group is already formed and, hence, we do not consider the problem of group cre- ation (see, e.g., Smith and Cohen [25]) or its dynamics. Moreover, we do not consider the problem of distributed planning in a group. The structure of this paper is the following: in Section 2, we describe the attribution of mental attitudes to a group. Then, in Sections 3 and 4, we present the formal frame- work. In Section 5, we apply the framework to some sce- narios typical of cooperation. A summary closes the paper.