A Dynamic Agents’ Behavior Model for Computational Trust Maria Joana Urbano, Ana Paula Rocha, and Eug´enio Oliveira LIACC / Departamento de Engenharia Inform´atica Faculdade de Engenharia, Universidade do Porto Rua Dr. Roberto Frias, 4200-465 Porto, Portugal {joana.urbano,arocha,eco}@fe.up.pt Abstract. The development of computational trust models is growing in attention in the community of multi-agent systems and these models are currently seen as of extreme importance in social networks, electronic business and grid computing, among others. However, one of the biggest limitations in validating the existing computational trust models is the absence of realistic models of the behavior of agents. In fact, most of the work done in this area assumes that agents behave following simple and static probabilistic models. In this paper, we present a formal model of behavior of business agents that entail in inter-organizational exchanges, taking as basis diverse literature on socio-economic theories. With this model, we empirically show that some of the computational trust ap- proaches which are more cited in the literature are not able to capture the temporal dynamics in the behavior of the business agents. Based on the results obtained from this study, we enumerate different properties that must be present in computational trust models in order to couple with realistic agents’ behavior. Keywords: Computational Trust, Behavior Models. 1 Introduction Trust is a complex issue that is being studied in several areas of research, from sociology and psychology to economics and computer science. In computer sci- ence, computational models of trust and reputation are being proposed in or- der to support several processes associated with the decision making in social networks, electronic business and distributed resources. Namely, processes that imply the contact with strangers, where uncertainty and vulnerability, as well as the associated risk, are high. In the concrete case of business exchanges, uncertainty is hard to reduce through personal relations. In the same way, vulnerability is also hard to reduce due to the presence of power relations [2] and to the existence of information asymmetry. Uncertainty and vulnerability leads to opportunism, which, in the words of Wathne and Heide (2000), can be defined as “some form of cheating or undersupply relative to an implicit or explicit contract” [14]. L. Antunes and H.S. Pinto (Eds.): EPIA 2011, LNAI 7026, pp. 536–550, 2011. c  Springer-Verlag Berlin Heidelberg 2011