Reputation Systems: An Axiomatic Approach

Reasoning about agent preferences on a set of alternatives, and the aggregation of such preferences into some social ranking is a fundamental issue in reasoning about uncertainty and multi-agent systems. When the set of agents and the set of alternatives coincide, we get the so-called reputation systems setting. Famous types of reputation systems include page ranking in the context of search engines and traders ranking in the context of e-commerce. In this paper we present the first axiomatic study of reputation systems. We present three basic postulates that the desired/aggregated social ranking should satisfy and prove an impossibility theorem showing that no appropriate social ranking, satisfying all requirements, exists. Then we show that by relaxing any of these requirements an appropriate social ranking can be found. We first study reputation systems with (only) positive feedbacks. This setting refers to systems where agents' votes are interpreted as indications for the importance of other agents, as is the case in page ranking. Following this, we discuss the case of negative feedbacks, a most common situation in e-commerce settings, where traders may complain about the behavior of others. Finally, we discuss the case where both positive and negative feedbacks are available.Comment: Appears in Proceedings of the Twentieth Conference on Uncertainty in Artificial Intelligence (UAI2004

Conditional, hierarchical, multi-agent preferences

ABSTRACT. We develop a revealed-preference theory for multiple agents. Some features of our construction, which draws heavily on Jeffrey's utility theory and on formal constructions by Domotor and Fishburn, are as follows. First, our system enjoys the "small-worlds " property. Second, it represents hierarchical preferences. As a result our expected utility representation is reminscent of type constructions in game theory, except that our construction features higher order utilities as well as higher order probabilities. Finally, our construction includes the representation of conditional preferences, including counterfactual preferences. 1