Nonmonotonic Trust Management for P2P Applications

Community decisions about access control in virtual communities are non-monotonic in nature. This means that they cannot be expressed in current, monotonic trust management languages such as the family of Role Based Trust Management languages (RT). To solve this problem we propose RT-, which adds a restricted form of negation to the standard RT language, thus admitting a controlled form of non-monotonicity. The semantics of RT- is discussed and presented in terms of the well-founded semantics for Logic Programs. Finally we discuss how chain discovery can be accomplished for RT-.Comment: This paper appears in the proceedings of the 1st International Workshop on Security and Trust Management (STM 2005). To appear in ENTC

Strategic delegation in experimental duopolies with endogenous incentive contracts

Often, deviations of firm behavior from profit maximization are the result of managerial incentive contracts. We study the endogenous emergence of incentive contracts used by firm owners to delegate the strategic decisions of the firm. These contracts are linear combinations either of own firm's profits and revenues, or own and rival firms' profits. A two- and three-stage game are studied depending on whether owners commit or not to a certain contract type before setting the managerial incentives and the level of output to produce in the market. We report experimental results which confirm some of the predictions of the model, especially those concerning owners' preference for relative performance incentives over profit-revenue contracts. Neglected behavioral aspects are proposed as possible explanation of some divergence between the theory and the experimental evidence, more specifically the relation between contract terms and managers' output choicesExperimental economics; Oligopoly theory; Managerial delegation; Endogenous contracts.

Bargaining with commitments

We study a simple bargaining mechanism in which each player puts a prize to his resources before leaving the game. The only expected final equilibrium payoff can be defined by means of selective marginal contributions vectors, and it coincides with the Shapley value for convex games. Moreover, for 3-player games the selective marginal contributions vectors determine the core when it is nonempty.demand commitment game bargaining

Common Agency Equilibria with Discrete Mechanisms and Discrete Types

This paper characterizes the equilibrium sets of an intrinsic common agencygame with discrete types and direct revelation mechanisms. After presentinga general algorithm to find the pure-strategy equilibria of this game, we use itto characterize these equilibria when the two principals control activitieswhich are complements in the agent’s objective function. Some of thoseequilibria may entail allocative inefficiency. For the case of substitutes, wedemonstrate non-existence of such equilibria with direct mechanisms, butexistence may be obtained with indirect mechanisms. Finally, we relax theequilibrium concept and analyze quasi-equilibria. We show that existence isthen guaranteed and characterize the corresponding allocations.

Trust models in ubiquitous computing

We recapture some of the arguments for trust-based technologies in ubiquitous computing, followed by a brief survey of some of the models of trust that have been introduced in this respect. Based on this, we argue for the need of more formal and foundational trust models

A Model of Dynamic Resource Allocation in Workflow Systems

Current collaborative work environments are characterized by dynamically changing organizational structures. Although there have been several efforts to refine work distribution, especially in workflow management, most literature assumes a static database approach which captures organizational roles, groups and hierarchies and implements a dynamic roles based agent assignment protocol. However, in practice only partial information may be available for organizational models, and in turn a large number of exceptions may emerge at the time of work assignment. In this paper we present an organizational model based on a policy based normative system. The model is based on a combination of an intentional logic of agency and a flexible, but computationally feasible, non-monotonic formalism (Defeasible Logic). Although this paper focuses on the model specification, the proposed approach to modelling agent societies provides a means of reasoning with partial and unpredictable information as is typical of organizational agents in workflow system