©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Trust-Aware Delivery of Composite Goods Zoran Despotovic, Karl Aberer EPFL-I&C Distributed Information Systems Laboratory {zoran.despotovic,

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Setting – Safe Exchange Exchanges with two participants: the supplier (seller) and the consumer The supplier is supplying and selling the set of goods to the consumer - the price to be paid Both value functions ( and ) known to the both partners The value functions additive (change with a delivery only for the partners’ valuations of the delivered item) Problem: can the deliveries of goods and money be arranged in such a way that, at any step during the exchange, both partners are better off by continuing the exchange than breaking it.

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis When Does a Safe Exchange Sequence Exist? Two bounds (supplier’s and consumer’s) defined: and A safe exchange exists if and only if there exists an order such that, for any :

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Reputation and Trust Management Reputation and trust management reference model: Reputation management – collect information about past behavior of each member and spread it for others to use Trust management – calculate predictions of the future behavior Decision making – decide whether to interact or not and feed the result of the interaction back to the reputation management module Trust Management Reputation Management Decision Making

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Trust-Aware Extension Fully trustworthy partners, with excellent reputation records, cannot carry out an exchange only due to their valuations of the goods Assumption: probabilities of honest behavior of the partners obtained from the underlying trust model Expected utility inputs from the partners (min values)

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis New Existence Conditions New conditions for trust-aware safe exchange feasibility derived and

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Algorithm

©2002, Zoran Despotovic, Karl Aberer, EPFL-I&C, Laboratoire de systèmes d'informations répartis Potential Limitations Divisibility of the goods –An example – movie files: the fact that the whole movie file has been delivered has an additional value. This can be modeled by a fictitious chunk at the end of the exchange Additive utilities Known valuations of the goods –Approximations: the price a seller can obtain on the market; the popularity of the goods for consumers Constant probabilities