Generalized Trust Propagation with Limited Evidence

Trust underlies effective interactions among autonomous parties. Ideally, a truster would base its trust in a trustee on the evidence of prior experiences with the trustee. But, such experiences arise between only a few trusters and trustees. Thus, a truster must rely upon the propagation of trust through a path of intermediary agents, each providing a trust assessment in the next. However, existing propagation approaches fail in settings such as social communities and product evaluations where a forward path isn’t available and we must consider a backward path from a rated entity to a rater. We propose Shin, a generalized trust propagation approach that incorporates a recent probabilistic method for revising trust estimates in trustees. Shin yields higher prediction accuracy than traditional approaches. In settings such as e-commerce and social networks, trust provides the basis for interaction among autonomous agents [1, 2, 3, 4, 5, 6]. We define a truster’s trust in a trustee as the truster’s belief that a future interaction with the trustee will yield expected outcomes [7]. Trust relationships naturally form a trust network, a weighted directed graph whose vertices represent agents and whose edges represent directed trust relationships, weighted with the level of trust. Each edge weight is affected by the outcomes of prior interactions and determines whether its source agent elects to pursue a future interaction with its target. A centralized reputation system consolidates the trust network. In a decentralized setting, each agent knows of only its own out-edges. A truster can reasonably decide whether to interact with a (prospective) trustee based on its estimation of the latter’s trustworthiness. A truster that lacks direct experience with a trustee would rely upon referrals leading to witnesses who provide testimony of their experiences with the trustee. Restricting the witnesses to direct experience helps avoid double counting evidence. Trust propagation [8, 9] means estimating trust over referral paths. Existing approaches consider only forward paths wherein each agent trusts the next. Our propagation technique, Shin (from the Chinese word for trust), applies even if no suitable forward path exists provided a path from both the truster and trustee to a common neighbor exists.