Paper Study – Propagation of Trust in E-commerce Communities, and others YuanDa Cao （曹元大）, etc. Beijing Institute of Technology Presented by Vincent Dec/2004

Web of Trust: Trust quantification, inference and propagation e.g. what is trust propagation [Guha 04] --- subjective! : beliefs of your trusted acquaintance/stranger, might from beliefs of his/her trusted acquaintance/stranger Importance to E-commerce 1.Security issues in open, anonymous, pervasive networks / communities 2.Not well established trust system for E-commerce compared with normal commerce (Josang) 3.Some initiative of applying trust to E-commerce has positive feedback Relevance to Computer Science (Lik Mui - thesis) 1.Dynamics of Reciprocity, Trust and Reputation in virtual communities 2.AI borrows from Economics in modeling rationality and intelligence, it is time for both to deal with social quantities like norms, morals, preferences, etc.

Importance to other fields: Distributed Systems [Mui 02] P2P Network e.g. [EigenTrust-03] for Reputation Management Assign each peer a unique global trust value Based on Power iteration To decrease the number of downloads of inauthentic files

Classification of Trust: Formal Trust, Informal Trust (Mui-thesis) Formal: e.g. legislation, contracts, escrow Direct Trust, Recommendation Trust (Beth99, Abdul-Rahman00) Direct: agent-specified values/scales about another agent Recommended trust: they consider as reputation This paper: Trust: a subjective expectation to a target agent’s future behavior reputation trustreciprocity net benefit Note:[Mui-02]Trust: A subjective expectation an agent has about another’s future behavior based on the history of their encounter Other terms involved: credibility, belief, usability, rating, etc.

Quantification & Inference of Trust: 1.Beth99: using previous positive and negative experiences 2.Josang: using subjective logic and D-S theory 3.Mui – theisis: reputation and history T= (p+c 1 )/(n+ c 1 + c 2 ) [p: cooperation, n: encounter] 4.This paper: T=(g+1)/(g+b+2) [g: successful experience, b: fail] and (trust strength S): the credibility of T But sections 3.1, 3.2, 3.3 are not clearly stated, some comments are: 3.1: direct interaction? The sentence “Trust discounting in ….” why S kj =1, S ik not? T ijk seems to relate to (T kj, S ik S kj ) why neglect T ik 3.2: S ijA is not defined clearly 3.3: 0.4 in the example is T, not S, so how to use formula (4)

Paralleling the trust network to get multiple paths Graph transforming algorithm [Mui-thesis] This paper has a modification to the transforming algorithm, to avoid recalculating the contribution of nodes immediately preceding the target node (e.g 10, 9, 11, 7) [direct experiment?] Propagation & Combination of Trust: - Parallelizing the trust network

1.Along each path, there is trust discount due to propagation 2.Paths have different weights when combined Guha04 and this paper: weighted average method This paper: \sum( ST) / sum(S) [Mui-02] not clear the discounting weighted combination: T(path i) * mean( prod(weights along path i)) Bin02, Josang: Dempster-shafer theory Propagation & Combination of Trust: - Combining the trust from multiple paths

Dempster-shafer theory [Binyu 02 Example] Trust Distrust Uncertain A to jm A ({T})=0.8, m A ({~T})=0, m A ({T,~T})=0.2 B to jm B ({T})=0.9, m B ({~T})=0, m B ({T,~T})=0.1 j A B Cumulative belief regarding j: ґ j ({T}) = 0.8* * *0.1 = 0.98 ґ j ({~T}) = 0 ґ j ({T,~T}) = 0.02 The reputation of j is defined as: ґ j ({T}) - ґ j ({~T}) = 0.98 Controversial to get reputation 0.98 > either 0.9 or 0.8 Combination of Trust: - Combining the trust from multiple paths Not sure about the propagation discount

Conclusion and comments 1.A good try to study trust in E-commerce, but the context of E-commerce is weakly situated. And some introduction words copied/modified from [Guha04] 2.Concise analysis on related work, the division of quantification, propagation, and combination of trust 3.The core part is not clearly stated though the structure can be somehow understood, especially for some notation, and the underlying reasons of introducing some new notations/approaches.