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Presentation at the SASweb2010 Workshop at UMAP2010 conference
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Trust and Reputation in Social Internetworking Systems
Lora Aroyo1
Pasquale De Meo1
Domenico Ursino2
1VU University Amsterdam, the Netherlands 2DIMET – University of Reggio Calabria, Italy
Social Networks Added Value
! advertise products and disseminate innovations & knowledge ! find information relevant to users
! find relevant users, e.g. LinkedIn
! spread opinions, e.g., personal, social or political
! interesting for: ! museums, broadcaster, government institutions
Online Identities
! Increasing number of identities ! different information sharing tasks ! connect with different communities
! UK adults have ~1.6 online profiles
! 39% of those with one profile have at least two other profiles
! Companies exploring the potential of social internetworking
! Platform(s) for data portability among social networks
Social Internetworking System
© danbri
What’s Needed?
! mechanisms to: ! help users find reliable users
! disclose malicious users or spammers
! stimulate the level of user participation ! deal with trust in linked data
! deal with different contexts and policies for accessing, publishing and re-distributing data
What’s the Goal?
! model to represent Social Internetworking components & their relationships
! understand Social Internetworking structural properties and see how it differs from traditional social networks
! model to compute trust & reputation based on linked data
Requirements
! trust should be tied to user’s performance, i.e., providing beneficial contributions to other users
! consider that users are involved in a range of activities, e.g., tagging, posting comments, rating
! represent a wide range of heterogeneous entities, e.g. users, resources, posts, comments, ratings and their interactions (vs. single role nodes in graphs)
! edges need to support n-ary relationships vs. binary in graphs
! multi-dimensional network vs. one-dimensional in graphs
! easy to manipulate and intuitive model
Graph-Based Approaches
! Model user community as graph G ! edges reflect explicit trust relationship between
users
! G is sparse, thus often need for inferring trust values
! model trust & reputation in force-mass-acceleration style capture all factors and combine them in a set of equations
! resulting model is too complicated to be handled
Link-Based Approaches
! link analysis algorithms, e.g. PageRank or HITS, model trust as a measure of system performance, e.g., number of corrupted files in a peer of a P2P network
! attack-resistant to manipulate reputation score
! model trust & reputation in force-mass-acceleration style capture all factors and combine them in a set of equations
! resulting model is too complicated to be handled
SIS Approach
! Social Graph API (list of public URLs and connections for person p (e.g., Twitter page of p and contacts of p)
! Hypergraph
! nodes labels with object role
! multiple hyperedges between two nodes
! hyperedges – link two or more entities
SIS Pilot: Analysis
! We gathered from multiple social networks, e.g., LiveJournal, Twitter, Flickr: ! 1, 252, 908 user accounts
! 30, 837, 012 connections between users ! The probability P(k) that a user has created an
account in k networks is distributed as: P(k) ~ k-4.003
! Few users are affiliated to multiple networks
! More than 90% of users are affiliated to less than 3 networks
Canonization Procedures
! Map gathered data to graph with following properties:
! High network modularity, i.e., nodes tend to form dense clusters with few inter-cluster edges
! Small world phenomenon, i.e., paths between arbitrary pairs of nodes are usually short
Reputation in SIS
! Setting: ! users post resources &rate resources posted by others
! To compute reputation we assume that: ! User-high-reputation if he authors high quality resources
! Resource-high-quality if it gets a high average rating & posted by users with high reputation
! mutual reinforcement principle
.
Trust in SIS
! n = # of users in SIS m = # of resources they authored
! r(i) = reputation of useri q(j) = quality of resourcej
! e(j) = average rating of resourcej
! Aij = 1 if useri posted a resourcej and Aij = 0 otherwise
! r = Aq and q = AT r + e r = (I – AAT)-1Ae
! compute dominant eigenvector of a symmetric matrix
! easy to compute even if A gets large (AT = transpose of A and I = nxn identity matrix)
.
Future Work
! Gather a larger amount of data to analyze further the structural properties of SIS
! Test the effectiveness of the approach for reputation computing
! Test with real users in the social space of Agora (Social Event-based History browsing) and in PrestoPrime (Social Semantic Taging)
! Ontology-based model of trust and reputation in different domains (with LOD)
! This research is funded by EU Marie Curie Fellowship Grant
Acknowledgements