trusis: trust accross social network
DESCRIPTION
In this talk we shall introduce the main ideas of TruSIS (Trust in Social Internetworking System), a Marie Curie Fellowhsip financed by European Union and hosted at VU University, Department of Computer Science, Business and Web group. The goal of TruSIS is to study the baheviour of users who affiliate to multiple social networking sites and are active in them (e.g., users may publish personal profiles on sites like MySpace and post videos on sites like YouTube). We briefly called this scenario as SIS (Social Internetworking system). As a first research contribution, we implemented a crawler to gather data about users and link their profiles on multiple social networking websites. To this purpose we used Google Social Graph API, a powerful API released by Google in 2008. We obtained a sample of about 1.3 millions of user accounts and 36 millions of connections between them. Parameters from social network theory (like average clustering coefficient, network modularity and so on) were used to study the structural properties of the gathered sample and how these properties depend on user behavious. A second contribution is about the computation of distance between two users in a SIS on the basis of their social ties. We used a popular parameter from Social Network Theory known as Katz coeffcient and provide a computationally afficient approach to computing Katz coefficient which relies on the usage of a popular tool from linear algebra known as Sherman- Morrison formula. Finally, we shall describe our work on extending the notion of trust from single social networks to a SIS. We describe the main research challenges tied to the definition of trust and how they relate to Semantic Web technologies.TRANSCRIPT
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TruSiS: Trust in Cross Social Networks Lora Aroyo Pasquale De Meo
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Social Networking
• Explosive growth in number of sites and users – Facebook 350 mil users (bigger than US), the third biggest country (Feb 2010)
– Used for adverEsing, public life, etc
• Social Networking APIs to gather data on users, their relaEonships and acEviEes – Leskovec & Horowitz (WWW‘08) analyzed 240 mil MSN contacts
– Kwan et al. (WWW‘10) analyzed the whole TwiVer
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Social Network Analysis
• Study collecEve human behaviour on a large scale, e.g. – How node degree is distributed? – Do small world phenomenon emerge?
– Are nodes clustered into groups? – What are the different user informaEon sharing tasks?
– How do they connect with different communiEes?
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Social Internetworking
• Users affiliate to mulEple social spaces – e.g. UK adults have ~1.6 online profiles, and 39% of those with one profile have at least two other profiles
• Pla`orm(s) for data portability among social networks
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Social Internetworking System
• Provide mechanisms to: – help users find reliable users – disclose malicious users/spammers
– sEmulate the level of user parEcipaEon
– deal with trust in linked data – deal with different contexts and policies for accessing, publishing and re-‐distribuEng data
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What do we aim for …
• model to represent Social Internetworking components & their rela4onships
• understand Social Internetworking structural proper4es and see how it differs from tradiEonal social networks
• model to compute trust & reputa4on based on linked data
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Some requirements …
• Trust -‐ 4ed to user’s performance, i.e., beneficial contribuEons to other users
• Users are involved in a range of ac4vi4es, e.g., tagging, posEng comments, raEng
• A range of heterogeneous en44es, e.g. users, resources, comments, raEngs and their interacEons (vs. single role nodes in graphs)
• Edges need to support n-‐ary rela4onships • Mul4-‐dimensional network
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SIS Pilot 1
• Social Web Crawler – Google Social Graph API – XFN and FOAF markups; me edges, i.e., accounts located in different social networks referring to the same individual
• BFS of Social Web – 1 305 112 user accounts – 36 278 838 connecEons between user accounts
Flickr
Twitter LiveJournal Others
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Goal of the Pilot
The pilot has three main goals:
• relaEonship between structural properEes of a SIS and human behaviour
• how can we take advantage of global knowledge harnessed in a SIS
• how these results contribute to the TruSIS trust definiEon
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Goal of the Pilot
Goal 1: We found that some structural properEes of a SIS can be explained in terms of user behaviours:
Example: node degree distribuEon shows a power law indicaEng that few users are quite acEve (e.g., they rate many objects, post many comments, and so on) while the vast majority is almost inacEve.
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Goal of the Pilot Goal 2: We found that knowledge
in a SIS is useful to solve cold start problems.
For instance assume a user u joins a social network like Flickr and he has no contacts
Idea: Find users of SIS who are close to “u” and are affiliated to Flickr (bootstrap user).
Suggest them to u.
Problem: When two users are close in a SIS? It turns to a known problem “when two nodes in a graph are close”?
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Goal of the Pilot
• Goal 3: ConnecEvity properEes are at the basis of many algorithms to comput etrust in social networks (Golbeck 2006, Ziegler 2005, Leskovec, HuVenlocker & Kleinberg, 2010).
• We plan to use closeness to propagate trust values.
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Pilot 1: Contact Graph Analysis
• Average Clustering Coefficient (ACC) to assess the tendency of nodes to form cliques
• High compared to other graphs – reflects the high chance that two users are “friends” as there is a third person who is also their “friend”
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Pilot 1: Contact Graph Analysis
• edge distribuEon in CG – A power law emerged exponent about 1.65
• distribuEon of me edges – exponent about 3.39
• Why? – mulEple idenEEes in mulEple social spaces but no connecEons between them
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Pilot 1: Contact Graph Analysis
• High Network Modularity – nodes appear clustered in groups
• Can we export knowledge of the user from one network to another (in terms of trust & reputaEon)?
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Calculating Closeness
• aggregaEng informaEon from different social networks to determine how ‘close’ are users
• degree of closeness of two users -‐ Katz coefficient (Katz, 1953) – # of users is big
• algorithm where SIS is parEEoned in small communiEes plus with Sherman Morrison
• Experimental trials show that: • We achieve significant Eme savings • The approximaEon error is quite small
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Our Definition of trust in SIS (1)
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In other words …
• Trust is defined in the context of: – Reputa4on (of user) in a social network – Impact (of user) in a social network
– Authority (of user or organizaEons)
• Trust as a binary rela4onship between users (e.g. A trusts B) based on user acEviEes: – frequency, quality and type of users contribuEons – etc.
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For example: Reputation
• users post resources & rate resources posted by others
• To compute reputaEon we assume that: – User-‐high-‐reputaEon if the user authors high quality resources
– Resource-‐high-‐quality if it gets a high average raEng & posted by users with high reputaEon
• mutual reinforcement principle
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Trust in SIS
• n = # of users m = # of resources authored
• r(i) = reputaEon of useri • q(j) = quality of resourcej • e(j) = average raEng of resourcej • Aij = 1 if useri posted a resourcej 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 idenEty matrix)
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What do we try to expore …
• The role of SW in the definiEon, idenEficaEon and reasoning with trust, reputaEon, impact and authority? (e.g., Linked Open Data)
• The role of trust, reputaEon, impact and authority in event models, e.g. SEM and user models, e.g. FOAF
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Among others, we still need to …
• Gather a larger amount of data to analyze further the structural properEes of SIS
• Test the effecEveness of the approach for trust, reputaEon, impact and authority compuEng
• Test with real users in the social space of Agora (Social Event-‐based History browsing) and in PrestoPrime (Social SemanEc Tagging)
• Ontology-‐based model of trust and reputaEon in different domains (with LOD)
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The team
• DIMET – University of Reggio Calabria, Italy – Pasquale De Meo
– Domenico Ursino
• External collaborator – University of Torino – Federica Cena