Thesis full text PDF (in Italian) - Politecnico di Milano

2.4.1 Measurements and analysis of online Social Networks Thanks to the popularity of some online social network that provides a powerfulmeans of sharing, organizing, and finding content and contacts, it was possible tostudy the characteristics of the social network graphs at large scale.The analysis has been done taking into considerations publics data obtained fromdifferent social networks (YouTube, LiveJournal, Flickr and Orkut), this due tothe fact that data gathered from multiple sites enables to identify commonstructural properties [17].One of the objectives was that to try to understand if the study of the socialnetwork structure, might lead to algorithms that could detect trusted or influentialusers, much like the study of the Web graph led to the discovery of algorithms forfinding authoritative sources in the Web.An important aspect observed, was the high degree of reciprocity in directed userlinks, leading to a strong correlation between user indegree and outdegree,providing some difficulties in identifying valid information through the analysisof the only structure of the network (this differs from content graphs like thegraph formed by web hyperlinks, where the popular pages, “authorities”, and thepages with many references, “hubs”, are distinct).The analysis has highlighted that online social networks contains a large, stronglyconnected core of high-degree nodes, surrounded by many small clusters of lowdegreenodes, suggesting that high-degree nodes in the core are critical for theconnectivity and the flow of information.26