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SOCIAL NETWORKS ANALYSIS SEMINAR INTRODUCTORY LECTURE Danny Hendler and Yehonatan Cohen Advanced Topics in on-line Social Networks Analysis Slide 2 Seminar requirements Select a paper and notify me by March, 17'th Study the paper well and prepare a good presentation Give an excellent seminar talk Participate in at least 80% of seminar talks Slide 3 Seminar schedule Introductory lecture #1 5/3/14 No seminar (Purim!) Semester ends 12/3/14 Introductory lecture #2 Papers list published, students send their 3 preferences 14/3/14 11 weeks of Student talks 19/3/14 Student talks start All students preferences must be received 10/3/14 26/3/14 Slide 4 Talk outline Social networks Properties of on-line social networks Small-world phenomenon Power-law distribution Community structure Community detection Slide 5 Social networks What is a social network? A network, were nodes represent actors and edges represent interactions/relationships Slide 6 Social networks: an example Slide 7 Giant component Slide 8 Social networks: an example Some nodes are very active Slide 9 Types of online social media Slide 10 Top 20 USA websites 1Google.com11Blogger.com 2Facebook.com12msn.com 3Yahoo.com13Myspace.com 4YouTube.com14Go.com 5Amazon.com15Bing.com 6Wikipedia.org16AOL.com 7Craigslist.org17LinkedIn.com 8Twitter.com18CNN.com 9Ebay.com19Espn.go.com 10Live.com20Wordpress.com Source: Alexa report, February, 2014 Slide 11 Top 20 USA websites 1Google.com11Blogger.com 2Facebook.com12msn.com 3Yahoo.com13Myspace.com 4YouTube.com14Go.com 5Amazon.com15Bing.com 6Wikipedia.org16AOL.com 7Craigslist.org17LinkedIn.com 8Twitter.com18CNN.com 9Ebay.com19Espn.go.com 10Live.com20Wordpress.com 30% social network sites Source: Alexa report, February, 2014 Slide 12 Top 20 USA websites 1Google.com11Blogger.com 2Facebook.com12msn.com 3Yahoo.com13Myspace.com 4YouTube.com14Go.com 5Amazon.com15Bing.com 6Wikipedia.org16AOL.com 7Craigslist.org17LinkedIn.com 8Twitter.com18CNN.com 9Ebay.com19Espn.go.com 10Live.com20Wordpress.com 30% social network sites 30% additional sites with social network aspects Source: Alexa report, February, 2014 Slide 13 Social networks Properties of on-line social networks Small-world phenomenon Power-law distribution Community structure Community detection Properties of social networks Slide 14 Milgram's small world phenomenon experiment (1967) Six degrees of separation:I read somewhere that everybody on this planet is separated by only six other people. Six degrees of separation between us and everyone else on this planet. (*) (*) John Guare. Six Degrees of Separation: A Play. Vintage Books, 1990. So, Milgram decided to check Slide 15 Milgram's experiment (cont'd) Budget: $680!!! A set of starters, all try to forward a letter to a single target person Starters notified of targets name/address/occupation Must forward letter to someone known on first-name basis Image taken from Wiki. Slide 16 Milgram's experiment: results 64 chains arrived Median length: 6 Taken from: Networks, crowds and Markets, D. Easley & J. Kleinberg. (Book is online) Slide 17 A slightly more modern example (2008) Slide 18 Social networks Properties of on-line social networks Small-world phenomenon Power-law distribution Community structure Community detection Properties of social networks Slide 19 A matter of popularity As a function of k: what fraction of Web pages have k in-links? ~1/k 2.1 (*) (*) Broder et al. Graph structure in the Web. WWW 2000, pp. 309-320. Slide 20 The power low distribution Degrees Nodes A.k.a. long tail distribution, scale-free distribution Most nodes have low degrees Few nodes have extremely high degrees Slide 21 Web pages in-degree: log-log scale Slide 22 Some more examples Friendship Network in FlickrFriendship Network in YouTube Slide 23 Why is popularity power-law? Slide 24 A simple game Procedure for creating Web page j {1,2N} Choose page i