Measurement and Analysis of Online Social Networks Alan Mislove,Massimiliano Marcon, Krishna P. Gummadi, Peter Druschel, Bobby Bhattacharjee Presented by Aleksandra Potapova

Focus graphs of online social networks – how they were obtained – how they were verified how measurement and analysis was performed properties of obtained graphs why these properties are relevant

What was studied? Flickr YouTube LiveJournal, Orkut

Why should we perform measurements and analysis in social networks? To design future online social network based systems To understand the impact of online social networks on the Internet To reduce the number of spam To improve security aspect

5 Summary of graph properties small-world power-law scale-free correlation between indegree and outdegree large strongly connected core of high-degree nodes surrounded by small clusters of low- degree nodes

Crawling Algorithms for large graphs BFS and DFS Snowball method(crawling only small subset of a graph by ending BFS early): – Partial BFS craws overestimate node degree and underestimate the level of symmetry. – In social networks, they underestimate the power- law coefficient, but closely match other metrics such as overall clustering coefficient.

How social networks should be crawled? The focus of the paper – WCC – Forward and reverse links should be used

How the graphs were obtained? API – users – groups – forward/backward links HTML Screen Scraping

How to Verify Samples 1.Obtain a random user sample – LJ: feature which returns 5,000 random users – Flickr: random 8-digit user id generation 2.Conduct a crawl using these random users as seeds 3.See if these random nodes connect to the original WCC 4.See what the graph structure of the newly crawled graph compares to original

Crawling Concerns – FW links no effect on largest WCC

11 Crawling Concerns – FW links increasing the size of the WCC by starting at a different seed

12 SiteYTFlickrLJOrkut Users(mill) Links(mill) symmetry79.1%62.0%73.5%100.0% Access (FW: Forward- only) (SS: HTML screen- scraping) API (users only) FW SS for group info API (users + groups) FW API (users + groups) FW + BW SS for users + groups

13 Link Symmetry even with directed links, there is a high level of symmetry possibly contributed to by informing users of new incoming links makes it harder to identify reputable sources due to dilution

14 Power-law node degrees Orkut deviates: – only 11.3% of network reached (effect of partial BFS crawl – Snowball method) – artificial cap of user’s number of outgoing links, leads to a distortion in distribution of high degrees differs from Web

15 Power-law node degrees

17 Correlation of indegree and outdegree over 50% of nodes have indegree within 20% of their outdegree

18 Path lengths and diameter all four networks have short path length

19 Link degree correlations JDD: joint degree distribution(how often nodes of different degree connect to each other) K nn --- mapping between outdegree and average indegree of all nodes connected to nodes of that outdegree – Used for aproxmation of JDD YouTube different due to extremely popular users being connected to by many unpopular users Orkut shows bump due to undersampling

Measurement and Analysis of Online Social Networks 20 Joint degree distribution and Scale-free behaviour undersampling of low-degree nodes celebrity-driven nature cap on links

Measurement and Analysis of Online Social Networks 21 Densely connected core removing 10% of core nodes results in breaking up graph into millions of very small SCCs graphs below show results as nodes are removed starting with highest- degree nodes (left) and path length as graph is constructed beginning with highest-degree nodes(right) Sub logarithmic growth

Measurement and Analysis of Online Social Networks 22 Tightly clustered fringe based on clustering coefficient social network graphs show stronger clustering, most likely due to mutual friends Possibly because personal content is not shared

Measurement and Analysis of Online Social Networks 23 Groups group sizes follow power-law distribution represent tightly clustered communities

Measurement and Analysis of Online Social Networks 24 Groups Orkut special case maybe because of partial crawl

Measurement and Analysis of Online Social Networks 25 Node Value Determination Directed Graph, current model nodes with many incoming links (hubs) have value due to their connection to many users it becomes easy to spread important information to the other nodes, e.g. DNS unhealthy in case of spam or viruses in order for a user to send spam, they have become a more important node, amass friends

Questions?