Structure and Evolution of Online Social Networks

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Structure and Evolution of Online Social Networks

• Ravi Kumar Jasmine Novak Andrew Tomkins

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Our goal

• To study real online social networks and answers
  questions like
  
• How are social networks formed?
• How do they evolve?
• What properties do they exhibit?

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Data Flickr and Yahoo! 360

• Flickr (www.flickr.com)
• online photo-sharing, social networking
• graph nodes are users, edges friendships
• 1M nodes, 8M directed edges
• Yahoo! 360 (360.yahoo.com)
• social networking website
• graph nodes are users, edges are listed
  contacts
  
• 5M nodes, 7M directed edges

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Are friendships reciprocal in online social
networks?

• 70 in Flickr and 84 in Yahoo! 360

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How does density change with time?
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Degree distribution Component size distribution
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Segmenting the network three distinct regions

• Singletons
• degree-zero nodes who have joined the service,
  but have never connected to another user in the
  network
  
• Giant component
• densely connected core users, each connected to
  each other through paths in the social network
  
• Middle region
• remainder - isolated communities that connect to
  each other, but not the network at large

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How do components merge as new links/nodes are
added in network?
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Component sizes inFlickr Contacts
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Component sizes in360 Contacts
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How do components merge?
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Surprising things about the Middle Region

• These isolated communities account for a
  significant portion of the population 1/3 of
  Flickr, 1/10 of Yahoo! 360
  
• Most of these components
• form STARS! one or two
• high-degree center nodes
• connected to many low-degree twinkles
• Despite growth (10x ) and dramatic changes in
  the particular users, the fraction of the
  population in isolated communities remains
  stable!

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Characterizing the Stars in the middle region
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How does the network diameter change with time?
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The Giant Component

• Do stars form the backbone of the GC?
• No! Connectivity persists, even when stars and
  their twinkles are removed
  
• How does it grow?
• Do stars merge together to form bigger
  components, before finally joining the GC?
  
• NO! Two processes dominate singletons joining
  the GC, and stars joining the GC