This document summarizes a lecture on social information retrieval. It discusses social search, which takes social networks into account. One study examined questions people ask their social networks on Facebook and Twitter. It found questions were short, directed to "anyone", and about acceptable topics like relationships. Fast responses were considered helpful. Centrality measures like degree, closeness, and betweenness are used to determine important nodes in social networks. Strong and weak ties play different roles in information diffusion. Tie strength can be estimated using topology, neighborhood overlap, and profile/interaction data.

1. CSE509: Introduction to Web Science and Technology Lecture 6: Social Information Retrieval ArjumandYounus Web Science Research Group Institute of Business Administration (IBA)

2. Last Time… Transition from Web 1.0 to Web 2.0 Social Media Characteristics Part I: Theoretical Aspects Social Networks as a Graph Properties of Social Networks Part II: Getting Hands-On Experience on Social Media Analytics Twitter Data Hacks Part III: Example Researches August 13, 2011

3. Today Role of Today’s Web: Changing the way Information Needs are Satisfied Social Search Research Case by Microsoft Research: What do People Ask their Social Networks Techniques for Influence Analysis in Social Networks August 13, 2011

4. Role of Today’s Web August 13, 2011 Marketing Tool Information Finding Tool Media Tool

5. New Dimensions in Search with The Social Web Information Overload Search engines don’t always hold answers that users are looking for Smart Search (CNN Money) “The Web, they say, is leaving the era of search and entering one of discovery. What’s the difference? Search is what you do when you’re looking for something. Discovery is when something wonderful that you didn’t know existed, or didn’t know how to ask for, finds you.” August 13, 2011 What does that mean for search engines? Will they be left behind?

6. Role of Today’s Web August 13, 2011 Marketing Tool Information Finding Tool Media Tool

7. Social Search Takes into account the “social graph” of the person initiating the query Search activity in which users pose a question to their social networks Search systems using statistical analytics over traces left behind by others Conducting a search over an existing database of content previously provided by other users such as searching over the collection of public Twitter posts or searching through an archive of questions and answers August 13, 2011

8. Social Search Benefits Reduced impact of link spamby lesser reliance on link structure of Web pages Increased relevance due to each result being selected by users Web pages relevance judged from reader’s perspective rather than author’s perspective More current results through constant feedback August 13, 2011 Improvements achieved by social search have not been quantified so far

9. What Do People Ask Social Networks? Meredith Ringel Morris, MSR Jaime Teevan, MSR Katrina Panovich, MIT August 13, 2011

10. Questions about People’s Questions What questions do people ask? How are the questions phrased? What are the question types and topics? Who asks which questions and why? Which questions get answered? How is answer speed and utility perceived? What are people’s motivations for answering? August 13, 2011

11. Survey of Asking via Status Messages Survey content Used a status message to ask a question? Frequency of asking, question type, responses received Provide an example Answered a status message question? Why or why not? Provide an example 624 participants Focus on Facebook and Twitter behavior August 13, 2011

12. Questions: Types August 13, 2011

13. Questions: Topics Missing: Health, Religion Politics, Dating, and Finance August 13, 2011

14. Questions: Who Asks What August 13, 2011 men old Twitter women Facebook young

15. Questions: Motives for Asking August 13, 2011

16. Questions About People’s Questions What questions do people ask? How are the questions phrased? What are the question types and topics? Who asks which questions and why? Which questions get answered? How is answer speed and utility perceived? What are people’s motivations for answering? August 13, 2011

17. Answers: Speed and Utility 94% of questions received an answer Answer speed A quarter in 30 minutes, almost all in a day People expected faster, but satisfied with speed Shorter questions got more useful responses Answer utility 69% of responses helpful August 13, 2011

18. Answers: Speed and Utility Fast No correlation Unhelpful August 13, 2011

19. Answers: Motives for Answering Motives for Not Answering - Don’t know the answer - Private topic - Question impersonal August 13, 2011

20. Answers About People’s Questions The questions people ask Short, directed to “anyone” Subjective questions on acceptable topics Social relationships important motivators The questions that get answered Fast, helpful responses, related to length and type Answers motivated by altruism and expertise August 13, 2011

21. Enhancing Search using Social Network Features Recency Crawling and Ranking Identification of Hot Topics on Social Web [YQG+11] News in the Making Trend analysis Event detection Real-Time Search Information Diffusion and Influence Analysis Community Detection Opinion Mining August 13, 2011

22. August 13, 2011 Nodes, Ties and Influence

23. Importance of Nodes Not all nodes are equally important Centrality Analysis Find out the most important nodes in one network Commonly-used Measures Degree Centrality Closeness Centrality Betweenness Centrality Eigenvector Centrality August 13, 2011

24. Degree Centrality The importance of a node is determined by the number of nodes adjacent to it The larger the degree, the more import the node is Only a small number of nodes have high degrees in many real-life networks Degree Centrality Normalized Degree Centrality: For node 1, degree centrality is 3; Normalized degree centrality is 3/(9-1)=3/8. August 13, 2011

25. Closeness Centrality “Central” nodes are important, as they can reach the whole network more quickly than non-central nodes Importance measured by how close a node is to other nodes Average Distance Closeness Centrality August 13, 2011

26. Closeness Centrality Example Node 4 is more central than node 3 August 13, 2011

27. Betweenness Centrality Node betweenness counts the number of shortest paths that pass one node Nodes with high betweenness are important in communication and information diffusion Betweenness Centrality The number of shortest paths between s and t The number of shortest paths between s and t that pass vi 26 August 13, 2011

28. Betweenness Centrality Example The number of shortest paths between s and t The number of shortest paths between s and t that pass vi August 13, 2011

29. Eigenvector Centrality One’s importance is determined by his friends’ If one has many important friends, he should be important as well. The centrality corresponds to the top eigenvector of the adjacency matrix A. A variant of this eigenvector centrality is the PageRank score. August 13, 2011

30. Weak and Strong Ties In practice, connections are not of the same strength Interpersonal social networks are composed of strong ties (close friends) and weak ties (acquaintances) Strong ties and weak ties play different roles for community formation and information diffusion Strength of Weak Ties (Granovetter, 1973) Occasional encounters with distant acquaintances can provide important information about new opportunities for job search August 13, 2011

32. Learning from Network Topology Bridges connecting two different communities are weak ties An edge is a bridge if its removal results in disconnection of its terminal nodes e(2,5) is a bridge e(2,5) is NOT a bridge August 13, 2011

33. “shortcut” Bridge Bridges are rare in real-life networks Alternatively, one can relax the definition by checking if the distance between two terminal nodes increases if the edge is removed The larger the distance, the weaker the tie is d(2,5) = 4 if e(2,5) is removed d(5,6) = 2 if e(5,6) is removed e(5,6) is a stronger tie than e(2,5) August 13, 2011

34. Neighborhood Overlap Tie Strength can be measured based on neighborhood overlap; the larger the overlap, the stronger the tie is -2 in the denominator is to exclude vi and vj August 13, 2011

35. Neighborhood Overlap Tie Strength can be measured based on neighborhood overlap; the larger the overlap, the stronger the tie is -2 in the denominator is to exclude vi and vj August 13, 2011

36. Learning from Profiles and Interactions Twitter: one can follow others without followee’s confirmation The real friendship network is determined by the frequency two users talk to each other, rather than the follower-followee network The real friendship network is more influential in driving Twitter usage Strengths of ties can be predicted accurately based on various information from Facebook Friend-initiated posts, message exchanged in wall post, number of mutual friends, etc. Learning numeric link strength by maximum likelihood estimation User profile similarity determines the strength Link strength in turn determines user interaction Maximize the likelihood based on observed profiles and interactions 35 August 13, 2011