Recommender Systems with Social Regularization And Some Critical
- Slides: 27
Recommender Systems with Social Regularization And Some Critical Thinking Hao Ma, Dengyong Zhou, Chao Liu Microsoft Research Michael R. Lyu The Chinese University of Hong Kong Irwin King AT&T Labs – Research The Chinese University of Hong Kong Ting Chen Northeastern University
Recommender Systems are Everywhere 2
Web 2. 0 Web Sites are Everywhere 3
Trust-aware Recommender Systems • These Methods utilize the inferred implicit or observed explicit trust information to further improve traditional recommender systems. – [J. O’Donovan and B. Smyth, IUI 2005] – [P. Massa and P. Avesani, Rec. Sys 2007] – [H. Ma, I. King, and M. R. Lyu, SIGIR 2009] • Based on the motivation that “I trust you => I have similar tastes with you”. 4
Comparison • Trust-aware • Social-based – Trust network: unilateral relations – Social friend network: mutual relations – Trust relations can be treated as “similar” relations – Friends are very diverse, and may have different tastes – Few datasets available on the Web – Lots of Web sites have social network implementation 5
Contents of This Work • Focusing on social-based recommendation problems • Two methods are proposed based on matrix factorization with social regularization terms – Can be applied to trust-aware recommender systems. • Experiments on two large datasets – Douban (social friend network) – Epinions (trust network) 6
Problem Definition Social Network Information User-Item Rating Matrix 7
Low-Rank Matrix Factorization for Collaborative Filtering • Objective function Ui , Vj : low dimension column vectors to represent user/item preferences. 8
Social Regularization I • Average-based regularization Minimize Ui’s taste with the average tastes of Ui’s friends. The similarity function Sim(i, f) allows the social regularization term to treat users’ friends differently. 9
Social Regularization I • Gradients 10
Social Regularization II • Individual-based regularization This approach allows similarity of friends’ tastes to be individually considered. It also indirectly models the propagation of tastes. 11
Social Regularization II • Gradients 12
Similarity Function • Vector Space Similarity (VSS) or Cosine Similarity • Pearson Correlation Coefficient (PCC) 13
Dataset I • Douban – Chinese Web 2. 0 Web site with social friend network service – The largest online book, movie and music review and rating site in China – We crawled 129, 940 users and 58, 541 movies with 16, 830, 839 movie ratings – The total number of friend links between users is 1, 692, 952 14
Dataset II • Epinions – A well-known English general consumer review and rating site – Every member maintains a trust list which presents a user network of trust relationships – We crawled 51, 670 users who have rated a total of 83, 509 different items. The total number of ratings is 631, 064 – The total number of issued trust statements is 511, 799 15
Metrics • MAE and RMSE 16
Performance Comparison 17
Impact of Parameter beta 18
Impact of Similarity Functions 19
Conclusions • We proposed two new social recommendation methods • Our approaches perform better than other traditional and trust-aware recommendation methods • The methods scale well since the employed algorithm is linear with the observation of ratings 20
Future Work • Employ more accurate similarity functions • Consider item side regularization • Apply similar techniques to other social applications, like social search problems 21
Question I • What are the model assumptions? – Objective = Model Loss + Graph Smoothing – Graph quality is important, informally: • Contain “model-orthogonal” information • Graph structure: well-poor, poor-poor • Link weights reflect real similarity with relatively small variance – Graph constructed by social relation with VSS and PCC 22
Question I • What are the model assumptions? Then what role does social graph play here? – Social graph is not a similarity graph! Hao Ma, On Measuring Social Friend Interest Similarities in Recommender Systems. SIGIR 2014. 23
Question II • How different are average-based and individual-based regularization? Average-based Individual-based – If user i’s neighbors are fixed, take gradient w. r. t. U_i, two methods yield to the same optimum: 24
Question II • How different are average-based and individual-based regularization? – In the paper, the authors claimed for averagebased regularization: – Are these differences really exist between two regularization methods? 25
Question III • Global bias issue effect. – PMF assumes zero mean – Without bias, “zero mean” is not valid – Not presented in paper anywhere I can find it. 26
Thanks!
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