Ronny lempelyahooindiabigthinkerapril2013

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Recommendation Challenges in Web Media Settings Ronny Lempel Yahoo! Labs, Haifa, Israel
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Transcript of Ronny lempelyahooindiabigthinkerapril2013

  • 1.RecommendationChallenges in Web MediaSettings Ronny Lempel Yahoo! Labs, Haifa, Israel

2. Recommender Systems Pioneered in the mid/late 90s by Amazon Today applied everywhere Shopping sites Content sites (news, sports, gossip, ) Multimedia streaming services (videos, music) Social networks Easily merit a dedicated academic course-1- Bangalore/MumbaiConfidential Yahoo! 2013 3. Recommendation in Social Networks-2- Bangalore/MumbaiConfidential Yahoo! 2013 4. Recommender Systems Example of Effectiveness 1988: Random House releasesTouching the Void, a book by amountain climber detailing a harrowingaccount of near death in the Andes It got good reviews but modest commercial success 1999: Into Thin Air, another mountain-climbing tragedybook, becomes a best-seller By virtue of Amazons recommender system, Touchingthe Void started to sell again, prompting Random Houseto rush out a new edition A revised paperback edition spent 14 weeks on the New York Times bestseller list From The Long Tail, by Chris Anderson -3- Bangalore/MumbaiConfidentialYahoo! 2013 5. The Netflix ChallengeSlides 4-6 courtesy ofYehuda Koren, memberof Challenge winnersBellkors PragmaticChaos -4- Bangalore/MumbaiConfidentialYahoo! 2013 6. Were quite curious, really. To the tune ofone million dollars. Netflix Prize rules Goal was to improve on Netflix existing movierecommendation technology The open-to-the-public contest began October 2, 2006;winners announced September 2009 Prize Based on reduction in root mean squared error (RMSE) on test data $1 million grand prize for 10% improvement on Cinematch result $50K 2007 progress prize for 8.43% improvement $50K 2008 progress prize for 9.44% improvement Netflix gets full rights to use IP developed by the winners Example of Crowdsourcing Netflix basically got over 100 researcher years (and good publicity) for $1.1M-5-Bangalore/MumbaiConfidentialYahoo! 2013 7. Netflix Movie Ratings Data Training data Test data Training data user movie score usermovie 100 million 1 211 162?ratings 12135 196? 480,000 users 23454 27 ? 17,770 movies 6 years of data:21234 23 ?2000-200527683 347? Test data3 765 315? Last few ratings4 454 441?of each user (2.855681 428?million) 53422 593? Dates of ratings are 52342 574?given 6 765 669? 6 564 683?-6-Bangalore/MumbaiConfidentialYahoo! 2013 8. Recommender Systems Mathematical Abstraction Consider a matrix R of users and the items theyve consumed Users correspond to the rows of R, products to its columns, withri,j=1 whenever person i consumed item j In other cases, ri,j might be the rating given by person i on item j The matrix R is typically very sparseItems and often very large Real-life task: top-k recommendation users From among the items that werent R=consumed by each user, predict whichones the user would most enjoy Related task on ratings data: matrix completion|U| x |I| Predict users ratings for items they haveyet to rate, i.e. complete missing values -7-Bangalore/MumbaiConfidential Yahoo! 2013 9. Types of Recommender Systems At a high level, two main techniques: Content-based recommendation: characterizes theaffinity of users to certain features (content, metadata)of their preferred items Lots of classification technology under the hood Collaborative Filtering: exploits similar consumption and preference patterns between users See next slides Many state of the art systems combine both techniques -8-Bangalore/MumbaiConfidential Yahoo! 2013 10. Collaborative Filtering Neighborhood Models Compute the similarity of items [users] to each other Items are considered similar when users tend to rate themsimilarly or to co-consume them Users are considered similar when they tend to co-consumeitems or rate items similarly Recommend to a user: Items similar to items he/she has already consumed [ratedhighly] Items consumed [rated highly] by similar users Key questions: How exactly to define pair-wise similarities? How to combine them into quality recommendations?-9- Bangalore/MumbaiConfidential Yahoo! 2013 11. Collaborative Filtering Matrix Factorization Latent factor models (LFM): Maps both users and items to some f-dimensional space Rf, i.e. produce f-dimensional vectors vu and wi for each user and items Define rating estimates as inner products: qij = Main problem: finding a mapping of users and items to the latent factor space that produces good estimates Closely related to dimensionality reduction techniques of the ratings matrix R (e.g. Singular Value Decomposition) ItemsVW usersR= |U| x |I| |U| x ff x |I| - 10 - Bangalore/MumbaiConfidential Yahoo! 2013 12. Web Media Sites- 11 - Bangalore/MumbaiConfidentialYahoo! 2013 13. Challenge: Cold Start Problems Good recommendations require observed data on the userbeing recommended to [the items being recommended] What did the user consume/enjoy before? Which users consumed/enjoyed this item before? User cold start: what happens when a new user arrives to asystem? How can the system make a good first impression? Item cold start: how do we recommend newly arrived itemswith little historic consumption? In certain settings, items areephemeral a significant portion oftheir lifetime is spent in cold-start state E.g. news recommendation - 12 - Bangalore/MumbaiConfidential Yahoo! 2013 14. Low False-Positive CostsFalse positive: recommending an irrelevant item Consequence, in media sites: a bit of lost time As opposed to lots of lost time or money in other settings Opportunity: better address cold-start issues Item cold-start: show new item to select group of userswhose feedback should help in modeling it to everyone Note the very short item life times in news cycles User cold-start: more aggressive exploration Vs. playing it safe and perpetuating popular items Search: injecting randomization into the ranking of searchresults (Pandey et al., VLDB 2005)- 13 - Bangalore/MumbaiConfidentialYahoo! 2013 15. Challenge: Inferring Negative Feedback In many recommendation settings we only know whichitems users have consumed, not whether they liked them I.e. no explicit ratings data What can we infer about satisfaction of consumed itemsfrom observing other interactions with the content? Web pages: what happens after the initial click? Short online videos: what happens after pressing play? TV programs: zapping patterns What can we infer about items the user did not consume? Was the user even aware of the items he/she did notconsume? What items did the recommender system expose the user to? - 14 -Bangalore/MumbaiConfidentialYahoo! 2013 16. Presentation Bias Effect on Media Consumption Pop Culture: items longevity creates familiarity Media sites: items are ephemeral, and users are mostlyunaware of items the site did not expose them to Presentation bias obscures users true taste theyessentially select the best of the little that was shown Must correctly account for presentation bias whenmodeling: seen and not selected not seen and notselected Search: negative interpretation of skipped search results(Joachims, KDD2002)- 15 - Bangalore/MumbaiConfidentialYahoo! 2013 17. Layouts of Recommendation Modules Interpreting interactions in vertical layouts is easy usingthe skips paradigm What about 2D, tabbed, horizontal layouts? - 16 - Bangalore/MumbaiConfidential Yahoo! 2013 18. Layouts of Recommendation Modules What about multiplepresentation formats? - 17 - Bangalore/MumbaiConfidential Yahoo! 2013 19. PersonalizedPopularContextual - 18 - Bangalore/MumbaiConfidential Yahoo! 2013 20. Contextualized, Personalization, Popular Web media sites often display links to additional stories on each article page Matching the articles context, matching the user, consumed bythe users friends, popular When creating a unified list for a given a user reading a specific page, what should be the relative importance of matching the additional stories to the page vs. matching to the user? Ignoring story context might create offending recommendations Related direction: Tensor Factorization, Karatzoglou et. al, RecSys2010- 19 - Bangalore/MumbaiConfidentialYahoo! 2013 21. Challenge: Incremental Collaborative Filtering In a live system, we often cannot afford to recomputerecommendations regularly over the entire history Problem: neither neighborhood models nor matrixfactorization models easily lend themselves to faithfulincremental processing User-ItemUser-ItemUser-ItemMi = CF-ALG(ti)Interactions Interactions Interactions t1 t2 t3f, f { M1, M2 } CF_ALG(t1t2) T Is there a model aggregation function f(Mprev, Mcurr) that isgood enough? - 20 - Bangalore/MumbaiConfidential Yahoo! 2013 22. Challenge: Repeated Recommendations One typically doesnt buy the same book twice, nor dopeople typically read the same news story twice But people listen to the songs they like over and overagain, and watch movies they like multiple times as well When and how frequently is it ok to recommend an itemthat was already consumed? On the other hand, when should we stop showing arecommendation if the user doesnt act upon it? Implication: a recommendation system may not only needto track aggregated consumption to-date, It may need to track consumption timelines It may need to track recommendation history- 21 - Bangalore/MumbaiConfidentialYahoo! 2013 23. Challenge: Recommending Sets & Sequences ofItems In some domains, users consume multiple items in rapidsuccession (e.g. music playlists) Recent works: WWW2012 (Aizenberg et al., sets) and KDD2012 (Chen et al., sequences) From Independent utility of recommendations to set orsequence utility, predicting items that go well together Sometimes need to respect constraints Tiling recommendations: in TV Watchlist generation, thebroadcast schedules further complicates matters due toprogram overlaps Perhaps a new domain of constrained recommendations? Search: result set attributes (e.g. diversity) in Search(Agrawal et al., WSDM2009) Netflix tutorial at RecSys2012: diversity is key @Netflix- 22 - Bangalore/MumbaiConfidentialYahoo! 2013 24. Social Networks and RecommendationComputation Some are hailing social networks as asilver bullet for recommender systems Tell me who your friends are and well tell you what you like Is it really the case that we like thesame media as our friends? Affinity trumps friendship! There are people out there who are more like us than our limited set of friends Once affinity is considered, the marginal value of social connections is often negligible Not to be confused with non-friendship social networks,where connections are affinity related (Epinions)- 23 - Bangalore/MumbaiConfidentialYahoo! 2013 RecSys 202 25. Social Networks and RecommendationConsumption Previous slide nonewithstanding, social is a greatmotivator for consuming recommendations People like you rate Lincoln very highly vs. Your friends Alice and Bob saw Lincoln last night and loved it Explaining recommendations for motivating and increasingconsumption is an emerging practice Some commercial systems completely separate theirexplanation generation from their recommendation generation So Alice and Bob may not be why the system recommended Lincoln to you, but they will be leveraged to get you to watch it Privacy in the face of joint consumption of a personalizedexperience? - 24 -Bangalore/MumbaiConfidentialYahoo! 2013 RecSys 202 26. Questions, Comments?Thank you!rlempel (at) yahoo-inc dot com - 25 -Yahoo! Confidential