recommendationsystem-140410131156-phpapp01 (1).pdf
- 1. Recommendation Systems Dept. of Comp. Engg.
- 2. What is a Recommmendation System? Recommendation system is an information filtering technique, which provides users with information, which he/she may be interested in. Examples:
- 3. Areas of Use
- 4. Why there is a need? “Getting Information off the internet is like taking a drink from a fire hydrant” - Mitchell Kapor - Information Overload - User Experience - Revenues Recommender systems help in addressing the information overload problem by retrieving the information desired by the user based on his or similar users' preferences and interests.
- 5. Types of Recommendation System In General, two types of recommender system. 1. Personalized
- 7. Types... cont'd - Personalized - Non-Personalized
- 8. Techniques : Data Acquisition 1. Explicit Data - Customer Ratings - Feedback - Demographics - Physiographics - Ephemeral Needs 2. Implicit Data - Purchase History - Click or Browse History 3. Product Information - Product Taxonomy - Product Attributes - Product Descriptions
- 9. Techniques : Recommendation Generation 1. Collaborative Filtering method finds a subset of users who have similar tastes and preferences to the target user and use this subset for offering recommendations. Basic Assumptions : - Users with similar interests have common preferences. - Sufficiently large number of user preferences are available. Main Approaches : - User Based - Item Based
- 10. Techniques : Recommendation Generation User-Based Collaborative Filtering ● Use user-item rating matrix ● Make user-to-user correlations ● Find highly correlated users ● Recommend items preferred by those users Pearson Correlation : Prediction Function :
- 11. Techniques : Recommendation Generation User Based Collaborative Filtering Item User I1 I2 I3 I4 I5 U1 5 8 7 8 U2 10 1 U3 2 2 10 9 9 U4 2 9 9 10 U5 1 5 1 User a 2 9 10 Recommend items preferred by highly correlated user U3 I5
- 12. Techniques : Recommendation Generation User Based Collaborative Filtering ● Advantage : - No knowledge about item features needed ● Problems : - New user cold start problem - New item cold start problem: items with few rating cannot easily be recommended - Sparsity problem: If there are many items to be recommended, user/rating matrix is sparse and it hard to find the users who have rated the same item. - Popularity Bias: Tend to recommend only popular items. e.g. RINGO, GroupLens
- 13. Techniques : Recommendation Generation Item Based Collaborative Filtering ● Use user-item ratings matrix ● Make item-to-item correlations ● Find items that are highly correlated ● Recommend items with highest correlation Similarity Metric : Prediction Function :
- 14. Techniques : Recommendation Generation Item Based Collaborative Filtering Item User I1 I2 I3 Item I I5 U1 5 8 7 8 U2 10 1 U3 2 10 9 9 U4 2 9 9 10 U5 1 5 1 User a 2 9 10 Recommend items highly correlated to preferred items I5
- 15. Techniques : Recommendation Generation Item Based Collaborative Filtering ● Advantages : - No knowledge about item features needed - Better scalability, because correlations between limited number of items instead of very large number of users - Reduced sparsity problem ● Problems : - New user cold start problem - New item cold start problem e.g. Amazon, eBay
- 16. Techniques : Recommendation Generation 2. Content Based Systems recommend items similar to those a user has liked (browsed/purchased) in the past. OR Recommendations are based on the content of items rather on other user's opinion. User Profiles: Create user profiles to describe the types of items that user prefers. e.g. User1 likes sci-fi, action and comedy. Recommendation on the basis of keywords are also classified under content based. e.g. Letizia e.g. IMDB, Last.fm(scrobbler)
- 17. Techniques : Recommendation Generation Content Based Systems Cont'd... Advantages: - No need for data on other users. No cold start and sparsity. - Able to recommend users with unique taste. - Able to recommend new and unpopular items. - Can provide explanation for recommendation. Limitations: - Data should be in structured format. - Unable to use quality judgements from other users.
- 18. Case Study 1. Amazon 2. YouTube
- 19. Amazon's Demand and Solution Demand : ● Amazon had more than 29 million customers and several million catalog items. ● Amazon use recommendation algorithms to personalize the online store for each customer in real time. Solution : ● Existing algorithm were evaluated over small data sets. ● Reduce M by randomly sampling the customers or discarding customers with few purchases. (M : the number of customers) ● Reduce N by discarding very popular or unpopular items. (N : the number of items) ● Dimensionality reduction techniques such as clustering.
- 20. The Amazon Item-to-Item Collaborative Filtering Algorithm Algorithm : For each item in product catalog, I1 For each customer C who purchased I1 For each item I2 purchased by customer C Record that a customer purchased I1 and I2 For each item I2 Compute the similarity between I1 and I2 Algorithm Complexity : ● Worst Case : O(N2M) ● In practice : O(NM), 'cause customers have fewer purchases.
- 23. YouTube Recommendation System Generating Recommendation Candidates