19.2.2 The Traditional Recommender Systems Paradigm
Recommender systems are software applications that aim at predicting the user interest for a particular resource based on a collection of user profiles, e.g., the user’s history of purchase/resources’ ratings, click-stream data, demographic information, and so forth. Usually RS predict ratings of resources or suggest a list of new resources that the user hopefully will like the most. Traditionally, for m users and n resources, the user profiles are represented in a sparse user-resource matrix X ? Rm?n ? {.}, where {.} denote missing values. The matrix can be decomposed into row vectors: