Collaborative Filtering (CF) is a successful approach commonly used by many recommender systems
Conventional CF-based methods use the ratings given to items by users as the sole source of information for learning to make recommendation
However, the ratings are often very sparse in many applications, causing CF-based methods to degrade significantly in their recommendation performance
To address this Sparsity problem, auxiliary information such as item content information may be utilized
Collaborative topic regression (CTR) is an appealing recent method taking this approach which tightly couples the two components that learn from two different sources of information
Nevertheless, the latent representation learned by CTR may not be very effective when the auxiliary information is very sparse.
generalizing recent advances in deep learning from i.i.d input to non-i.i.d (CF-based) input and propose a hierarchical Bayesian model called collaborative deep learning (CDL), which jointly performs deep representation learning for the content information and collaborative Filtering for the ratings (feedback) matrix.