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Recommender systems at the long tail

Recommender systems form the core of e-commerce systems. In this paper we take a top-down view of recommender systems and identify challenges, opportunities, and approaches in building recommender systems for a marketplace platform. We use eBay as an example where the elaborate interaction offers a number opportunities for creative recommendations. However, eBay also poses complexities resulting from high sparsity of relationships. Our discussion can be generalized beyond eBay to other marketplaces.