The simplest types of recommendations, from a technical and algorithmic perspective, are the non-personalized ones. That is, they are not customized to take into account specific user preferences. Such recommendations can include best-selling products, various top 10 songs, blockbuster movies, or the most downloaded apps of the week.
Non-personalized recommendations are less challenging technically, but also considerably less powerful. They can be good approximations in certain cases, especially when the product catalog is not very large (there are not that many Hollywood releases, for example). But for an e-commerce retailer like Amazon, with millions of products ...
