Recommendations are suggestions to someone about things that might be interesting to him. For example, you would recommend a good book to a friend who you know has similar interests as you. We often find use cases for recommendations in online retail. For example, when you browse a product, Amazon suggests other products also bought by users who bought that particular item.

An online retail site such as Amazon has a very large collection of items. Although books are found under several categories, often each category has too many to browse one after the other. Recommendations make the user's life easier by helping him find the best product for his tastes, and at the same time increase sales.

There are many ways to make recommendations: