In the previous section we focused on the data utilized and generated in the recommendation process. In this section we provide an overview of the specific processes used in actual E-commerce recommender systems. We should point out that individual systems may actually use a combination of these processes. Each category discussed here represents a family of algorithms and approaches. It is beyond the scope of this work to survey the variant implementations of each process. Breese et al. (1998) compare a variety of algorithms for recommendation generation, and Herlocker et al. (1999) provide a detailed comparison of customer-to-customer correlation algorithms.