Many different approaches have been applied to the basic problem of making accurate and efficient recommender and data mining systems. Many of the technologies used in the actual recommender systems studied are fairly simple database queries. Automatic recommender systems, however, use a wide range of techniques, ranging from nearest neighbor algorithms to Bayesian analysis. The worst-case performance of many of these algorithms is known to be poor. However, many of the algorithms have been tuned to use heuristics that are particularly efficient on the types of data that occur in practice.