Some issues related to AL have already been well studied in Statistics; this is
not the case in Computer Science, where research is still wanting. Recommender
Systems are changing at a rapid pace and becoming more and more complex. An
example of this is the system that won the NetFlix Recommendation Challenge,
which combined multiple predictive methods in an ensemble manner (see Chapter
5). Given the high rate of change in predictive methods of RSs, and their complex
interaction with AL, there is an ever increasing need for new approaches.