In this chapter, we added free-text search, and also added recommendations based on the collaborative filtering model we learned about. We also discussed how complex it is to understand the behavior of recommender systems. In the next chapter, we will discuss a case study of a real-world, Scala based open source machine learning server called PredictionIO. It covers most of the steps we discussed for setting up data ingestion and a processing pipeline. We will also discuss a hybrid recommender called unified recommender.