With the rise of the Internet, recommender systems are becoming a used solution to solve the information overload problem. These systems are like any other system, subject to noise: malicious noise that is caused by attacks and natural noise that is due to the human error. Many detection algorithms solve the noise problem. However, since natural noise and serendipity overlap in their definition, removing noise results in removing serendipity. Serendipity that is the happy surprise of finding something relevant unexpectedly is important for the issue of over personalization caused by the recommender ...