Reseach Review Abstract With the exponential explosion of information growth, as one of the recommender system techniques, collaborative filtering becomes a powerful active technique to utilize data in information overload scene. This review first introduces the collaborative filtering and its key disadvantages, then describes and compares two kinds of collaborative filtering: Memory-based approach and Model-based approach. Then we take a look at the evaluation metrics and prevalent dataset of collaborative filtering. Finally we discuss the future challenges of collaborative filtering.

Reference Letter help~ At the request of Miss Li Dianshan, my student in the Department of Artistic Design, Beijing Forestry University, I am glad to write this letter furnishing my evaluation of her academic aptitude for your reference. Msiss Li Dianshan was admitted into Decoration major in 2008. I taught her calligraphy, and I was also her supervisor in the nature sketch and nature photography program. She was devoted to the arts she was studying with independent artistic views. In addition, she has an enthusiastic, opening attitude to study and realize. I believe her intense interest in arts is an essential asset for her further study. Miss Li Dianshan pays attention to her own experience and is keen on new things. When we went outside to sketch from nature, she would always like to learn the local culture and history from different regions, and the refining of these experiences were helpful in details for her later works. She is also good at extending her art horizons and works. For example, she applied a style of calligraphy from Stele of ZhangQian of the Han dynasty, which she once copied before, into other font designs and book designs. What particularly intrigued me more was her various attempts in artistic domain. During the nature photography activities， she spent much time developing films in the darkroom in order to try to get different effects. We communicated a lot and she valued my feedbacks, finally she produced some successful works. However, I should point out her painting skills and practical ability played a bigger role in her rapid promotion of artistic accomplishment. As far as I know, Miss Li Dianshan wishes to continue her study in the field of artistic design for an advanced degree. I am sure she has had sufficient prerequisite artistic culture for the subject and certainly has the ability to undertake the study. I recommend Ms. Li Dianshan without reservation and shall appreciate your favorable consideration of her application.