Since the traditional Collaborative Filtering(CF)algorithm often leads to bad recommendation when users interests are changed,and inspired by the forgetting law of psychology,a non-lineal gradual forgetting collaborative filtering algorithm is developed which diminishes the importance of each rate with time and then determines similarities between different users.

Proposed in this paper is a wavelet-based hierarchical amnesic synopsis (W-HAS),which includes the amnesic feature of data stream in the generation of wavelet synopses.