| 
         
          | As
              the market of electronic commerce grows explosively, it becomes
              more and more important to provide the recommendation system which
              suggests the pre- ferred items for consumers using the large-scale
              customers database. In this paper, we discuss the algorithms and
              their performances of the recommendation systems using the collaborative
              filtering in the case of the Netflix database: they are, 1) memory-based
              system (k-nearest neighbor using the correlation coefficients),
              2) model-based system (matrix decomposition), and 3) the combination
              method. When the customer-item matrix is a sparse matrix like the
              Netflix database, the matrix decomposition method shows better
              performance than the k-nearrest neighbor; in addition, it is found
              that the combination method of the two methods provide a much better
              performance. |   
          | 
 |   
          |  |  |  |   
          | 
               
                | Netflix, collaborative filtering, k-nearest
                    neighbor, matrix decomposition, singular-value decomposition,
                  combination method. |  |  |