1. An information retrieval system for retrieving documents added to a database with respect to time, said documents being converted into document-attribute matrix and stored within said information retrieval system, and said document-attribute matrix being constituted by document-attribute submatrices added in order with respect to time, said information retrieval system comprising: means for generating and storing a predetermined type matrix from said document-attribute matrix, means for generating said document-attribute submatrix from documents being added to said database during a specific time period, means for updating said predetermined type matrix using knowledge with respect to said document-attribute submatrix and for executing singular value decomposition on updated said predetermined type matrix to execute dimension reduction of all document-attribute matrices stored within said database, and means for retrieving information with respect to a user input query using said dimension reduced document-attribute matrix.