1. A method of setting up a DLSI space-based classifier for document classification comprising the steps of: preprocessing documents to distinguish terms of a word and a noun phrase from stop words; constructing system terms by setting up a term list as well as global weights; normalizing document vectors of collected documents, as well as centroid vectors of each cluster; constructing a differential term by intra-document matrix D I m×n I, such that each column in said matrix is a differential intra-document vector; decomposing the differential term by intra-document matrix D I, by an SVD algorithm, into D I &equals;U I S I V I T (S I &equals;diag(&dgr; I,1,&dgr; I,2,... )), followed by a composition of D I,k I &equals;U k I S k I V k I T giving an approximate D I in terms of an appropriate k I ; setting up a likelihood function of intra-differential document vector; constructing a term by extra-document matrix D E m×n E, such that each column of said extra-document matrix is an extra-differential document vector; decomposing D E, by exploiting the SVD algorithm, into D E &equals;U E S E V E T (S E &equals;diag(&dgr; E,1,&dgr; E,2,... )), then with a proper k E, defining D E,k E &equals;U k E S k E V k E T to approximate D E ; setting up a likelihood function of extra-differential document vector; setting up a posteriori function; and using the DLSI space-based classifier to automatically classify a document.