1. A system for generating a set of parameters for use in determining whether a given document belongs to a specified one of a plurality of predetermined categories, the system comprising: a set of documents, each document having an identifier (ID); a document data set containing a record for each document which record contains a document ID of said document and a feature vector representing features of said document in a predefined vector space; a category data set containing a record for each category which record contains a category ID of said category, a category name and said set of parameters, said parameters including a reference vector representing features of said category in said predefined vector space and a threshold value for said category; means for calculating, for each document (or the document), a membership score indicative of whether the document belongs to said specified category by using said feature vector of the document, and said reference vector and said threshold value associated with said specified category; means for supporting an operator to input various command parameters for selecting documents for which the calculated membership scores are to be evaluated; means, responsive to an input of one of said command parameters, for visually presenting information useful for said selection of documents to said operator; evaluation means for displaying selected documents and permitting said operator to evaluate (i.e., set an evaluated membership score as) said membership score of each of the displayed selected documents; means for storing said evaluated membership score, if exists, of each document for each of said predetermined categories; and means for updating said reference vector of said specified category by using said evaluated membership score, if exists, of each document in said storing means, said calculated membership scores of documents having not been evaluated for said specified category and feature vectors contained in said document data set.