AbstractIn a bibliographic information system the database consists of a set of document representatives. Part of each document representative is a list of index terms whose function is to identify the content of the document represented. These index terms can be derived using an automated process. It is argued that automatic methods do not result in the best set of index terms being assigned to a document representative. A mathematical model is proposed which describes an information system which includes a method, document learning, of improving the set of index terms assigned to a document representative.