INFORMATION RETRIEVAL”Information retrieval in the present sense now meanstwo things. One, document retrieval, uses standardizedindexing techniques to draw desired classes of unit docu-ments from a central pool. The other, content retrieval,holds a body of integrated knowledge to which the usermay address questions. (For a unified treatment of the twotypes, see Licklider.1) Each is important.

ar on the right of the screen.