ISR10 Introduction chapter Joseph John Rocchio Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. 1-3 a) the representation 0£ the information content 0£ source documents, i.e. the indexing function; b) the representation 0£ the information needs 0£ the users 0£ the system, i.e. the search request forunilation function; c) the matching operation between search request representations and source document representations, i.e. the search or retrieval functio[OCRerr]. in addition to this functional characterization, other elements 0£ document retrieval system organization are important in an: operational framework. Such characteristics as storage organization, input-output facilities, document acquisition policy, economic fact6rs and others may be critical in an operational sense9, but for £he purposes 0£ this report these will be considered primarily as secondary factors. In this sense, then, the main purpose here is to consider the logical and methodological aspects of the mechanization of document retrieval systems, and in so doing to i[OCRerr]ore ma[OCRerr] 0£ the operational factors which may be important in other contexts. The true information content of a document or se[OCRerr]ent of natural langnage text might be defined as existing only in the mind of its author. The representation of this content in recorded form via the natural langua[OCRerr]e can be considered as an attempt at communication. That in fact such co'nm'1nication is successful on the average might in part be measured in terms of human progress. In any case, the information content of a document is a theoretically tenuous concept.