ISR11 Design Consideration for Time Shared Automatic Documentation Centers chapter M. E. Lesk Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. x-8 a request which can be answered correctly. The computer is a better judge of its own flaws and requirements than a user who has not seen the system before. It may be expected, then, that in case a) iterative retrieval based upon feedback will be superior to rephrasing by any but the most experienced users. In cases b) and c), however, where parts of the question as stated are actually misleading and where more is required than simply adjusting the style of writing of the user, feedback may be expected to be less useful. In case c) clearly a complete rewriting of the question is called for. The computer might nevertheless assist in this rewriting by displaying, upon request, portions of the thesauri and/or hierarchy `in the region being studied. The above outline should be c[OCRerr]m[OCRerr]on to virtually all requests submitted to the retrieval system. Some additional features might be needed frequently. For example, a method of arbitrarily marking certain documents to prevent their retrieval will be necessary. The most obvious examples of this need arise in the case of a multi-lingual document collection where users will wish to specify the languages that they can read, or in the case of a partially classified collection in which users without the appropriate security clearance zinist be denied access to certain documents. Suen an exclusion feature can also be used positively, however. Users might wish to request only current documents, for example. Furthezi[OCRerr]ore, someone who is totally unfamiliar with a field might wish to begin by requesting only review articles and books. There may well be a demand by students for textbooks or other more elementary treatments of a subject. Another specialized facility that would often be used is a set of special-purpose dictionaries. In fields with rapidly changing vocabulary,