ISR11 The SMART System -- Retrieval Results and Future Plans chapter G. Salton Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. `-5 6) Deep indexing procedures which supply new information identifiers of which some are useful but many are not usually improve recall but depress precision. 7) Statistical concept-concept associations can be used to improve recall performance particularly for collections for which a well ordered synonym dictionary does not exist. 8) Keyword matching systems based on manually assigned index terms are found (at least for one well-known document collection in aerodynamics) to be not substantially superior to raw word matching techniques, and to be actually inferior to statistical word associations and to thesaurus methods. 9) Iterative search techniques, based on feedback information supplied by the user as a result of.previous retrieval procedures, appear to offer major promise for more effective search operations. If these results are accepted as generally valid, one must conclude that future information centers will probably not be based on manual subject indexing, but will make use of some form of automatic text analysis. Axrlong the techniques likely to be implemented in practice are synonym recognition and phrase generation methods made possible by the construction of suitable thesauruses and phrase dictionaries, and statistical term-term association procedures. Document identifiers may be expected to be based on document abstracts, or longer document excerpts, and weights will be assigned to improve retrieval performance. A variety of additional techniques, including hierarchical subjectexpansions and aut[OCRerr]natic syntactic analyses maybe used under special circumstances, but their general applicability is still unproved. 3. Discussion and Future Plans In discussing the evaluation results previously outlined, it is important