IRS13 Search Matching Functions chapter E. M. Keen Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. 111-6 search time frequently becomes a problem, requiring the batching of search requests for reasons of economy. One specific part of the search time problem reflects on the use of the logical relations in the search formulations, since complex logic may tend to increase search time. This problem is circumvented to some extent in the NASA search system by the use of term weights to get the same results as logical formulations, with reduced machine effort. [1] 3. A third problem relates to the cut-off, which is rarely critical in manual systems where a searcher/system interaction may control the search as it proceeds, but in mechanized systems the total search formulation IIrLiSt be made in advance of the search and no changes are normally possible during the search. This problem is again linked to the logical relations in the formulation, since too few documents will be retrieved if the search logic is made too restrictive and tt[OCRerr]g[OCRerr][OCRerr]I; contrariwise, if it is made too `looset more documents than the user is willing to examine may be retrieved. An example of this latter point is given using an actual search made in the Medlars system. The request statement and search formulation are shown in Figure 2, and the search of the total document file of nearly half a million items eventually produced eleven references. The user was asked, before the search was carried out to indicate the number of journal articles relevant to his request that he considered likely to have been published since January l96[OCRerr]; 6 - 20 was chosen as a likely range for the number of relevant items. It is surprising therefore that after receiving the 11 references retrieved in the search, the requestor did not seem to be satisfied, and the librarian who handled the request reports the requestor as saying, "In view of the small return ... Dr. X would be interested in any articles dealing with oxygen concentration in the cerebrospinal fluid." Clearly the system and the search formulation are not at fault in this case: it is just a case of a change in requestor need, presumably arising from the requestor's examination of some retrieved document. This changed need, in the Medlars system, requires a completely new search of the system.