MONO91 Indexes Compiled by Machine chapter Mary Elizabeth Stevens National Bureau of Standards which may also have numeric codes; and a set of indexing tables. These tables contain item numbers in the leftmost column3 and either the names or the codes for indexing terms assigned to an item along the row. There is one such table for each distinct term used in indexing the items. To facilitate searching, only those terms which are of higher numeric or alphabetic order than that for the term for which the particular table is compiled are recorded in the rows. Thus to make a search on several terms, the user turns to the table for the one of these terms that has the lowest term value, which table records all items to which the term has been assigned, and checks the rows of the table for the second lowest ranking term, the third, and so on. Variations in the Tabledex method allow for the automatic assignment of numeric codes to the indexing terms based on relative frequency of use within the collection. Ledley also discusses methods for finding articles associated with all except one, all except two, or all except n of the given words in a search prescription. 1/ A first example of a computer-compiled Tabledex index was that to a bibliography prepared by the Library of Congress for the International Geophysical Year (Zusman et al, 1962 [661]). [OCRerr]" The computer program for the IBM 7090 carried out the operations of assigning accession numbers, extracting index terms and compiling the term lists, determining frequencies so as to assign frequency numbers to the terms, organizing and preparing the tables, and developing an author index. Two formats were used, one giving terms by numeric code and the other spelling out the terms as normal words. The latter feature provides a measure of browsability in the system. Y/ A Tabledex compilation program is also in use at the Applied Physics Laboratory of Johns Hopkins University (Olmer and Rich, 1963 [454]). Another coordinate index search tool, making use of what is in effect a document- descriptor matrix with special codes and column arrangements to save space and facilitate rapid scanning, is the Scan-Column Index suggested in 1960by OtConnor [449]. He further suggested the use of computers for compilation, as follows: IA computer can organize information about documents into a scan-column index. The input needed consists of the document identifications and their accompanying 1/ 2/ 3/ Ledley, [OCRerr]959 [352], pp. 1235-1239. See also National Science Foundation CR&D No.11 [430], pp. 130-131. Zusman, et al 1962, [661], p. ii: ... The word tables have the advantage that browsing can be accomplished and possible associations made during the search... Such `browsing1 can be enhanced by including at the end of each row in a table all II the other words also associated with the article of that row 26