MONO91 Indexes Compiled by Machine chapter Mary Elizabeth Stevens National Bureau of Standards index terms... and an indication of either the number of columns desired or the column density desired. The computer will determine the frequency of each term, the positive and negative correlations of terms, and the quantity of these correlations by counting or sampling key figures, such as the average number of terms per document. It then can assign column-character codes accordingly. - In 1961, Costello described the use of computer techniques for compilation and computer printout of a dual dictionary for a coordinate indexing system using links and roles at DuPont's Polychemicals Department. Mter manual analysis, term-role assign- ments are keypunched, the cards are listed for editing including the elimination of synonyms and the indication of appropriate postings to more generic terms, and re- keypunched for conversion to magnetic tape. Tapes for posting of items and links to term-roles are merged by computer with tapes giving alphabetical equivalents of term codes and with appropriate syndetic indications for final output on an IBM 407 high-speed printer [141]. Still another instance of a coordinate index, modified to show pre-coordination of terms as compiled by computer, is that ot the Electronic Properties Information Center (Johnson, 1963 [301]). The system consists of abstract cards maintained in accession number order, together with machine printouts that pre-coordinate descriptors within nine major categories. The listings of pre-coordinated descriptors are arranged in three different indexes; alphabetically arranged within each category, alphabetized with- out respect to category but with code indication of the category reference, and a non- categorized listing arranged alphabetically in reverse order. Advantages of machine processing include the ease with which various statistical counts can be made, such as the average number of items in the system for a given material and a specified property. Summary indications of the state-of-the-art in the field of interest can be obtained, "for the system will indicate not only areas where research has been done, but also areas where gaps in the literature occur, and a measure of the growth of research activities in the field can be developed." [OCRerr]2I Z. 4 Citation Indexes "A citation index is a directory of cited references in which each reference is accompanied by a list of source documents which cite it." This is a relatively new 1/ 2/ 3/ O'Connor, 1962 [449], pp 18-49. Johnson, 1963 [301], p. 296. Sher and Garfield, 1963 [546], p. 63. 27