ISR11 An Experimental Investigation of Automatic Hierarchy Generation chapter G. Blomgren A. Goodman L. Kelly Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. viii-8 thesaurus structure, is desired. This results in a potential benefit to the system user, because composite hierarchies in v[OCRerr]rying degrees of detail can be made available to him. The degree of detail is a function of the chosen range R and can be characterized by a number (say between 1 and 10). To obtain a particular hierarchy for modifying his queries, the user merely specifies one of the numbers; the corresponding hierarchy is then made available to him. A continu[OCRerr]ion of the above example illustrates the construction and the use of composite hierarchies. First, the relations bet.7een peirs of terms are determined as K varies. This may be done in two ways: a) A set of hierarchies for various values of K between 0 and 1 is constructed, as illustrated by the graphs on page 6. b) The relations between each pair of concepts are examined as K varies from 0 to 1. Second, 1trange tablestt arc constructed; these display the relation- ships found and their `tduration [OCRerr][OCRerr]g[OCRerr]5V (ranges of K-values for which they exist) This is done conveniently if K is varied in uniform increments. The example yields the table sho[OCRerr][OCRerr] on the next page; K is incremented by 0.05. For the example the lower bound occurs between 0.20 and 0.25; the upper bound occurs between 0.85 and 0.90; thus K is varied from 0.20 to 0.90. The range lengths provide a convenient means of assigning numbers to the various composite hierarchies. In this particular example the numbers are merely the range lengths. Composite hierarchies for numbers (range lengths) 9, 5, [OCRerr], and 3 are presented.