The report summarizes work done in the study of measures for the effectiveness of the performance of large file systems. It consists of six sections: An "Introduction and Summary" which describes the background for the study, the approach taken in it, and summarizes the results; A discussion of the "Forms of Input", which characterizes the basic issues in representing complex phenomena in a form to be processed; An analysis of the lattice model of vocabulary structure and development of methodologies for vocabulary decomposition as a means of organizing formal representations; A characterization of the probabilities of file items in response to requests; The definition of a measure of file performance with emphasis on its relation to file organization in an environment of error and uncertainty; The presentation of a simulation by which the performance of large files can be exhibited and explored under different conditions. (Author)