Design equations for retrieval systems based on the swets model

Swets's theory of information retrieval allows the threads of document weighting formulae, probabilistic measures of effectiveness, and management theory to be woven into a coherent pattern. Benefits of the theory are the beginnings of a quantitative description of retrieval languages, a clear distinction between retrieval `systems' and `language', a recognition that retrieval performance can be tailored to suit individual needs in a systematic way, and confirmation that question Generality is a pivotal feature of the retrieval process. The hypotheses involved are still in need of rigorous experimental testing.