An empirical study of methods for representing reusable software components is described. Thirty-five subjects searched for reusable components in a database of UNIX tools using four different representation methods: attribute-value, enumerated, faceted, and keyword. The study used Proteus, a reuse library system that supports multiple representation methods. Searching effectiveness was measured with recall, precision, and overlap. Search time for the four methods was also compared. Subjects rated the methods in terms of preference and helpfulness in understanding components. Some principles for constructing reuse libraries, based on the results of this study, are discussed.