Collections of already developed programs are important resources for efficient development of reliable software systems. In this paper, we propose a novel graph-representation model of a software component library (repository), called component rank model. This is based on analyzing actual usage relations of the components and propagating the significance through the usage relations. Using the component rank model, we have developed a Java class retrieval system named SPARS-J and applied SPARS-J to various collections of Java files. The result shows that SPARS-J gives a higher rank to components that are used more frequently. As a result, software engineers looking for a component have a better chance of finding it quickly. SPARS-J has been used by two companies, and has produced promising results.