An ontology-based knowledge repository, similar to the common digital archives for libraries, has been built to support collaborative on-line learning. A notable difference in the repository is that a resource in the depository needs not have a physical presence. Features in resource categorization and ratings provide opportunities for reflective thinking on a particular resource in the repository and its relevancy to the study domain. This paper describes the motivation, design theories and components of the repository system. An initial assessment of the system in actual use in a large class is obtained and the result is discussed.