The SCORM (Sharable Content Object Reference Model) specification defines metadata of learning objects, which are used as the elementary reusable components in distance learning. The CORDRA (Content Object Repository Discovery and Registration/Resolution Architecture) specification provides a common architecture for the resolution, discovery, and sharing of these learning objects. They define standardized ways in which learning objects can be discovered and reused by content designers. However, the current CORDRA and the definition of objects in SCORM only allow an object to be copied, updated, and re-organized in a new content aggregation, which is used as a delivery package to end users. This paper proposes a revised CORDRA architecture and a reusability mechanism to make instruction design easier. We propose a structure called a reusability tree for tracking the history of reuse of learning objects in CORDRA. This paper also defines the notions of similarity and diversity of learning objects to make easier for users to precisely search for reusable learning objects, with additional meaningful information to support instruction designs.