  We describe the underlying data model and implementation of a new
architecture for the National Science Digital Library (NSDL) by the Core
Integration Team (CI). The architecture is based on the notion of an
information network overlay. This network, implemented as a graph of digital
objects in a Fedora repository, allows the representation of multiple
information entities and their relationships. The architecture provides the
framework for contextualization and reuse of resources, which we argue is
essential for the utility of the NSDL as a tool for teaching and learning.
