We propose an architecture for Digital Library Repositories that assures
long-term archival storage of digital objects.  The architecture is formed
by a federation of independent but collaborating sites, each managing a
collection of digital objects.  The architecture is based on the following
key components: use of signatures as object handles, no deletions of
digital objects, functional layering of services, the presence of an
awareness service in all layers, and use of disposable auxiliary
structures.  Long-term persistence of digital objects is achieved by
creating replicas at several sites.