  Harvested metadata often suffers from uneven quality to the point that
utility is compromised. Although some aggregators have developed methods for
evaluating and repairing specific metadata problems, it has been unclear how
these methods might be scaled into services that can be used within an
automated production environment. The National Science Digital Library (NSDL),
as part of its work with INFOMINE, has developed a model of ser-vice
interaction that enables loosely-coupled third party services to provide
metadata enhancements to a central repository, with interactions orchestrated
by a centralized software application.
