A digital library is a managed collection of digital objects and services that support the storage, discovery, retrieval, and preservation of those objects. We describe an open architecture in which core digital library functionality is partitioned into a set of well-defined services. Each service can be accessed through a set of service requests that define its public interface. This paper describes a general digital object model and a set of service components, which include a naming service, a repository service, an index service, and a collection service. Interoperability is promoted when digital libraries are assembled from this set of core service components.