The integrated and transparent access to heterogeneous information resources, stored in distributed digital library and repositories, autonomously managed by different institutions is an important challenge in the digital library research area. From this perspective, this work reviews the main problems to achieve interoperability between digital libraries: different technical solutions, levels of interoperability, federated system architecture, copyright issues and evaluation parameters of interoperability solutions. It analyses also how the new development in Information Technology and Semantic Web have been applied to improve interoperable digital library systems. As conclusions it discusses the main challenges facing present digital library research to implement the next generation of digital libraries.
interoperability; digital libraries; distributed systems; digital repositories federation; digital rights management (DRM)