Flexible Interoperability in a Federated Digital Library of Theses and Dissertations

Federated digital libraries are composed of autonomous, possibly heterogeneous information services distributed across the Internet. Federation provides users with a seamless, integrated view of the collected information. We are creating a federated system for the Networked Digital Library of Theses and Dissertations (NDLTD), an international consortium of universities, libraries, and other supporting institutions focused on electronic theses and dissertations (ETDs). The NDLTD allows its members minimal restrictions and maximal autonomy, so federating requires dealing flexibly with differences among ontologies, data formats, and finding aids involving several thousand ETDs in four formats and two languages. Our solution involves adapting MARIAN, an object-oriented digital library system, to serve as mediation middleware for the federated NDLTD. Components of the solution include: 1) the use of several harvesting techniques; 2) an architecture based on object-oriented ontologies of searchers and metadata; 3) diversity within the harvested data joined to a single collection view for the user; and 4) an integrated framework for addressing such issues as data quality, information compression, and flexible search. The system can handle very large dynamic collections. It can add new sites and adapt to changes in existing sites. MARIAN’s modular architecture and powerful and flexible data model work together to build an effective integrated solution within a simple uniform framework.