In the BlueView project, digital library services are developed and partially implemented based on the architecture of virtual document servers. Using standard tools like fulltext database or information retrieval systems, objectrelational database management systems, and replication and caching services, different heterogeneous local document servers have been integrated into one virtual server. Access to heterogeneous local systems can now be performed via a single query interface, integrating features of database query systems and information retrieval or search services. The BlueView distributed query processing allows for combining structured queries against metadata with content-based (text retrieval) queries against fulltext collections. Legacy systems like existing preprint servers, search engines, or metadata (catalog) systems can be integrated as well. Metadata and fulltext documents can be replicated within this distributed architecture. In particular, in the view of member...