In a SPARC position paper (http://www.arl.org/sparc/IR/ir.html) published in 2002 Raym Crow defined an institutional repository as a "digital collection capturing and preserving the intellectual output of a single or multi-university community". Repository servers can help institutions to increase their visibility and, in addition, they are beginning to change the system of scholarly communication.

There are some multi-institutional driven repository servers but most of the repositories are maintained on a single institutional level. Thus the ways and means to present their content to the world naturally vary from simple web sites to database driven systems with OAI interface. The Bielefeld Academic Search Engine (BASE) is a registered OAI service provider which uses the search technology of FAST Search & Transfer and is therefore able to collect and index data from different sources by using the FAST file system import routines, web crawler or specific database connectors. At present, BASE contains principally OAI metadata and in some cases fulltexts from repository servers but it also contains digital text collections, bibliographic data from Springer Publishing and parts of the library catalogue of Bielefeld UL as well as web crawled working papers of the leading German economic research institutes.

This lecture comprehends the creating of the design of BASE, the software, technology and search environment used, the incorporation of resources and the possible fields of application. BASE is a highly flexible search engine system and can be used as an institutional repository search service by creating a special view on accordant collections. This means identifying those resources, harvesting the corresponding metadata by using an open source OAI harvester or crawling them by using the FAST web crawler, preparing these data for the search engine index and displaying them in the BASE user interface.

Because BASE placed emphasis on OAI data, the quality of which differs a lot in practice, we were forced to develop some strategies and technical tools to support the complete data workflow. In addition, we will give an outlook to federated search with BASE and other search engine systems.