The search engine BASE (Bielefeld Academic Search Engine) which is a tool for searching Open Access contents and automatic classification is active since 2004 and includes 37,4 million documents from 2900 mostly academic repositories. Special features are a truncation function, a search history, sorting, a drilldown function and the cooperation of linguistic tools. Interoperability is guaranteed through the possibility to bind BASE to different interfaces.

Harvesting OAI-PMH interfaces, BASE is challenged by the integration of the search results like i.e. by the combination of links, corresponding metadata and the full text access of one source. The BASE initiative furthermore tries to normalize and enhance the metadata quality of difference source values like i.e. language values or the type of publication as the descriptions vary from each other in order to better aggregate similar contents.

BASE uses the information about subject repositories from registries like OpenDOAR and Disciplinary repositories. Still the objective of BASE is automatic classification by the automatic analysis of content information and the building of a knowledge database to provide an additional subject-based browsing.