Summary
We report on a large-scale knowledge conversion and curation case study. Medical knowledge from a comprehensive, though semantically shallow terminological repository, the UMLS, is transformed into a formally rigorous, expressive description logics format. This way, the broad coverage of the UMLS is combined with inference mechanisms for consistency and cycle checking. They are the key not only to proper cleansing of the knowledge directly imported from the UMLS, but also to subsequent updating and refinement of large amounts of rich and complex terminological knowledge structures. The emerging biomedical ontology currently comprises more than 240,000 conceptual entities and, hence, constitutes one of the largest formal knowledge bases ever built.