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fthe development of numerous shared terminolo-gies in the life sciences are unmatched in most other scientific fields. More than hundred termi-nologies are currently incorporated in the Unified Medical Language System (UMLS)1, while more than fifty terminological resources reside within the Open Biomedical Ontologies (OBO)2 frame-work. In terms of design principles (reflecting different purposes for usage), however, most of the concept systems being developed for medicine and biology differ markedly. While thesauri and classifications in medicine (such as the MeSH3 tages over a purely lexical or thesaurus-like format for terminologies. First, an ontology is an effective means to represent domain knowledge in a coher ent and comprehensive way. Grouping data base entries into explicitly defined classes provides a clean interface between terminological and concep tual knowledge. Second, due to its formal rigor it allows for automated reasoning about the domain classes (e.g., by means of description classifiers) Finally, its clearly defined structure makes it an intuitive means to communicate the information related to the application domain to the users oAn Ontology for Major Histo