The paper presents a review of the ONIONS project. ONIONS is committed to developing a large­scale ontology library for medical terminology. The developed methodology exploits a description logic­based design for the modules in the library and makes extended use of generic theories, thus creating a stratification of the modules. Terminological knowledge is acquired by conceptual analysis and ontology integration over a set of authoritative sources. After addressing general issues about conceptual analysis and integration, the methodology is briefly described. The central part of the article presents the investigation we have made on the 476,000 medical concepts singled out by the National Library of Medicine as the Metathesaurus^TM in the UMLS project. This is followed by several case studies concerning lexical polysemy, the interface between ontologies and lexicon, and other special problems encountered in the specification of the ontologies. A section describing the current structure of the library and the generic theories reused is provided. Current results of our research include the integration of some top­level ontologies in the ON9.2 ontology library, and the formalization of the terminological knowledge in the UMLS Metathesaurus.

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We describe ONIONS, a methodology for integrating ontologically-heterogeneous taxonomic knowledge and its current application to medical domain. Some clarification is given of our intended meaning of ontology and related notions, then main problems of ontology design are addressed, with a short comparison with alternative approaches. The methodology is described as a sequence of phases. The top-level of the current integrated ontology of heterogeneous medical taxonomies is presented in an order-sorted logic. ONIONS includes no claim of global objectivity (it performs an integration of explicit ---or explicited--- ontologies of given taxonomic sources), but provides a feasible solution to the problems of modelling stopover and cognitive basicality. ONIONS has been defined in order to be applied to sources within the same domain, nevertheless it has been applied to a very wide and inherently heterogeneous domain like medicine, so complex that it can be considered in itself an integration of subdomains. 1.