Concepts and Synonymy in the UMLS Metathesaurus

This paper advances a detailed exploration of the complex relationships among terms, concepts, and synonymy in the UMLS (Unified Medical Language System) Metathesaurus, and proposes the study and understanding of the Metathesaurus from a model-theoretic perspective. Initial sections provide the background and motivation for such an approach, and a careful informal treatment of these notions is offered as a context and basis for the formal analysis. What emerges from this is a set of puzzles and confusions in the Metathesaurus and its literature pertaining to synonymy and its relation to terms and concepts. A model theory for a segment of the Metathesaurus is then constructed, and its adequacy relative to the informal treatment is demonstrated. Finally, it is shown how this approach clarifies and addresses the puzzles educed from the informal discussion, and how the model-theoretic perspective may be employed to evaluate some fundamental criticisms of the Metathesaurus. For users of the UMLS, two significant results of this analysis are a rigorous clarification of the different senses of synonymy that appear in treatments of the Metathesaurus and an illustration of the dangers in computing inferences involving ambiguous terms.