Updating the UMLS Metathesaurus: A Model

The Unifled Medical Language System (UMLS) is intended to support uniform access of machine-readable biomedical information resources. The foundation of the UMLS is a Metathesaurus, which will link terms in different biomedical nomenclatures. Because the resources and nomenclatures continue to evolve, the Metathesaurus must evolve with them. Thus, an important criterion for the design of the Metathesaurus is the graceful accommodation of change. A model of such accommodation is presented. A key design decision was the representation of the Metathesaurus, and prospective updates, as a database of "facts." Particular emphasis is placed on database operations that use the results of inter-nomenclature lexical matching to collapse entries from different nomenclatures into Metathesaurus entries. The implementation of this model for a simplified version of the Metathesaurus is described. 1. THE METATHESAURUS UPDATE PROBLEM Databases and user interfaces to them are important in both computer science and medical informatics. Relational database management systems, distributed databases on heterogeneous computing platforms, and bit-mapped graphic interfaces to databases are active research areas in computer sciencel. These topics are relevant to medical infonnatics in general and to the Unified Medical Language System (UMLS) in particular. The objectives, development strategies, and underlying assumptions of the UMLS have been described by Lindberg and Humphreys.2' The UMLS Metathesaurus, which will be described below, will provide a means of relating the contents of disparate biomedical information sources that are available in electronic form. Because of the volume of information in these sources and the rate at which it changes, updating the UMLS Metathesaurus is a significant problem. This paper begins to address this problem by presenting a model for updating a simplified version of the Metathesaurus. 1.1. THE UWAU AND THE AETATHESAURUS Like the familiar Roget's Thesaurus4, the Metathesaurus will represent altemative ways of saying the same thing and alternative ways of saying related things. It is a Metathesaurus in the sense that it "transcends" a thesaurus by containing information about how biomedical concepts are represented in many different thesauri and controlled vocabularies. The first official version of the UMLS Metathesaurus will include terms from MeSH (Medical Subject Headings), SNOMED (Systematized Nomenclature of Medicine), ICD (Intemational Classification of Diseases), and CPT (Current Procedural Tenminology). The Metathesauns TemlIate How should meaning be represented within the Metathesaurus? This task has been approached by means of a template, which contains slots that will be occupied by text objects. The relationships among these various objects will be defined by the slots into which they are placed The Mark S. Tuttle Lexical Technology, Inc. 1000 Atlantic Avenue, Suite 106