Several information models have been developed for the Unified Medical Language System (UMLS). While some models are term-oriented, a knowledge-oriented model is needed for representing semantic locality, i.e. the various semantic links among concepts. We propose an objectoriented model in which the semantic features of the UMLS are made available through four major classes for representing Metathesaurus concepts, semantic types, interconcept relationships and Semantic Network relationships. Additional semantic methods for reducing the complexity of the hierarchical relationships represented in the UMLS are proposed. Implementation details are presented, as well as examples of use. The interest of this approach is discussed.