The UMLS semantic network reduces the complexity of the Metathesaurus by grouping concepts according to the semantic types that have been assigned to them. For certain purposes, however, an even smaller and coarser-grained set of semantic type groupings may be desirable. The following principles were used to design the groupings: semantic validity, parsimony, completeness, exclusivity, naturalness, and utility. The 15 semantic groups provide a partition of the UMLS Metathesaurus for 99.5% of the concepts.
More information about the semantic groups is available in the following papers:
McCray AT, Burgun A, Bodenreider O. Aggregating UMLS semantic types for reducing conceptual complexity. Proceedings of Medinfo 2001;10(Pt 1):216-20. [download PDF].
Bodenreider O, McCray AT Exploring semantic groups through visual approaches. Journal of Biomedical Informatics 2003;36(6):414-432. [download PDF].
The UMLS semantic groups are made available through a file called SemGroups.txt. There is one line in this file for each semantic type. The identifier and the name of the semantic group are repeated for each semantic type included in the group, before the identifier (TUI) and the name (STY) of the semantic type.