The Metathesaurus contains over one million concepts. Users create a useful subset, or smaller grouping of concepts, by choosing source vocabularies or applying a filter in MetamorphoSys, the free UMLS installation.
Examples of subsets include:
- Source vocabularies in a language (all Spanish vocabularies)
- All terms that are free for use within the United States
- CPT codes to be used for billing purposes
- Terms with the semantic type 'Clinical Drug'
There are two relational formats for Metathesaurus subsets:
Developers are encouraged to use the RRF which better represents the detailed semantics of each source vocabulary and provides better representations of concept name, source, and hierarchical information.
- Rich Release Format (RRF)
- Original Release Format (ORF)