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Unified Medical Language System® (UMLS®)

The Semantic Network

The Semantic Network consists of:

  • Semantic types (high level categories)
  • Semantic relationships (relationships between semantic types)

The Semantic Network can be used to categorize any medical vocabulary.

There are 133 semantic types in the Semantic Network. Every Metathesaurus concept is assigned at least one semantic type; very few terms are assigned as many as five semantic types. Semantic types are listed in the Metathesaurus file MRSTY.RRF.

Semantic types and semantic relationships create a network that represents the biomedical domain.

Semantic types and relationships help with interpreting the meaning that has been assigned to the Metathesaurus concept.

a pair of semantic relations
The graphic above illustrates two semantic relationships:

Semantic Type 1 Semantic Relationship Semantic Type 2
Injury or Poisoning disrupts Fully Formed Anatomical Structure
Injury or Poisoning disrupts Physiologic Function


Current semantic types and semantic relationships are listed online.

Last Reviewed: July 29, 2016