Unified Medical Language System® (UMLS®) Basics

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.

The graphic above illustrates two semantic relationships:  

Current semantic types and semantic relationships are listed online.