> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.emtelligent.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.emtelligent.com/_mcp/server.

# Concept Hierarchy Queries

> **Warning**
>
> The SQL queries in this section require that you extend the Output Database by adding the Snomed relationship definitions table. You can download the SQL file containing these definitions and install them following these [instructions](/nlp/database/schema/extensions/snomed-hierarchies#adding-snomed-relationships-to-output-database).

Concept hierarchies allow you to conveniently find a large set of related terms specifying only a single concept. It is a powerful query pattern, and makes the initial setup well worth the effort. An explanation of the SNOMED ontology, and how it encodes relationships between concepts, is found [here](/nlp/database/schema/extensions/snomed-hierarchies).