> 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.

# Extensions

This section provides background information about optional tables that can be added to the Output Database that can be used to enhance the queries you can execute. When using the SNOMED CT ontology for data retrieval and analysis, we have found it helpful to leverage concept hierarchies provided by SNOMED. The next section describes how to set up and use the SNOMED CT concept hierarchies in your data queries.

* [Using SNOMED CT Concept Hierarchies](/nlp/database/schema/extensions/snomed-hierarchies)
* [Using SNOMED CT Concept Descriptions](/nlp/database/schema/extensions/snomed-descriptions)