SQL on FHIR (PSS-2716)

SQL on FHIR provides a standard, implementation-agnostic method for defining views that produce tabular data from FHIR resources. The specification uses FHIRPath expressions to describe how to transform FHIR's nested JSON or XML structures into simple tables compatible with SQL databases, data science tools, spreadsheets, and business intelligence platforms. View definitions are declarative specifications that can be written once and executed across diverse technology platforms.

The specification was developed over 18 months by an international working group through an open, collaborative process including weekly public meetings, presentation at HL7 FHIR Connectathon events, and validation through multiple independent implementations. The work has been peer-reviewed and published in npj Digital Medicine (Nature), demonstrating feasibility by replicating a clinical research study across multiple implementations. Eight independent implementations currently exist across platforms including Apache Spark, PostgreSQL, DuckDB, and others. The specification has also been integrated into the HL7 Implementation Guide Publisher.

The specification deliberately constrains its scope to FHIR-to-tabular transformation only, allowing integration with existing SQL and analytics tools rather than attempting to replace them. View definitions handle nested and repeating FHIR data structures, provide abstractions for joining data across related resources, and include a profile architecture (base, shareable, tabular) that supports both ad-hoc use and standardised distribution. The ViewDefinition resource is a FHIR conformance resource that follows the same patterns as other infrastructure resources like StructureDefinition and CapabilityStatement.

This project aims to bring the existing SQL on FHIR specification, with its current feature set, into the HL7 ballot process under FHIR Infrastructure Work Group sponsorship. The specification aligns with FHIR-I's charter for developing core capabilities, conformance resources, and publication tooling. The FHIR Implementation Guide will include the ViewDefinition resource specification, profile architecture (base, shareable, tabular), FHIRPath subset specification, examples, and implementation guidance. The intention is to first ballot the existing specification; new features are planned for subsequent work.