Additional Bindings for FHIR Terminology Constraints: Enabling Multiple Definitions on a Single Element

Details

Initially, FHIR operated on a model where every coded element had exactly one binding (ValueSet). While suitable for simple uses, this model hit limits when dealing with international patient data exchange or diverse regulatory requirements. Workarounds like the 'Extensible+Max' pattern and complex slicing were used to address these gaps, but they proved difficult for implementers to understand and verbose to author. This was particularly evident in use cases like the International Patient Summary (IPS), which requires multiple code systems from different jurisdictions. To solve this, Grahame Grieve proposed adding 'additional bindings' to `ElementDefinition.binding`. This allows designers to attach multiple constraints with specific purposes (e.g., required, recommended, UI hint) alongside the main conformance binding. The feature was adopted in R5 as a first-class element. This significantly enhances FHIR's ability to define terminology constraints, allowing developers to express complex and multi-faceted rules using clear semantics.