FHIR Reference Explained: Relative, Absolute, Contained, and Bundle Links

Details

In FHIR, when one resource (like Observation) needs to reference another (like Patient), it uses a 'Reference' mechanism rather than embedding the full resource. The Reference data type in FHIR R4 consists of elements such as `reference` (relative/absolute URL), `identifier` (business ID), `type` (expected resource type), and `display` (human-readable description). A key focus is on how different link formats behave. Examples include Relative references (based on the service base), Absolute references (matching a full URL), Contained references (pointing to resources within the current container), and Version-specific references (targeting specific versions). The text also details reference resolution within a Bundle. Each entry in a Bundle requires a `fullUrl`. For relative references, the processor combines this `fullUrl` with the service root to determine the target URL, illustrating that simple ID comparison is insufficient for accurate bundle resolution. This highlights the complexity of connecting separate pieces of information using standardized links.