References-definitions

STU3 Candidate

This page is part of the FHIR Specification (v1.8.0: STU 3 Draft). The current version which supercedes this version is 5.0.0. For a full list of available versions, see the Directory of published versions . Page versions: R5 R4B R4 R3 R2

FHIR Infrastructure

Work Group

Maturity Level: N/A

Ballot Status: STU 3

Reference
Definition	A reference from one resource to another.
Control	1..1
Summary	true
Comments	References SHALL be a reference to an actual FHIR resource, and SHALL be resolveable (allowing for access control, temporary unavailability, etc). Resolution can be either by retrieval from the URL, or, where applicable by resource type, by treating an absolute reference as a canonical URL and looking it up in a local registry/repository.
Invariants	Defined on this element ref-1: SHALL have a contained resource if a local reference is provided (expression : reference.startsWith('#').not() or (reference.substring(1).trace('url') in %resource.contained.id.trace('ids')), xpath: not(starts-with(f:reference/@value, '#')) or exists(ancestor::[self::f:entry or self::f:parameter]/f:resource/f:/f:contained/f:[f:id/@value=substring-after(current()/f:reference/@value, '#')]\|//f:contained/f:*[f:id/@value=substring-after(current()/f:reference/@value, '#')]))
Reference.reference
Definition	A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.
Control	0..1
Type	string
Summary	true
Comments	Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.
Invariants	Affect this element ref-1: SHALL have a contained resource if a local reference is provided (expression : reference.startsWith('#').not() or (reference.substring(1).trace('url') in %resource.contained.id.trace('ids')), xpath: not(starts-with(f:reference/@value, '#')) or exists(ancestor::[self::f:entry or self::f:parameter]/f:resource/f:/f:contained/f:[f:id/@value=substring-after(current()/f:reference/@value, '#')]\|//f:contained/f:*[f:id/@value=substring-after(current()/f:reference/@value, '#')]))
Reference.identifier
Definition	An identifier for the other resource. This is used when there is no way to reference the other resource directly, either because the entity is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location.
Note	This is a business identifer, not a resource identifier (see discussion)
Control	0..1
Type	Identifier
Summary	true
Comments	When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy. When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.
Reference.display
Definition	Plain text narrative that identifies the resource in addition to the resource reference.
Control	0..1
Type	string
Summary	true
Comments	This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.