Fast Healthcare Interoperability Resources (FHIR) specifies resources, operations, coded data types and terminologies that are used for representing and communicating coded, structured data in the FHIR core specification within its Terminology Module.
Snow Owl's pluggable and extensible architecture allows modular development of the FHIR API both in terms of the supported functionality as well as the exposed terminologies. Additionally, Snow Owl's revision-based model allows the concurrent management of multiple versions.
The Snow Owl terminology server's FHIR API release includes support for the following resources:
Snow Owl's repository is a fully-fledged revision control system with branches, versions and revisions. Snow Owl's terminology artefact versions are exposed as FHIR versions for every supported code system with the exception of SNOMED CT where the standard SNOMED CT URI specification governs the format (short date) of the version. If there is no version specified in a request, the last version is assumed. If there is no version in the system, the last state (head of MAIN) is considered.
The supported search result filters:
_summary
_elements
The supported search parameters:
_id
Sorting and paging are not yet supported.
Globally unique logical URIs that represent a terminology resource. For code systems these are:
For SNOMED CT, Snow Owl's FHIR implementation follows the SNOMED CT URI Standard.
For ICD-10, Snow Owl's FHIR implementation follows the HL7 FHIR Specification.
Snow Owl's Local Code Systems (LCS) identified by the URI that is based on the Organization Link property stored within Snow Owl's Terminology Registry and the Short Name of the LCS e.g.: https://b2i.sg/MyLocalCodeSystem.
The id field of each terminology resource is assigned by our terminology server and is unique within Snow Owl. Once is has been assigned, the id never changes. For this logical identifier, Snow Owl follows the pattern:
For example to identify a particular LOINC code system with the version tag 20180131:
For example to address a particular SNOMED CT concept (Blood bank procedure):
where
59524001 represents the concept id
20140203 represents the extension version
DK represents the extension branch
20110131 represents the version of the International Edition the DK extension is based on
Our logical id has been extended to cover individual Reference Set members as well:
where
98403008 is the Reference Set ID
98484f56f72-9f8b-423d-98b8-25961811393c03008 is the reference set member
Snow Owl exposes a comprehensive REST API to support areas such as:
Syndication - content provisioning between servers or between the Snow Owl Authoring platform and servers
Administration (repository and revision control management)
Auditing
SNOMED CT specific browsing and authoring API
Currently only JSON format is supported with UTF-8 encoding and content type of Content-Type = application/fhir+json;charset=utf-8. In case of any errors during the processing the API responds with an OperationOutCome within the response body using one of the HTTP status codes:
Code system
URI
ATC
SNOMED CT
ICD-10
LOINC
FHIR
Prefixed with http://hl7.org/fhir
LCS
Prefixed with the organization link
Value Set
Prefixed with the source URI
Mapping Set
Prefixed with the source URI
HTTP Status
Reason
200
OK
400
Bad Request
401
Unauthorized
403
Forbidden
404
Not Found
500
Internal Error
Code systems maintained within Snow Owl are exposed (read-only) via the endpoints /CodeSystem and /CodeSystem/{codeSystemId}. Supported concept properties are handled and returned if requested. The currently exposed code systems are:
Snow Owl OSS:
SNOMED CT
Internal (FHIR) Code Systems (terminology subset)
Snow Owl Pro:
ATC
ICD-10
LOINC
OPCS
All standard and default SNOMED CT properties are supported, including the relationship type properties. In addition to the FHIR SNOMED CT properties, Snow Owl can return the effective time property, with the URI http://snomed.info/field/Concept.effectiveTime.
Both GET as well as POST HTTP methods are supported. Concepts are queried based on code, version, system or Coding. Designations are included as part of the response as well as supported concept properties when requested. No date parameter is supported.
For SNOMED CT, all common and SNOMED CT properties are supported, including all active relationship types.
Both GET as well as POST HTTP methods are supported. Subsumption testing is supported for ICD-10 and SNOMED CT terminologies.
The endpoints /ConceptMap and /ConceptMap/{conceptMapId} and corresponding operations expose the following types of terminology resources:
SNOMED CT Simple Map Reference Sets with Concepts as referenced components
SNOMED CT Complex Map Reference Sets
SNOMED CT Extended Map Reference Sets
Snow Owl's generic Mapping Sets
All concept map accessible via the /ConceptMap endpoints are considered when retrieving mappings (translations). The translate request's source that designates the source value set cannot be interpreted hence not used. With the exception of SNOMED CT where the standard URI is expected, our proprietary short name or component ids are used to designate the source/target code system.
SNOMED CT:
Simple Map Type Reference Set mappings are considered equivalent in terms of their correlation
The availability and format of target code systems are not guaranteed, there is an ongoing conversation at SNOMED CT International to rectify this.
The endpoints /ValueSet and /ValueSet/{valueSetId} and corresponding operations expose the following types of terminology resources:
SNOMED CT Simple Type Reference Sets with Concepts as referenced components.
SNOMED CT Query Type Reference Sets with ECL expressions (each member is a Value Set)
Snow Owl's generic Value Sets
Delete and create operations are not implemented.
All value sets accessible via the /ValueSet endpoints can be expanded.
For SNOMED CT URIs, implicit value sets are supported:
?fhir_vs - all Concept IDs in the edition/version. If the base URI is , this means all possible SNOMED CT concepts
?fhir_vs=isa/[sctid] - all concept IDs that are subsumed by the specified Concept.
?fhir_vs=refset - all concept ids that correspond to real references sets defined in the specified SNOMED CT edition
?fhir_vs=refset/[sctid] - all concept IDs in the specified reference set
The in-parameters are not yet supported.
Codes can be validated against a given Value Set specified by the value set's logical id or canonical URL. In terms of Snow Owl terminology components, codes are validated against:
SNOMED CT Simple Type Reference Sets with Concepts as referenced components.
SNOMED CT Query Type Reference Sets with ECL expressions (each member is a Value Set)
Snow Owl's generic Value Sets
Validation performs the following checks:
The existence of the given Value Set (error if not found)
The existence of the reference in the existing Value Set to the given code (error if not found)
The existence of the given code in the system (error if not found)
Potential version mismatch (_error if the reference points to a version that is different to the code's version)
The status of the given code and reference (warning if code is inactive while reference is active)
For SNOMED CT URIs, implicit value sets are supported:
?fhir_vs=isa/[sctid] - all concept IDs that are subsumed by the specified Concept.
?fhir_vs=refset - all concept ids that correspond to real references sets defined in the specified SNOMED CT edition
?fhir_vs=refset/[sctid] - all concept IDs in the specified reference set
?fhir_vs - all Concept IDs in the edition/version. If the base URI is , this means all possible SNOMED CT concepts