Implementing Terminology Services with SNOMED CT

A number of FHIR Terminology Service Operations have unique considerations when working with SNOMED CT

Operation Name	Resource	Considerations	Priority for implementation

Operation Name	Resource	Considerations	Priority for implementation
$validate-code	ValueSet	Further discussion by the SNOMED on FHIR working group can be read here: Implementing Terminology Services with SNOMED CT	2b
$validate-code	CodeSystem		2b
$expand	ValueSet	Implicit valuesets (Valuesets defined using ECL), filters, POST (upload) valuesets	1
$lookup	CodeSystem		2
$translate	ConceptMap		5
$subsumes	CodeSystem		3
$closure	ConceptMap		4
$find-matches	CodeSystem	See Find Matches, however using the $expand operation with ECL will allow for more expressive querying.	6

Best Practice Discussions

Paging - note that the $expand operation defines its own offset and count (count be 0 if you're interested in the total number of matches)

Limits on value set sizes - 1M configurable limit, default page size of 1K

Default language considerations - http headers, server settings (Link to Reuben's work and discussion of X-headers for LangRefsets)

Algorithms for text searching (reference implementation course eg "PNE PNE" finding Pneumococcal pneumonia)