Can a

ValueSet

URL be used in place of a

CodeSystem

? For instance, I'd like to use http://hl7.org/fhir/ValueSet/relatedperson-relationshiptype for a

RelatedPerson

relationship but the

system

coming back from the

CodeInput

results are on of the composed `CodeSystem`'s and as such, I'd need some client logic to check and find the relationship by understanding `relatedperson-relationshiptype`'s composition. Alternatively, I could just hardcode the relationship->coding->system to http://hl7.org/fhir/ValueSet/relatedperson-relationshiptype but I'm not sure if this is a valid use of the

system

field for a

Coding

value.

In general, it's considered a bit of an anti-pattern to use the ValueSet URL as the system string. The

system

is very much meant to identify the standardized coding system from which the value was taken. There is a many to many relationship between

ValueSets

and

CodeSystems

- a

ValueSet

can include values from multiple

CodeSystems

, and the

CodeSystem

share values with multiple

ValueSets

Some more info on system strings here: https://www.medplum.com/blog/demystifying-fhir-systems

Ya so in order for my client application to extract the

relatedperson-relationshiptype

value for a

RelatedPerson

, the client needs to encode the http://hl7.org/fhir/ValueSet/relatedperson-relationshiptype composition:

System http://terminology.hl7.org/CodeSystem/v2-0131
System http://terminology.hl7.org/CodeSystem/v3-RoleCode
  Filter
    Property concept
    Op is-a
    Value _PersonalRelationshipRoleType

So I would have to search through

RelatedPerson.relationship.coding

and check for system

http://terminology.hl7.org/CodeSystem/v2-0131

or

http://terminology.hl7.org/CodeSystem/v3-RoleCode

where the filter matches To simplify the client lookup, I just hardcode the system to http://hl7.org/fhir/ValueSet/relatedperson-relationshiptype which felt wrong from a FHIR standpoint (because this is not a standard CodeSystem) but also makes the clients job much easier as it just needs to search

relationship.coding

for the system

http://hl7.org/fhir/ValueSet/relatedperson-relationshiptype

.

HI @node , I understand the problem here and understand the challenge. I've been looking for an elegant solution for you. I do have some thoughts here, but nothing that is the most elegant. Given that, I'll concede that using the ValueSet URL might be the way to go. 1. The right way to do this would be to use the

:in

search parameter - you can query if a certain code is in a valuset. However, you would have to mak an API call for each check, which is much more inefficient 2. You could also use the

CodeSystem/$lookup

operation on any codes from http://terminology.hl7.org/CodeSystem/v3-RoleCode/ . This operation returns all properties of a given code, including whether or not the code

isa _PersonalRelationshipRoleType

. Again, however, this requires an API lookup https://build.fhir.org/terminology-service.html#lookup