Proposal for ConceptReference

This page documents rationale for a proposed enhancement for FHIR, the creation of a new datatype called ConceptReference

Rationale

As of R4, it's pretty common to see this pattern in FHIR:

   MedicationRequest
   - reasonCode : CodeableConcept [0..*] //  Reason or indication for ordering or not ordering the medication
   - reasonReference : Reference(Condition | Observation) [0..*] // Condition or observation that supports why the prescription is being written
   

Or, a variant:

   MedicationRequest
   - medication[x] : CodeableConcept | Reference(Medication) [1..1] // Medication to be taken

These differ because of cardinality of the element, and a methodology limitation from the way we use JSON - choice elements can't repeat.

This pattern - in either form - is pretty clunky; no one likes it. But the idea of en element that provides information about what or why is happening, and that does so by referencing either a very specific piece of information, or just a general conceptual description of it by reference to some concept in a code system or ontology is a pretty common pattern in FHIR.

Common enough to want a better way to do the two examples above, that's for sure.

Proposal

Definition

The proposal is define a new type, ConceptReference.

   ConceptReference  : Reference {
     concept : CodeableConcept [0..1] // a reference to a code system or ontology that describes the essential properties of what is/might be referenced
   }

This type is a specialization of Reference, so shares the same properties. Note, for clarity, that this doesn't mean it can be substituted for any Reference - all FHIR data type bindings are ```final``` (in the OO sense), so this type could only be used where it is explicitly defined as the type for the element.

The ConceptReference type can have a binding to a value set, which just automatically applies to the concept element (pass through)

btw, Alternative possible names: ReferenceOrConcept, CodeableReference

Use =

Using this would be simple

   MedicationRequest
   - medication : ConceptReference(Medication) [1..1] // Medication (code or details) to be taken
   - reason : ConceptReference(Condition | Observation) [0..*] //  Condition or observation (instance or concept) for ordering or not ordering the medication

The actual instance doesn't change all that much (in JSON):

     "medicationReference": {
       "reference": "Medication/X"
     },
     "reasonCode": [
       {
         "coding": [
           {
             "system": "http://snomed.info/sct",
             "code": "11840006",
             "display": "Traveller's Diarrhea (disorder)"
           }
         ]
       }
     ]

changes to

     "medication": {
       "reference": "Medication/X"
     },
     "reason": [
       {
         "concept" : {
           "coding": [
             {
               "system": "http://snomed.info/sct",
               "code": "11840006",
               "display": "Traveller's Diarrhea (disorder)"
              }
           ]
         }
       } 
     ]

and this

   {
     "medicationCodeableConcept": {
       "coding": [
         {
           "system": "http://snomed.info/sct",
           "code": "317935006",
           "display": "Chlorthalidone 50mg tablet (product)"
         }
       ]
     },
     "reasonReference": [
       {
         "reference": "Condition/f201",
         "display": "condition for prescribing this medication"
       }
     ]
   }

changes to

   {
     "medication": {
       "concept" : {
         "coding": [
           {
             "system": "http://snomed.info/sct",
             "code": "317935006",
             "display": "Chlorthalidone 50mg tablet (product)"
           }
         ]
       }
     },
     "reason": [
       {
         "reference": "Condition/f201",
         "display": "condition for prescribing this medication"
       }
     ]
   }