FollowedBy

FHIRConnect follows a top-down approach combined with iterating and accessing paths to execute logic that aligns with child elements. To facilitate this, FollowedBy was introduced. The FollowedBy mechanism allows to attach mappings to each other, ensuring their execution occurs as the next step after the parent mapping method has been executed.

The reason for this is that there are nested paths in FHIR and openEHR. For 0..n root elements, mappings must be executed 0..n times. To execute a mapping for two different child nodes within this path, the with logic is not enough. If we split this into two separate with mappings, they will overwrite each other since both address the same root path.

mappings:
  - name: "period"
    with:
      fhir: "$resource.onset.as(Period)"
      openehr: "$archetype"
      type: "NONE"
    followedBy:
      mappings:
        - name: "start"
          with:
            fhir: "start"
            openehr: "data[at0001]/items[at0077]"

        - name: "lebensphaseCluster"
          with:
            fhir: "$fhirRoot"
            openehr: "data[at0001]/items[openEHR-EHR-CLUSTER.lebensphase.v0]"
          slotArchetype: "CLUSTER.lebensphase.v0"

Here, the onset is accessed if it is a period (FHIRPath helps us here as a shortcut instead of using fhirCondition) and executes a mapping based on the start time of the period. Additionally, we trigger a slot archetype cluster mapping. Slot archetypes are explained in the next chapter.

If it was written as two single with: statements, the cluster mappings would, when converting openEHR to FHIR, overwrite the "start" mapping since it maps the same path.

mappings:
  - name: "start"
    with:
      fhir: "$resource.onset.as(Period).start"
      openehr: "$archetype/data[at0001]items[at0077]"

  - name: "lebensphaseCluster"
    with:
      fhir: "$resource.onset.as(Period)" # same path onset, overwrites start
      openehr: "$archetype/data[at0001]/items[openEHR-EHR-CLUSTER.lebensphase.v0]"
    slotArchetype: "CLUSTER.lebensphase.v0"

More information about recurrence and cardinality see Recurrence

Path construction

All followedBy mappings start with parent’s path. In the example above, resolved path used for actual mapping of - name: "start" would be $resource.onset.as(Period).start. First part being from the parent and the start being from the followedBy mapping. In the same manner, openEHR paths are concatenated.

In case you do not want a followedBy mapping to include another path, you can reference $openehrRoot, $archetype, $fhirRoot or $resource (see: Variables).