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FHIR Profiling

Definition

  • Adapting the FHIR specifications to a particular context of use.
  • Variation in context across the world in the healthcare ecosystem

Profiling Context

Conformance Module

  • Conformance resources represent the adaptations in a computable fashion
  • Implementation Guide (IG) :- describes how FHIR is adapted to support a certain use case.
  • Capability Statement :- Uses Conformance resource to document how a client or server has implemented FHIR

Conformance Resource

  • StructureDefinition Resource :- Defines how resources, extensions and data types are used.
  • MessageDefinition Resource :- Describes messages that can be sent or received
  • OperationDefinition Resource :- Describes addition operations in addition to the base specifications
  • SearchParameter Resource :- Describes additional search capabilities in addition to the base definition
  • CompartmentDefinition Resource :- Describes a logical grouping for resources (used in access control or search)

Conformance Resources Relationship

StructureDefinition Resource

  • This resource is used to define FHIR data structures :-
    • Resource
    • Extension
    • DataTypes
  • Implementors can use this resource to make constraints on the base definition

StructureDefinition Resource Properties

  • url :- Unique identifier for StructureDefinition
  • name :- Name of the StructureDefinition
  • baseDefinition :- base of the current StructureDefinition
  • Snapshot :- This is a fully calculated form of structure
  • Differential :- Only contains constraints made onto the base structure, anything not mentioned in statement is implied to have no changes from the base

$snapshot operation

  • Generates a StructureDefinition instance with a snapshot based on the differential in a specified StructureDefinition.
  • In orde to generate a valid snapshot, baseDefinition of a StrcutureDefinition must have a valid snapshot.
  • Query Structure :-
    • POST :- [base]/StructureDefinition/$snapshot
    • GET, PUT :- [base]/StructureDefinition/[id]/$snapshot

Slicing

  • Slicing is basically restrictions on each element of a resource property with cardinality >= 1.
  • Discriminator :- In order to differentiate between slices, each resource element which is slices will include a property known as the discriminator to tell them apart. The discriminator consists of two mandatory fields :-
    • Type :- Slice Type
    • Path :- FHIRPath expression

Slice Types

Type Use Scenario
value Static comparison Usually used for comparing static codes
exists If the property exists & then another condition Usually used for Backboneelements
pattern Comparing pattern Usually used for CodeSystems like LOINC, SNOMED CT
type value[x]/pattern[x] Usually used for resource properties which support more than one datatype or primitive types
profile Validate data type against profile Used for validating datatype with a custom profile

Slicing Rules

When an element of a fixed cardinality m..n is sliced, the following rules apply: -

  • Each slice cannot have a greater cardinality than the maximum number of slices allowed.
  • The sum of the maximum cardinalities can be larger than n.
  • The sum of the minimum cardinalities must be less or equal to n.
  • Each individual slice can have a minimum cardinality of 0 (less than m - the only situation where this is allowed), but the total number of elements in the instance must still be greater or equal to m.

$validate Operation

  • The validate operation checks whether the attached content would be acceptable while performing CRUD operations.
  • Query structure :-
    • POST :- [base]/Resource/$validate
    • GET, PUT, DELETE :- [base]/Resource/[id]/$validate

Extensions

  • Creating extensions inside a profile by using a StructureDefinition resource
  • Define context i.e. where can it be used, target structure: resource, datatype, extension
  • Example :- US Core Patient Profile