---
{
  "title": "FHIR Profiling: Changing Cardinality",
  "description": "One key function of profiles is to modify the cardinality of an element. A profile can restrict an element's cardinality within its base structure.",
  "date": "2025-04-11",
  "author": "Ivan Bagrov",
  "reading-time": "3 min",
  "tags": [
    "FHIR Profiling",
    "FHIR Standard"
  ]
}
---
## FHIR Cardinality in Profiles

One key function of profiles is to modify the cardinality of an element. A profile can restrict an element's cardinality within its base structure.
The foundational FHIR structure defines the following types of cardinality:
- Optional array (0..*)
- Optional scalar (0..1)
- Required array (1..*)
- Required scalar (1..1)

With the following constraints:
- You cannot make a required element that is optional in the base profile. 
- You cannot convert an array element into a scalar if it exists as an array in the base profile. 
- You cannot change a scalar element into an array if it is defined as a scalar in the base profile.

Example of how to create a profile that makes the `Patient.name` field mandatory:


```javascript
resourceType: StructureDefinition
url: http://example.org/fhir/StructureDefinition/patient-with-required-name
name: patient-profile
derivation: constraint
type: Patient
status: active
kind: resource
abstract: false
differential:
  element:
	- id: Patient.name
  	  path: Patient.name
  	  min: 1
  	  max: "*"
```


[Create a profile in your own FHIR server](https://www.health-samurai.io/fhir-server)

See also: [FHIR Profiling](/blog/fhir-profiling) and [How to create a FHIR Implementation Guide](/blog/how-to-create-a-fhir-implementation-guide).