# Related Persons
This page discusses the manner in which FHIR RelatedPerson resources are handled and the various caveats of how those relate to the iCDR relationships.
## CDR Relationships
The CDR storage model support robust linkages between patients and persons. Some SanteDB services such as the Immunization Management Service (IMS) represent relationships between non-patient persons as a direct relationship between an instance of a Patient entity and a Person entity with a relationship type.
This example illustrates a simple non-patient entity (Sarah Smith) is the mother of a Patient (Baby Joe Smith).
Additionally, the CDR also supports the direct linking of patient entities to other patient entities in relationships. The illustration below illustrates a patient entity (Sarah Smith) is the mother of Patient (Baby Joe Smith).
This relationship works because in SanteDB a Patient **is a** Person.
## FHIR Relationships
In FHIR, the `RelatedPerson` resource is used to represent a related person. Unlike SanteDB's RIM model, FHIR's `RelatedPerson` maps to one of the following internal concepts in SanteDB:
* A combination of `Person` and `EntityRelationship` where the `Person` may only contain one relationship to one `Patient`, or
* An `EntityRelationship` only, where only the relationship type is expressed.
A `RelatedPerson` represents a combination of `Person`and `EntityRelationship` when it is expressed as:
```javascript
{
"resourceType": "RelatedPerson",
"id": "123",
"patient": {
"reference": "Patient/321"
},
"relationship": [
{
"coding": [
{
"system": "http://terminology.hl7.org/CodeSystem/v3-RoleCode",
"code": "MTH"
}
]
}
],
"name": [
{
"use": "usual",
"given": [
"SU MYAT LWIN"
]
}
],
"gender": "female"
}
```
This condition is described in the section Simple Relationships on this page. However, a `RelatedPerson` is only an `EntityRelationship` when it is represented as:
```javascript
"entry": [
...
{
"fullUrl": "RelatedPerson/123",
"resource": {
"resourceType": "RelatedPerson",
"id": "123",
"patient": {
"reference": "Patient/ohie-cr-05-20-fhir-baby"
},
"relationship": [
{
"coding": [
{
"system": "http://terminology.hl7.org/CodeSystem/v3-RoleCode",
"code": "MTH"
}
]
}
]
}
},
{
"fullUrl": "Patient/123",
"resource": {
"resourceType": "Patient",
"id": "123",
"name": [
{
"use": "maiden",
"given": [
"SU MYAT LWIN"
]
}
],
"gender": "female",
"birthDate": "1984-05-25",
"link": [
{
"other": {
"reference":"RelatedPerson/123"
},
"type": "seealso"
}
]
}
}
]
```
The behavior of the iCDR is described in Complex Relationships in this page.
### Simple Relationships
The manner in which HL7 FHIR views patient relationships is reversed from the CDR's view of relationships. Primarily, HL7 FHIR would represent a non-patient person relationship to a patient as.
In effect, the FHIR resource `RelatedPerson` is a mashup of a `Person` and an `EntityRelationship`, as the `RelatedPerson` contains elements of both objects.
The CDR handles these relationship types automatically. When querying from FHIR with `_revInclude=RelatedPerson:patient` , the CDR will interpret either of these relationships and will construct the appropriate response messages for broadcasts and searches.
The CDR will treat the target of the personal relationship as a Person. Since the CDR support hierarchy and Patient is a Patient, this translation is transparent to the FHIR interface. The CDR treats the instance of `RelatedPerson` as the `EntityRelationship` instance between the two entities. The CDR's FHIR plugin will reverse the relationship to ensure that the FHIR `RelatedPerson` references is correctly associated.
{% hint style="info" %}
The reason the RelatedPerson is linked to the EntityRelationship is a single Person may have multiple relationships (for example, a mother of two children). However, in FHIR a RelatedPerson may only have a single relationship between a Person and a Patient.
{% endhint %}
This behaviour matches the HL7 processor when an NK1 segment is present. For example, this HL7 message
```
MSH|^~\&|TEST|TEST|CR1|MOH_CAAT|20211104174451|DEVICESECRET|ADT^A01^ADT_A01||P|2.3.1
EVN||20211020
PID|||HL7-3^^^TEST||SMITH^BABY JOE^^^^^L|SMITH^SARAH^^^^^|20210123|M|||||||||||
NK1||SMITH^SARAH|MTH||||E|||||||||19840503|||US|EN||||||||||||234^^^TEST
```
And this FHIR message
```javascript
{
"resourceType": "Bundle",
"type": "transaction",
"entry": [
{
"fullUrl": "Patient/1",
"resource": {
"resourceType": "Patient",
"id": "1",
"active": true,
"identifier": [
{
"use": "official",
"system": "http://santedb.org/fhir/test",
"value": "HL7-3"
}
],
"name": [
{
"use": "usual",
"family": "SMITH",
"given": [
"BABY", "JOE"
]
}
],
"gender": "male",
"birthDate": "2021-01-23"
},
"request": {
"method": "POST",
"url": "Patient/1"
}
},
{
"fullUrl": "RelatedPerson/1",
"resource": {
"resourceType": "RelatedPerson",
"id": "1",
"patient": {
"reference": "Patient/1"
},
"relationship": [
{
"coding": [
{
"system": "http://terminology.hl7.org/CodeSystem/v3-RoleCode",
"code": "MTH"
}
]
}
],
"name": [
{
"use": "usual",
"family": "SMITH",
"given": [
"SARAH"
]
}
],
"gender": "female"
},
"request": {
"method": "POST",
"url": "RelatedPerson/1"
}
}
]
}
```
Will both result in this structure in the database.
### Complex Relationships
Relationships between Patients in FHIR are slightly more complex, take for example, a scenario where a Sarah Smith is a patient and is related to Baby Joe Smith. In FHIR the structure of this message would be as follows.
The HL7 FHIR processor on a read will not reproduce this when a patient is read from the database and is directly related to another patient. Instead the simple case of representation is performed on a query.
When creating or updating a related person in this manner the following structure is created in the RIM structure.
This structure is also created from the HL7v2 process when an NK1 segment points at a previously registered PID segment. For example, the following HL7v2 structure also creates a similar structure as the FHIR interface.
```
MSH|^~\&|TEST|TEST|CR1|MOH_CAAT|20211104174451|DEVICESECRET|ADT^A01^ADT_A01||P|2.3.1
EVN||20211020
PID|||234^^^TEST||SMITH^SARAH|19840503|M
MSH|^~\&|TEST|TEST|CR1|MOH_CAAT|20211104174451|DEVICESECRET|ADT^A01^ADT_A01||P|2.3.1
EVN||20211020
PID|||HL7-3^^^TEST||SMITH^BABY JOE^^^^^L|SMITH^SARAH^^^^^|20210123|M|||||||||||
NK1||SMITH^SARAH|MTH||||E|||||||||19840503|||US|EN||||||||||||234^^^TEST
```
This structure will indicate that a patient is admitted to hospital (Sarah Smith) and then is linked to Baby Joe Smith as a next of kin. In FHIR this structure is represented as.
```javascript
{
"resourceType": "Bundle",
"type": "transaction",
"entry": [
{
"fullUrl": "Patient/1",
"resource": {
"resourceType": "Patient",
"id": "1",
"active": true,
"identifier": [
{
"use": "official",
"system": "http://santedb.org/fhir/test",
"value": "HL7-3"
}
],
"name": [
{
"use": "usual",
"family": "SMITH",
"given": [
"BABY", "JOE"
]
}
],
"gender": "male",
"birthDate": "2021-01-23"
},
"request": {
"method": "POST",
"url": "Patient/1"
}
},
{
"fullUrl": "RelatedPerson/1",
"resource": {
"resourceType": "RelatedPerson",
"id": "1",
"patient": {
"reference": "Patient/1"
},
"relationship": [
{
"coding": [
{
"system": "http://terminology.hl7.org/CodeSystem/v3-RoleCode",
"code": "MTH"
}
]
}
]
},
"request": {
"method": "POST",
"url": "RelatedPerson/1"
}
},
{
"fullUrl": "Patient/2",
"resource": {
"resourceType": "Patient",
"id": "2",
"active": true,
"identifier": [
{
"use": "official",
"system": "http://santedb.org/fhir/test",
"value": "0234"
}
],
"name": [
{
"use": "usual",
"family": "SMITH",
"given": [
"SARAH"
]
}
],
"gender": "male",
"birthDate": "1984-05-03",
"link": {
"type" : "seealso",
"other" : {
"reference": "RelatedPerson/1"
}
},
"request": {
"method": "POST",
"url": "Patient/1"
}
}
]
}
```
## Special Implementation Notes for Related Person
* When querying a patient which has a relationship with another patient (for example, querying for `?identifier=HL7-3` ) you can use `_revInclude=RelatedPerson:patient` to join a RelatedPerson instance, however the included `RelatedPerson` instance will be represented as a simple relationship rather than a complex relationship.
* It is not possible to perform a `_revInclude=Patient:link` on order to retrieve patient information about the `RelatedPerson` , this is because there is no relationship or link per-se between the `Person` and `Patient`, in SanteDB **they are the same resource**
* The `id` and `fullUrl` of the `RelatedPerson` is the `id` property of the `EntityRelationship` rather than the `Person`. This is because in FHIR a `RelatedPerson` can have **exactly one** relationship to **exactly one** `Patient`, however in SanteDB RIM a `Person` can have **infinite** relationships to **infinite** `Patient` resources.
* When querying directly for a `Patient` instance on the FHIR interface, you may see one or more `link` properties such as listed below, this link information is provided to indicate there exists a relationship where the patient is a target of a relationship.
```markup
```
{% hint style="info" %}
When MDM is enabled, the **Master/Golden** record is returned on queries, since no relationships can exists between a local to a master the master results will not return seealso links to RelatedPerson instances (since they are not pointed at data).
{% endhint %}
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