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Identifies two or more records (resource instances) that refer to the same real-world "occurrence".

### Schema

### Elements

| Name             | Required | Type                                                                                          | Description                                                                                                                                                                                                                                                                                                                  |
|------------------|----------|-----------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| active           |          | boolean                                                                                       | Whether this linkage assertion is active or not<br>Details<br>Indicates whether the asserted set of linkages are considered to be "in effect". If false, any asserted linkages should not be considered current/relevant/applicable.                                                                                     |
| author           |          | Reference< [Practitioner](/content/docs/api/fhir/resources/practitioner/index.html)<br> \\| [PractitionerRole](/content/docs/api/fhir/resources/practitionerrole/index.html)<br> \\| [Organization](/content/docs/api/fhir/resources/organization/index.html) > | Who is responsible for linkages<br>Details<br>Identifies the user or organization responsible for asserting the linkages as well as the user or organization who establishes the context in which the nature of each linkage is evaluated.                                                                                   |
| item             | ✓        | LinkageItem\[\]                                                                             | Item to be linked<br>Details<br>Identifies which record considered as the reference to the same real-world occurrence as well as how the items should be evaluated within the collection of linked items.                                                                                                                |
| id               |          | string                                                                                        | Unique id for inter-element referencing<br>Details<br>Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.                                                                                                                                    |
| extension        |          | [Extension](/content/docs/api/fhir/datatypes/extension/index.html)\[\]                  | Additional content defined by implementations<br>Details<br>May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions.                        |
| modifierExtension|          | [Extension](/content/docs/api/fhir/datatypes/extension/index.html)\[\]                  | Extensions that cannot be ignored even if unrecognized<br>Details<br>May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants.                                 |
| type             | ✓        | code                                                                                          | source \| alternate \| historical<br>Details<br>Distinguishes which item is "source of truth" (if any) and which items are no longer considered to be current representations.                                                                                                                                           |
| resource         | ✓        | Reference<Resource>                                                                           | Resource being linked<br>Details<br>The resource instance being linked as part of the group.

### Search Parameters

| Name   | Type     | Description                                               | Expression                           |
|--------|----------|-----------------------------------------------------------|--------------------------------------|
| author | reference| Author of the Linkage                                    | Linkage.author                      |
| item   | reference| Matches on any item in the Linkage                      | Linkage.item.resource               |
| source | reference| Matches on any item in the Linkage with a type of 'source' | Linkage.item.resource               |

### Inherited Elements

| Name             | Required | Type                                                                                          | Description                                                                                                                                                                                                                                                                                                                  |
|------------------|----------|-----------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| id               |          | string                                                                                        | Logical id of this artifact<br>Details<br>The logical id of the resource, as used in the URL for the resource. Once assigned, this value never changes.<br>The only time that a resource does not have an id is when it is being submitted to the server using a create operation.                                                  |
| meta             |          | [Meta](/content/docs/api/fhir/datatypes/meta/index.html)                               | Metadata about the resource<br>Details<br>The metadata about the resource. This is content that is maintained by the infrastructure. Changes to the content might not always be associated with version changes to the resource.                                                                                                        |
| implicitRules    |          | uri                                                                                           | A set of rules under which this content was created<br>Details<br>A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content.                                                                                                            |
| language         |          | code                                                                                          | Language of the resource content<br>Details<br>The base language in which the resource is written. Language is provided to support indexing and accessibility (typically, services such as text to speech use the language tag).                                                                                            |
| text             |          | [Narrative](/content/docs/api/fhir/datatypes/narrative/index.html)                      | Text summary of the resource, for human interpretation<br>Details<br>A human-readable narrative that contains a summary of the resource and can be used to represent the content of the resource to a human. The narrative need not encode all the structured data, but is required to contain sufficient detail to make it "clinically safe" for a human to just read the narrative.                                   |
| contained        |          | Resource\[\]                                                                                  | Contained, inline Resources<br>Details<br>These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, and nor can they have their own independent transaction scope.                                                                                |
| extension        |          | [Extension](/content/docs/api/fhir/datatypes/extension/index.html)\[\]                  | Additional content defined by implementations<br>Details<br>May be used to represent additional information that is not part of the basic definition of the resource.                                                                                                                                                                    |
| modifierExtension |          | [Extension](/content/docs/api/fhir/datatypes/extension/index.html)\[\]                  | Extensions that cannot be ignored<br>Details<br>May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants.                                           |

This resource allows the assertion of linkages between multiple resource instances (generally of the same type) that are referring to the same underlying business objects. For example, multiple [Condition](/content/docs/api/fhir/resources/condition/index.html) records that refer to the same underlying problem/issue for a [Patient](/content/docs/api/fhir/resources/patient/index.html); multiple [AllergyIntolerance](/content/docs/api/fhir/resources/allergyintolerance/index.html) records that refer to the same reaction susceptibility; multiple [Patient](/content/docs/api/fhir/resources/patient/index.html), [Practitioner](/content/docs/api/fhir/resources/practitioner/index.html) and/or [RelatedPerson](/content/docs/api/fhir/resources/relatedperson/index.html) records that refer to the same human being or animal.

FHIR supports a process for sharing electronic records. It is common for multiple records to exist that deal with the same real-world phenomenon. This can result from information being captured by different systems, information being captured within a single system by different users (either deliberately to represent distinct perspectives or accidentally when a new record is created rather than updating an existing record). These multiple records may be referred to as "duplicate" records, but in practice they aren't often actually "duplicate" in that the data represented (and the history of the records) will be at least somewhat distinct.

In some cases, the solution after identifying duplicates is to deprecate one of the records (e.g. by changing the status to "Entered in Error") and to move all relevant information to the surviving record. In other cases, the resource may support the ability to establish a linkage directly between the resources. However, in some cases, both records may need to survive or there might be a desire to have both resources continue to be maintained, perhaps because the resources live on different servers or have different 'owners'. The **Linkage** resource is intended to satisfy this use-case.

The [Person](/content/docs/api/fhir/resources/person/index.html) resource should be used to link a person independent of a specific health-related context. [Linkage](/content/docs/api/fhir/resources/linkage/index.html) can be used for all other use cases.