# Linkage Concept Hierarchy ## Linkage Concept
Hierarchy106237007 | Linkage concept|
PurposeThis concept is the supertype parent or ancestor of 410662002 | Concept model attribute| , 416698001 | Link assertion| , etc.
Concept Addition Rules

No new subtype children may be added in an extension

See tables below for concept addition rules for the descendants of existing subtype children.

## Concept Model Attributes
Hierarchy410662002 | Concept model attribute|
PurposeThese concepts provide the values for Relationship.typeId and represent the type of a defining relationship.
Examples

Concept Addition RulesAdditional attributes may be added in an extension, where required to support extensions to the SNOMED CT concept model.
Concept Addition Uses CasesExtending the SNOMED CT concept model to allow sufficient definitions to be applied to concepts that are not sufficiently defined in the International Edition.
Additional NotesAny attributes created in extensions need to be carefully managed and documented. Extension attributes may also need to be revised or inactivated to align with future changes to the concept model in the International Edition.
## Link Assertions
Hierarchy416698001 | Link assertion|
PurposeThese concepts represent clinical assertions about relationships between instances of clinical statement in an EHR. For example, they may assert that a particular symptom is caused by something.
International Edition Examples

Concept Addition RulesAdditional subtype children may be added in an extension. However, it is recommended that proposed additions be submitted to the International Edition, unless they are highly specific.
Concept Addition Uses CasesRequirements to support additional types of assertion in clinical records
Provide Feedback --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.snomed.org/snomed-ct-practical-guides/snomed-ct-extension-guide/5-key-steps/5.3-assessing-requests/5.3.2-constraints-on-concept-requests/5.3.2.2-model-metadata-concept-hierarchies/5.3.2.2.3-linkage-concept-hierarchy.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.