# polyhierarchical classification

## polyhierarchical classification

A hierarchy in which each node has one or more parents.

#### Notes

* The subtype relationships of SNOMED CT create a *polyhierarchical classification*.
* A *polyhierarchical classification* can be represented as a graph in which each node has a one or more directed links to or from other nodes.
* A node in a *polyhierarchical classification* cannot be a descendant of itself, which means the hierarchy must not contain cyclic relationships. This type of hierarchy is therefore known as a directed acyclic graph.

#### Examples

* The diagram below shows a polyhierarchy. Each node has one or more parent node so there can be multiple paths from a node to the top (or root) of the hierarchy.\
  For example from node V the paths include the following:
  * V→N→F→B→A
  * V→N→F→C→A
  * V→G→C→A

<figure><img src="https://1017548453-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FP21QucCX9Y41nBQt50ad%2Fuploads%2Fgit-blob-c45fd9213c87bdd5ceac785858ccb83caff84963%2F82880191.png?alt=media" alt=""><figcaption><p>Figure 1: Hierarchy Illustration - Polyhierarchical Classification</p></figcaption></figure>

## Alternatives

* **Polyhierarchy**

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