> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/p/polyhierarchical-classification.md).

# 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="/files/zPbXDIR1atru4HdP7CSS" alt=""><figcaption><p>Figure 1: Hierarchy Illustration - Polyhierarchical Classification</p></figcaption></figure>

## Alternatives

* **Polyhierarchy**

<a href="https://docs.google.com/forms/d/e/1FAIpQLScTmbZIf0UEQwYDkY27EEWBkaiYkHSbR0_9DmFrMLXoQLyL7Q/viewform?usp=pp_url&#x26;entry.1767247133=SNOMED+Glossary&#x26;entry.670899847=polyhierarchical%20classification" class="button primary">Provide Feedback</a>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## 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, and the optional `goal` query parameter:

```
GET https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/p/polyhierarchical-classification.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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.