# directed acyclic graph

## directed acyclic graph

A set of nodes connected to one another by lines (edges) in which each connection has a specified direction such that no route that follows the direction of the connections enters a loop (cycle).

#### Notes

* The SNOMED CT subtype hierarchy is a *Directed Acyclic Graph*. SNOMED CT concepts are nodes and subtype relationships are the directed lines that connect them. All subtype relationships lead from a more specific concept to a more general concept, so a cycle would be a logical error (e.g. if "rubella virus" is a type of "virus" and "virus" is a type of "microorganism", then "microorganism" cannot be a type of "rubella virus").

<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: Illustrative Example - Directed Acyclic Graph</p></figcaption></figure>

## Alternatives

* **DAG**

## Related Links

* Wikipedia
  * [Directed Acyclic Graph](http://en.wikipedia.org/wiki/Directed_acyclic_graph)

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