A hierarchy in which each node has one or more parents.
- 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.
- 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:
Figure 1: Hierarchy Illustration - Polyhierarchical Classification