A Polyhierarchy is a hierarchy in which each node has one or more parents.
This type of hierarchy can be represented as a graph in which each node has a one
or more directed links to or from other nodes. Since a node in a hierarchy cannot
descendant of itself the resulting graph must not contain cyclic
Relationships. This type of graphs is referred to as a "
Directed Acyclic Graph ".
- Polyhierarchical classification