A hierarchical view of that differs from the and enables an alternative way to locate and view part or all of the concept of .

enables navigation hierarchies to be specified using either:
- an ordered association reference set in which the display order of nodes can be specified; or
- an association reference set which the display order is not specified.
The links in a navigation hierarchy do not contribute in any way to the semantic definitions of the linked .
A navigation hierarchy may include which are created to represent nodes in the hierarchy exist only to organize the hierarchy and cannot be selected for data entry.
A navigation hierarchy may be limited to a subset of relevant to a particular use case.
Many different navigation hierarchies can be created, each specifying a structure that meets the needs of a particular use case.

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