If you create a code list in a hierarchical reference data set, the code list inherits the hierarchical structure definition from the reference data set. If you create a code list in a reference data set without a hierarchical structure definition, you can configure the structure definition of the code list as hierarchical. After you create a hierarchical code list, you cannot change its structure definition.

For more information about actions that are allowed after code list creation, see Code lists.

For example, you have an Industry Classification reference data set that does not support hierarchical data structures. If you need to create a NAICS code list in the reference data set that supports hierarchies, you configure the structure definition of the code list as hierarchical.