Difference between Contraint PickList and Hierearchial Pickl ist

Constraint Picklist:While configuring Constraint PickList, we use two different picklist for parent and child field and both picklist should based on PickLIst Genericbusiness component

Hierarchial Picklist:while for hierarchical, both fields(parent and child) uses the same picklist and picklist is based on PickList Hierarchical Business component.E-x Country--State-District.
To Create Hierarchial picklist refer to:http://blogs.oracle.com/siebelessentials/2008/11/hierarchical_picklists_unveile.html