In a Hierarchy Processor transformation, a data source identifies the input group or incoming array that populates the primitive child fields of the output group or field.
When the output is relational, the data source for the output groups is always the input group or an incoming field. For example, you add an array to the output group. If you add single occurring children, the data source for the output group is the input group. If you add all descendants, the data source for each output group is an incoming field array.