How does RRDI relate to the RTC Reportable REST APIs

RRDI: https://jazz.net/library/article/1269

RTC Reportable REST APIs: https://jazz.net/wiki/bin/view/Main/ReportsRESTAPI#workItem_type_com_ibm_team_worki

How does RRDI relate to the RTC Reportable REST APIs?  Is RRDI the same thing but with a query design interface or is RRDI different than the Reportable REST API?  Does one extend the other?  Should I consider RRDI for what I am trying to do (see below)?   If I want to construct or run an existing work item query in my project, will either do the trick?

   For more background and context of what I am trying to do, please refer to this question: https://jazz.net/forum/questions/116952/use-reportable-rest-api-to-obtain-child-work-item-attributes-based-on-parent-and-child-attributes