What are Diagnostic-Related groups (DRG’s), Ambulatory Payment Classification (APC), Outpatient Prospective Payment System (OPPS), Resource Utilization Groups (RUG), and Home Health Resources Groups (HHRG) and how are “codes” like this utilized to try to control cost?

What are Diagnostic-Related groups (DRG’s), Ambulatory Payment Classification (APC), Outpatient Prospective Payment System (OPPS), Resource Utilization Groups (RUG), and Home Health Resources Groups (HHRG) and how are “codes” like this utilized to try to control cost?