The hierarchical structure of parts means that one part can own other parts. Refer to the CYLINDER ASSEMBLY hierarchy shown in figure Multilevel Parts Structure. The parts structure is as follows:

PISTON ASSEMBLY can be thought of as the owner of PISTON, PISTON RING # 1, PISTON RING # 2, and WRIST ASSEMBLY.

We refer to the owning part (PISTON ASSEMBLY) as the parent and the owned parts (PISTON, PISTON RING # 1, PISTON RING # 2, and WRIST ASSEMBLY) as subparts. (Refer to parent/child relationships in the manual Setting Up and Using the HP-DMS Applications.)