Types of parent-child relationships in STEP

Does anyone have a complete hierarchy of all possible parent-child relationships that can exist in a STEP file, and how these relationships are translated when using OCC? I am using OCC to parse STEP files, analyse the assembly structure and visualise the parts/sub-parts/shapes. However, I have found that for some of my STEP test cases, there are more nodes in the assembly graph that there are instances of NEXT_ASSEMBLY_USAGE_OCCURRENCE in the file.

I would rephrase my question as "whole-part" rather than "parent-child", but "part" has a specific meaning here! However, that's what I mean mereologically.

Some of the non-NAUO relationships are shape-(sub-shape) relationships, which I can account for, but some aren't. There is some information in the user guides here, but I was wondering whether anyone has any more specific, detailed info in terms of the logic used to construct the graph. Details: Windows 10, using OCC via PythonOCC.