Understanding Joint Group Data in Metahuman DNA Calibration

Hi,

I am developing Maya tools around DNA Calibration tools to create Custom Metahumans on meshes that would not work in Mesh to Metahuman. I’m trying to wrap my head around Behavior layer data, looking at the DNA file as JSON, reading the white paper on rig logic and documentation.

I have learned a lot but am still unclear on the exact nature of
input indices (contains expression index and other data?),
output indices (same question as input indices)
How to find specific data in it? Do I look at JointRowCount and JointColumnCount to help determine where the value for a particular expression or control resides etc?

I have some workarounds to get most of the data I need but do need to figure out jointgroup values at the very least so that I can save the resulting updates to control triggered joint positions.

jointgroup values (I think based on y=kx or is it y=kx+b?
my understanding is that:
y is the resulting stored value
k is the delta (triggered transform - neutral transform) * x which is the control value, in the case of stored values, always 1.
b would be adding the neutral value again for the actual scene transform value I think

Any help in clarifying this data would be appreciated.

Thank you.