In the attached file, you will find the data structure that we had imagined (with @Benoit lf) when implementing EPDM in our former company.
We have only implemented part 05_BEM and part 04_AFFAIRE . Knowing that part 04 was only completed by the BE, because only the BE had the EPDM (initially). At therme we had planned to put part of the company under this system.
I'll give you the "raw" file without further explanation, don't hesitate to get back to us if you need more information.
You'll see, this data structure looks a lot like what you describe in your post.