Thank you for pointing me to StructureSet, very interesting and could be the way to go forward.
It would not solve all of my requirements though, I will try to explain, giving this table:
The table shows three code lists, having codes for 'things'. A code list covers fully or partially all 'things'.
What I would like to do is just to show all 'things' expressed in their code mappings, thus avoiding using one code list as the reference list where others refer to.
Would this be possible in SDMX and if yes, how?