Hi Tobias,
I too do not see the semantic grouping option in a transformation that originates from an MPRO.
Couldn't find the reason anywhere, but it maybe due to how I guess the Sem. grouping feature works. By the way, all of the below is just a (hopefully educated) guess.
Essentially when you use Sem.Grp, it adds a GROUP BY clause into the select statement that is fired on the source InfoProvider. So the DB (or App server) needs to figure out how many records exist for the each combination of the semantic group characteristic, and then batch them up and send them in each data packet.
Now as an MPRO doesn't contain data and is itself a union of multiple InfoProviders (with potentially differing granularities and field mappings), figuring out the grouping combinations and record counts for each group can be a major challenge, which is why Sem grouping isn't allowed.
Regards,
Suhas