Summary
Another use-case is if you have a nested input, like our SALESORDERs with its SALESITEMs. Now we want to join those tables. Very simple. They already form a structure, so the child belongs to its parent already.
All we have to do is "unnest" the child this effectively joining those.
Since ORDERITEMs and CUSTOMERS are both tables at the same level, we will build a Cartesian product of the two. Who cares, ITEMs times ONE customer row is still correct.
So the endresult will look like as if we would have joined the SALESORDERs table to the SALESITEMs table right away instead of building the NRDM model.