Terms- Different Items in a system

Good day Cove team;
A Side Airbag (ITEM) is the unit embedded the bolster of the driver (and passenger) seat. An integral "part" (system? Element?) of this Side Airbag ITEM is the seatbelt pretensioner. Both the ITEM (driver Side Airbag) and the PRETENSIONER share/utilize the same ECU.


Question:

1- Since there is shared activity (interface) would all agree that the PRETENSIONER is a SYSTEM (defined as "a set of components or subsystems") ?
2- Would all also agree that the PRETENSIONER is outside/not include in the boundary of the Side Air Bag?

- Side Airbag (driver)= ITEM

3- Side Airbag (passenger) = ???

4- Pretensioner= ??

5- ECU = ????



Thanks for your help. I'm struggling with with TERM applies to each...

Be well.