Wow, that definitely did help! I've gotta say though that the way Filemaker makes connections still feels like some kind of magic.
Anyway, all that to say I've extened your example with unqiue ids to cause RemoteInventory::BatteryInstalled to fire a OnObjectExit script that create a back-reference to itself in BatteryInventory. I'd ask more questions about in the direction of what I'm trying achieve, but by the end of all that you'd pretty much have completely finished my little project for me!
I'm going to try and see if I can find something for people who are coming to Filemaker from a SQL background.
edit -- I meant to give you the Best Answer tick! Is there any way to change it?