I think that I'm being thick - it's a little while since I've needed to create a new database and I've lost a few skills! I have databases with portals and related products but this one stumped me (it's probably very simple).
I'm creating a product database with all the usual stuff, code numbers, descriptions, components, costings etc. These are items that we make. I've hit a mental blank - a number of the components that combine to make a product we also make. For instance Product A requires packaging element B & C; both of which we make and sell individually and separately. These need to be headline items because they have components themselves - it sort of goes in a loop. As an example you have a car which is a part number; it includes an engine which is also a part number. You can buy the car (including an engine) or just an engine (without the car, as a replacement). Tyres might have been a better example!
What's my structure?