Inventory: In the database, when a sales rep sells a vehicle, there will a an update transaction in place which will automatically update the inventory at a particular dealers and subsequently, in the overall groups inventory of vehicles.
I also have a similar DB to create and I've done a few of them in the past.
From reading on different forums, I found that the "proper" way to manage inventory DB was not to update the stock everytime it changed but rather use an stock in/out table to keep track of the quantity.
Basically, when you need to know the stock qty, you run a query calculating how many were purchased, how many were sold, and you get your number.
I've programmed DBs using both systems and can tell you that using an update system can get very messy. The worst case being if the customer finds a way to run a certain transaction twice (and they will...), the inventory numbers don't match anymore and you can't really figure out why.
It would be great to have feedback on this as I have another inventory DB to do and I really want to do it the right way...