Tim,
I actually just found that document, thanks.
The models don't change in terms of the hierarchy, but the information I need to know about them is...unknown. As we test and develop we're finding more critical peices of information that are model- or series-specific. For instance (most of our products are pumps, btw), one series has a clearance dimension between the impeller and case that is critical to performance, but this clearance isn't even a feature of most of our designs. In order to make the data useful, I have to track that clearance for each test done on that series of products. Because of this I will need to be able to reliably and easily adjust the way my application responds to different series and models, which sounded like plugins to me.