We have recently written a short article describing several methods of accomplishing a popular business model design task, which generated support calls in the past. Some things may already be known to you (e.g., the fact that in XAF you can control many things at the data model class and Controller level), but others are worth repeating, and I hope you will find this article helpful:
As always, I look forward to hearing your feedback in comments to this blog post. Thanks in advance.