Mats Helander has written an excellent article on how to manage your domain model with some intelligent design trade-offs.  It’s a lengthy article that even manages to introduce AOP as well.  If you start reading it and wonder where it’s going, just carry on reading…it is written in an evolutionary style.  Nice article, Mats! UPDATE: I have written the Java equivalent of the listing in Mats’ article and attached it.  The AOP part uses SpringFramework 2.5 and AspectJ.