I find I can tease out better assumptions and requirements by starting with the model. You immediately need answers to vital questions (more than one address,

I find I can tease out better assumptions and requirements by starting with the model. You immediately need answers to vital questions (more than one address, how are items related, etc). It's so valuable, I can't imagine starting any contentious project without doing that. If my assumptions are wrong, I go back the model and change that and reflow the changes back through the rest of product. It's again usually pretty easy and mechanical to make those changes once the model is again correct.