I realize I've been asking you a lot of question lately and will probably get throttled which is fair enough :). But if you've got the time and feel like it: Say some products require reservation on existing stock but some don't. 1/7 So, an order must be accepted or not based on the specific product and stock levels. There's a whole domain around orders and another around stock. They naturally form boundaries for two services: Orders & Stock. Yet the last stage of accepting an order takes input from both. 2/7