Your Event Storming Is Not Your Software Design

The Policy That Started the Argument

We were looking at a purple policy between ListingSold and StopListingFee. Read aloud, the flow expressed a simple business expectation: when a listing is sold, the applicable recurring listing fee should stop. The interesting question was where that policy belonged.

If Billing owns it, Billing receives the fact that a listing was sold and determines what that means for its fee model. Listing reports the sale without naming the operation Billing should perform. If Listing owns the coordination, it requests that Billing stop the fee, which means Listing knows that capability exists. A third option is a separate process manager that receives the sale event and coordinates the response.