Domain-Driven Design: Tackling Complexity in the Heart of Software

Delivery
, as shown in Figure 15.3.
Figure 15.3. Reliable delivery in adherence with customer requirements
is the core goal of this project.

---

For the most part, classes have just moved into the new package, but there have been a few
changes to the model itself.
First, the 
Customer Agreement
now constrains the 
Handling Step
. This is typical of the
insights that tend to arise as the team segregates the 
CORE
. As attention is focused on effective,
correct delivery, it becomes clear that the delivery constraints in the 
Customer Agreement
are
fundamental and should be 
explicit
in the model.
The other change is more pragmatic. In the refactored model, the 
Customer Agreement
is
attached directly to the 
Cargo
, rather than requiring a navigation through the 
Customer
. (It will
have to be attached when the 
Cargo
is booked, just as the 
Customer
is.) At actual delivery time,
the 
Customer
is not as relevant to operations as the agreement itself. In the other model, the
correct 
Customer
had to be found, according to the role it played in the shipment, and then
queried for its 
Customer Agreement
. This interaction would clog up every story you set out to
tell about the model. The new association makes the most important scenarios as simple and
direct as possible. Now it becomes easy to pull the 
Customer
out of the 
CORE
altogether.
And what about pulling 
Customer
out, anyway? The focus is on fulfilling the 
Customer's

---

requirements, so at first