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

1.
Large projects may bog down because the coordination over-head exceeds their abilities.
2.
Applications with specialized requirements may have to use models that don't fully satisfy
their needs, forcing them to put behavior elsewhere.
3.
Conversely, attempting to satisfy everyone with a single model may lead to complex options
that make the model difficult to use.
4.
What's more, model divergences are as likely to come from political fragmentation and differing
management priorities as from technical concerns. And the emergence of different models can be
a result of team organization and development process. So even when no technical factor prevents
full integration, the project may still face multiple models.
Given that it isn't feasible to maintain a unified model for an entire enterprise, we don't have to
leave ourselves at the mercy of events. Through a combination of proactive decisions about what
should be unified and pragmatic recognition of what is not unified, we can create a clear, shared
picture of the situation. With that in hand, we can set about making sure that the parts we want to
unify stay that way, and the parts that are not unified don't cause confusion or corruption.
We need a way to mark the boundaries and relationships between different models. We need to
choose our strategy consciously and then follow our strategy consistently.
This chapter lays out techniques for recognizing, communicating, and choosing the limits of a
model and its relationships to others. It all starts with mapping the current terrain of the project. A
BOUNDED CONTEXT
defines the range of applicability of each model, while a 
CONTEXT MAP
gives a
global overview of the project's contexts and the relationships between them. This reduction of
ambiguity will, in and of itself, change the way things happen on the project, but it isn't necessarily
enough. Once we have a 
CONTEXT BOUNDED
, a process of 
CONTINUOUS INTEGRATION
will keep the
model unified.
Then, starting from this stable situation, we can start to migrate toward more effective strategies
for 
BOUNDING CONTEXTS
and relating them, ranging from closely allied contexts with 
SHARED
KERNELS
to loosely coupled models that go their 
SEPARATE WAYS
.