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

Deep Models Distill
Distillation does not operate only on the gross level of separating parts of the domain away from
the 
CORE
. It also means refining those subdomains, especially the 
CORE DOMAIN
, through
continuously refactoring toward deeper insight, driving toward a deep model and supple design.
The goal is a design that makes the model obvious, a model that expresses the domain simply. A
deep model distills the most essential aspects of a domain into simple elements that can be
combined to solve the important problems of the application.
Although a breakthrough to a deep model provides value anywhere it happens, it is in
the 
CORE DOMAIN
 that it can change the trajectory of an entire project.
[ Team LiB ]

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[ Team LiB ]
Choosing Refactoring Targets
When you encounter a large system that is poorly factored, where do you start? In the XP
community, the answer tends to be either one of these:
Just start anywhere, because it all has to be refactored.
1.
Start wherever it is hurting. I'll refactor what I need to in order to get my specific task done.
2.
I don't hold with either of these. The first is impractical except in a few projects staffed entirely
with top programmers. The second tends to pick around the edges, treating symptoms and
ignoring root causes, shying away from the worst tangles. Eventually the code becomes harder
and harder to refactor.
So, if you can't do it all, and you can't be pain-driven, what do you do?
In a pain-driven refactoring, you look to see if the root involves the 
CORE DOMAIN
or the
relationship of the 
CORE
to a supporting element. If it does, you bite the bullet and fix that
first.
1.
When you have the luxury of refactoring freely, you focus first on better factoring of the 
CORE
DOMAIN
, on improving the segregation of the 
CORE
, and on purifying supporting subdomains
to be 
GENERIC
.
2.
This is how to get the most bang for your refactoring buck.
[ Team LiB ]

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[ Team LiB ]