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

Shipping Project's Strategy
Insurance Project's Strategy
Advantages
G
ENERIC
model decoupled from
C
ORE
.
C
ORE
model mature, so
resources could be diverted
without stunting it.
Knew exactly what they needed.
Critical support functionality for
international scheduling.
Programmer on short-term
contract used for 
GENERIC
task.
Disadvantage
Advantage
G
ENERIC
model decoupled from 
CORE
.
Disadvantages
C
ORE
model undeveloped, so attention to other
issues continued this neglect.
Unknown requirements led to attempt at full
generality, where simpler North America-specific
conversion might have sufficed.
Long-term programmers were assigned who could
have been repositories of domain knowledge.

---

Diverted top programmer from
core.
We technical people tend to enjoy definable problems like time zone conversion, and we can easily
justify spending our time on them. But a disciplined look at priorities usually points to the 
CORE
DOMAIN
.
Generic Doesn't Mean Reusable
Note that while I have emphasized the generic quality of these subdomains, I have not mentioned
the reusability of code. Off-the-shelf solutions may or may not make sense for a particular
situation, but assuming that you are implementing the code yourself, in-house or outsourced, you
should specifically not concern yourself with the reusability of that code. This would go against the
basic motivation of distillation: that you should be applying as much of your effort to the 
CORE
DOMAIN
as possible and investing in supporting 
GENERIC SUB-DOMAINS
only as necessary.
Reuse does happen, but not always code reuse. The model reuse is often a better level of reuse,
as when you use a published design or model. And if you have to create your own model, it may
well be valuable in a later related project. But while the concept of such a model may be applicable
to many situations, you do not have to develop the model in its full generality. You can model and
implement only the part you need for your business.
Though you should seldom design for reusability, you must be strict about keeping within the
generic concept.
Introducing industry-specific model elements will have two costs. First, it will
impede future development. Although you need only a small part of the subdomain model now,
your needs will grow. By introducing anything to the design that is not part of the concept, you
make it much more difficult to expand the system cleanly without completely rebuilding the older