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

Epilogue: A Cascade of New Insights
That breakthrough got us out of the woods, but it was not the end of the story. The deeper model
opened unexpected opportunities to make the application richer and the design clearer.
Just weeks after the release of the 
Share Pie
version of the software, we noticed another
awkward aspect of the model that was complicating the design. An important 
ENTITY
was missing,
its absence leaving extra responsibilities to be taken up by other objects. Specifically, there were
significant rules governing loan drawdowns, fee payments, and so on, and all this logic was
crammed into various methods on the 
Facility
and 
Loan
. These design problems, which had been
barely noticeable before the 
Share Pie
breakthrough, became obvious with our clearer field of
vision. Now we noticed terms popping up in our discussions that were nowhere to be found in the
model—terms such as "transaction" (meaning a financial transaction)—that we started to realize
were being implied by all those complicated methods.
Following a process similar to the one described earlier (although, thankfully, under much less
time pressure) led to yet another round of insights and a still deeper model. This new model made
those implicit concepts explicit, as kinds of 
Transactions
, and at the same time simplified the
Positions
(an abstraction including the 
Facility
and 
Loan
). It became easy to define the diverse
transactions we had, along with their rules, negotiating procedures, and approval processes, and
all in relatively self-explanatory code.
Figure 8.9. Another model break-through that followed several weeks
later. Constraints on Transactions could be expressed with easy
precision.
As is often the case after a real breakthrough to a deep model, the clarity and simplicity of the
new design, combined with the enhanced communication based on the new 
UBIQUITOUS LANGUAGE
,
had led to yet another modeling breakthrough.
Our pace of development was accelerating at a stage where most projects are beginning to bog
down in the mass and complexity of what has already been built.

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[ Team LiB ]

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[ Team LiB ]