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

Chapter Seventeen. Bringing the Strategy
Together
The preceding three chapters presented many principles and techniques for domain-driven
strategic design. In a large, complex system, you may need to bring several of them to bear on
the same design. How does a large-scale structure coexist with a 
CONTEXT MAP
? Where do the
building blocks fit in? What do you do first? Second? Third? How do you go about devising your
strategy?
[ Team LiB ]

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[ Team LiB ]
Combining Large-Scale Structures and B
OUNDED
C
ONTEXTS
Figure 17.1.
The three basic principles of strategic design (context, distillation, and large-scale structure) are
not substitutes for each other; they are complementary and interact in many ways. For example,
a large-scale structure can exist within one 
BOUNDED CONTEXT,
or it can cut across many of them
and organize the 
CONTEXT MAP
.
The previous examples of 
RESPONSIBILITY LAYERS
were confined to one 
BOUNDED CONTEXT
. This is the
easiest way to explain the idea, and it's a common use of the pattern. In such a simple scenario,
the meanings of layer names are restricted to that 
CONTEXT
, as are the names of model elements
or subsystem interfaces that exist within that 
CONTEXT
.
Figure 17.2. Structuring a model within a single 
BOUNDED CONTEXT

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Such a local structure can be useful in a very complicated but unified model, raising the complexity
ceiling on how much can be maintained in a single 
BOUNDED CONTEXT
.
But on many projects, the greater challenge is to understand how disparate parts fit together.
They may be partitioned into separate 
CONTEXTS
, but what part does each play in the whole
integrated system and how do the parts relate to each other? Then the large-scale structure can
be used to organize the 
CONTEXT MAP
. In this case, the terminology of the structure applies to the
whole project (or at least some clearly bounded part of it).