Learning Domain-Driven Design

Chapter 9. Communication Patterns

Chapters 5–8 presented tactical design patterns that define the different ways to implement a system’s components: how to model the business logic and how to organize the internals of a bounded context architecturally. In this chapter, we will step beyond the boundaries of a single component and discuss the patterns for organizing the flow of communication across a system’s elements.

The patterns you will learn about in this chapter facilitate cross-bounded context communication, address the limitations imposed by aggregate design principles, and orchestrate business processes spanning multiple system components.

Model Translation

A bounded context is the boundary of a model—a ubiquitous language. As you learned in Chapter 3, there are different patterns for designing communication across different bounded contexts. Suppose the teams implementing two bounded contexts are communicating effectively and willing to collaborate. In this case, the bounded contexts can be integrated in a partnership: the protocols can be coordinated in an ad hoc manner, and any integration issues can be effectively addressed through communication between the teams. Another cooperation-driven integration method is shared kernel: the teams extract and co-evolve a limited portion of a model; for example, extracting the bounded contexts’ integration contracts into a co-owned repository.

In a customer–supplier relationship, the balance of power tips toward either the upstream ...