In Part I, we discussed the “what” and “why” of software: you learned to analyze busi‐ ness domains, identify subdomains and their strategic value, and turn the knowledge of business domains into the design of bounded contexts—software components implementing different models of the business domain.

In this part of the book, we will turn from strategy to tactics: the “how” of software design:

• In Chapters 5 through 7, you will learn business logic implementation patterns that allow the code to speak the ubiquitous language of its bounded context. Chapter 5 introduces two patterns that accommodate a relatively simple business logic: transaction script and active record. Chapter 6 moves to more challenging cases and presents the domain model pattern: DDD’s way of implementing com‐ plex business logic. In Chapter 7, you will learn to expand the domain model pat‐ tern by modeling the dimension of time.

• In Chapter 8, we will explore the different ways to organize a bounded context’s architecture: the layered architecture, ports & adapters, and CQRS patterns. You will learn the essence of each architectural pattern and in which cases each pat‐ tern should be used.

• Chapter 9 will discuss technical concerns and implementation strategies for orchestrating the interactions among components of a system. You will learn pat‐ terns supporting the implementation of bounded context integration patterns, how to implement reliable publishing of messages, and patterns for defining complex, cross-component workflows.

CHAPTER 5