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Domain-Driven Design: Tackling Complexity in the Heart of Software - A Retrospective 20 Years On

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"Domain-Driven Design: Tackling Complexity in the Heart of Software" revolutionized software development. The book illuminated techniques for designing complex software systems. After Eric Evans published his book, the world of software development could be divided into two phases: before DDD and after DDD.

Why we love the book

A notable strength of the book lies in its capacity to illustrate how the intricacies of the real world can be modeled in code. Evans adeptly unraveled the complexity that frequently hampers software projects, introducing a systematic approach to develop software that accurately represents the intricacies of the business domain.

Evans introduced ground-breaking concepts such as Bounded Context and Ubiquitous Language. He demonstrated how to model real-world entities and interactions in code, emphasizing that while no model is perfect, some are indeed useful.

In subsequent years, concepts building on the foundation of DDD emerged, like Microservice Architecture, which takes the principle of separating applications by Bounded Context. Similarly, Event Storming, which is rooted in the concept of ubiquitous language, aids in requirement gathering. Modern Team Topologies further highlight how industries can allocate developers across teams using the Bounded Context concept introduced by Evans.

Eric's emphasis on the iterative and adaptive nature of software design is noteworthy. He underscored how software systems need to evolve, reflecting a team's growing understanding of the domain. This aligns with the idea of Refactoring, introduced by Martin Fowler around the same period.

Criticism

As an early proponent of Domain-Driven Design, Evans elucidated the core concepts, but several crucial implementation details were missing. Many developers attempting to implement DDD grappled with challenges such as integrating pure models with framework details. Early DDD practitioners also struggled with applying the Dependency Inversion Principle between the Domain Layer and Infrastructure Layer. Robert C. Martin's "Clean Architecture," which addressed this issue with an elegant solution, wasn't introduced until 2012. This initial implementation vagueness coupled with the lack of guidelines in the book occasionally led to a perception of DDD as a theoretical, and not practical, concept.

Additionally, Evans gave considerable attention to tactical patterns, such as Entity and Domain Service. This focus often diverted readers from strategic patterns like ubiquitous language and the evolutionary nature of models. Consequently, many developers perceived DDD more as a collection of tactical patterns rather than as a guiding strategic concept.

While Evans emphasized the Ubiquitous Language as foundational to Domain-Driven Design, the means to formulate such a language was unclear to many developers. The introduction of the term "Event Storming" by Alberto Brandolini a decade after Evans' publication addressed this gap, but the interim saw a decade of frustration for many DDD enthusiasts.

To sum up, "Domain-Driven Design: Tackling Complexity in the Heart of Software" is undoubtedly a seminal work. When released in 2003, the book was avant-garde, setting a new direction for the software industry. However, it took almost another decade for supporting pillars like Clean Architecture and Event Storming to emerge, enabling a comprehensive application of DDD.