Domain-driven Design: Tackling Complexity in the Heart of Software Eric Evans
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A detailed look at domain-driven design in software development, including basic implementation and a handful of advantages and disadvantages of its use. Yet the most significant complexity of many applications is not technical. When this domain complexity is not dealt with in the design, it won't matter that the infrastructural technology is well-conceived. A successful design must systematically deal with this central aspect of the software.
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I've tried best practices in design and development process as they have emerged from the leaders in the object-oriented development community. A feature common to the successes was a rich domain model that evolved through iterations of design and became part of the fabric of the project. This book intertwines design and development practice and illustrates how domain-driven design and agile development reinforce each other. A sophisticated approach to domain modeling within the context of an agile development process will accelerate development. The interrelationship of process with domain development makes this approach more practical than any treatment of 'pure' design in a vacuum.
Agile Software Development
When complexity gets out of hand, the software can no longer be understood well enough to be easily changed or extended. By contrast, a good design can make opportunities out of those complex features. XP recognizes the importance of design decisions, but strongly resists upfront design. Instead, it puts an admirable effort into increasing communication, and increasing the project's ability to change course rapidly. Extreme Programming (XP), conceived by Kent Beck, Ward Cunningham and others Beck2000, is the most prominent of the agile processes and the one I have worked with most.
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Eric Evans is the founder of Domain Language, a consulting group dedicated to helping companies build evolving software deeply connected to their businesses. Since the 1980s, Eric has worked as a designer and programmer on large object-oriented systems in several complex business and technical domains. Throughout the book, discussions are illustrated with realistic examples, drawn from actual projects, rather than oversimplified 'toy' problems. Throughout the book, discussions are illustrated with realistic examples, drawn from actual projects, rather than oversimplified "toy" problems.
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A skimmer who already has some grasp of a topic should be able to pick up the main points by reading headings and bolded text. A very advanced reader may want to skim Parts I and II, and will probably be most interested in Parts III and IV. Get Mark Richards’s Software Architecture Patterns ebook to better understand how to design components—and how they should interact. “If you don’t think you aregetting value from your investment in object-oriented programming,this book will tell you what you’ve forgotten to do. O’Reilly members get unlimited access to books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
Although it has never been clearly formulated, a philosophy has developed as an undercurrent in the object community, which I call "domain-driven design". Should you use Domain-Driven Design within your software development life cycle? If you have a domain expert on the team and want a design that promotes communication and flexibility on a project that isn't overly technical, Domain-Driven Design would be a great option for you!
Intertwining system design and development practice, this book incorporates numerous examples based on actual projects to illustrate the application of domain-driven design to real-world software modeling and development. Itoffers readers a systematic approach to domain-driven design,presenting an extensive set of design best practices,experience-based techniques, and fundamental principles thatfacilitate the development of software projects facing complexdomains. Intertwining design and development practice, this bookincorporates numerous examples based on actual projects toillustrate the application of domain-driven design to real-worldsoftware development. Throughout the book, discussions are illustrated not with over-simplified, “” problems, but with realistic examples adapted from actual projects. Throughout the book, discussions are illustrated not with over-simplified, "" problems, but with realistic examples adapted from actual projects. Unfortunately, not all projects that start with this intention manage to arrive at this virtuous cycle.
When people learn design techniques, they feel excited by the possibilities, but then the messy realities of a real project descend on them. They don't see how to fit the new design ideas with the technology they must use. Or they don't know when to worry about a particular design aspect and when to let go in the interest of time.
While it is possible to talk with other team members about the application of a design principle in the abstract, it is more natural to talk about the things we do together. So, while this is a design book, I'm going to barge right across that artificial boundary when I need to. Leading software designers have recognized domain modeling and design as critical topics for at least twenty years, yet surprisingly little has been written about what needs to be done or how to do it. Although it has never been clearly formulated, a philosophy has developed as an undercurrent in the object community, which I call 'domain-driven design'.
A domain-driven design is a difficult technical challenge that can pay off big, opening opportunities just at the stage when most software projects begin to ossify into legacy. But the main point of this section is on the kind of decisions that keep the model and implementation aligned with each other, reinforcing each other's effectiveness. Careful crafting at this small scale gives developers a steady platform to apply the modeling approaches of Parts III and IV. Expanding on our previous article that covered Object-Oriented Analysis and Design (OOAD), today's article will explore domain-driven design (DDD). DDD is a software development approach that uses and builds upon OOAD principles and ideas, so it's the next logical topic for us to dive into. Of course many things can put a project off course, bureaucracy, unclear objectives, lack of resources, to name a few, but it is the approach to design that largely determines how complex software can become.
Throughout this article, we'll examine what domain-driven design is, how it is commonly implemented in modern development life cycles, and consider a few potential advantages and disadvantages of using DDD in your own projects. Much of the book is written as a set of 'patterns.' The reader should be able to fully understand the material without concern about this device, but those who are interested in the style and format of the patterns can read Appendix A. This book is not specific to a particular methodology, but it is oriented toward the new family of 'Agile Development Processes'. Specifically, it assumes a couple of process practices are in place on the project. These two practices are prerequisites for applying the approach in this book.
This book provides a framework for making design decisions and a technical vocabulary for discussing domain design. It is a synthesis of widely accepted best practices along with my own insights and experiences. Projects facing complex domains can use this framework to approach domain-driven design systematically. But I believe that these two issues are inextricable if design concepts are to be put into successful practice and not dry up into academic discussion.
Repeated iteration produced no improvement in the code, due to uneven skill-level among developers with no clear understanding of the particular kind of rigor needed. As months rolled by, development work became mired in complexity and the team lost its cohesive vision of the system. After years of effort, the project did produce modest, useful software, but had given up the early ambitions along with the model focus. The systematic approach to design will help them in leading teams down this path. But despite its obviousimportance, there are few practical resources that explain how toincorporate effective domain modeling into the software developmentprocess. This book is primarily written for developers of object-oriented software.
But, for those more technical projects, you might want to consider a different software development life cycle, like OOAD or an Iterative Model. Project managers should be interested in the emphasis on making a team more effective and more focused on designing software meaningful to business experts and users. And, since, strategic design decisions are interrelated with team organization and work styles, these design decisions necessarily involve the leadership of the project, and have a major impact on the project's trajectory. Three projects stand out in my memory as vivid examples of the dramatic effect domain design practice has on development results. Although all three delivered useful software, only one achieved its ambitious objectives and delivered complex software that continued to evolve to meet ongoing needs of the organization.
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