Master Domain-Driven Design with Eric Evans' Book: Ebook PDF Download and Tips
Domain-Driven Design: Tackling Complexity in the Heart of Software by Eric Evans
If you are a software developer, system analyst, or designer who wants to learn how to tackle complex domains and create high-quality software systems, you might want to read Domain-Driven Design: Tackling Complexity in the Heart of Software by Eric Evans.
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This book, published in 2004, is considered a classic in the field of software design. It offers a systematic approach to domain-driven design, presenting an extensive set of design best practices, experience-based techniques, and fundamental principles that facilitate the development of software projects facing complex domains.
In this article, we will give you an overview of what domain-driven design is, how to apply it in practice, what are the key takeaways from the book, and how to download the ebook pdf version of the book.
What is domain-driven design?
Domain-driven design (DDD) is a way of thinking and designing software systems that focuses on the domain, which is the problem space that the system aims to solve.
The domain is composed of various concepts, rules, processes, and behaviors that define the business logic and value of the system. For example, if you are building an online shopping system, some of the domain concepts might be products, customers, orders, payments, etc.
DDD advocates that software developers should collaborate closely with domain experts, who are people who have deep knowledge and experience in the domain. By doing so, developers can learn the language and nuances of the domain, and use it to create a domain model, which is a representation of the domain in code.
The domain model should be rich and expressive, capturing both the static structure and dynamic behavior of the domain. It should also be consistent and coherent, reflecting a shared understanding among developers and domain experts. The domain model should drive the design and implementation of the software system, ensuring that it meets the needs and expectations of the users.
The benefits of DDD are that it helps developers to:
Understand and communicate better with domain experts and users
Create software systems that are aligned with business goals and values
Reduce complexity and ambiguity by focusing on what matters most
Increase quality and maintainability by following best practices and principles
Adapt and evolve with changing requirements and feedback
How to apply domain-driven design in practice?
The book by Eric Evans provides a comprehensive guide on how to apply DDD in practice. It covers four main aspects:
Model-driven design
Refactoring
Strategic design
Supplementary techniques
We will briefly summarize each aspect below.
Model-driven design
Model-driven design is the core of DDD. It is about creating a domain model that reflects the domain logic and rules, and using it to drive the design and implementation of the software system.
The book introduces a set of basic building blocks for model-driven design, such as:
Entities: Objects that have a unique identity and a lifecycle, such as Customer, Order, Product, etc.
Value objects: Objects that have no identity and are immutable, such as Money, Address, Date, etc.
Services: Objects that perform operations that do not belong to any entity or value object, such as PaymentService, EmailService, etc.
Repositories: Objects that provide access to entities and value objects, such as CustomerRepository, OrderRepository, etc.
Factories: Objects that create entities and value objects, such as CustomerFactory, OrderFactory, etc.
Aggregates: Clusters of entities and value objects that form a consistency boundary, such as Order and its line items, Customer and its addresses, etc.
The book also explains how to use these building blocks to create a ubiquitous language, which is a common and consistent vocabulary that developers and domain experts use to communicate about the domain. The ubiquitous language should be reflected in the code, the documentation, and the user interface of the software system.
Refactoring
Refactoring is the process of improving and evolving the domain model and the code over time. It is essential for DDD, as the domain is not static but dynamic, and the understanding of the domain can change as developers learn more from domain experts and users.
The book provides a number of modeling principles that can guide refactoring decisions, such as:
Intention-revealing interfaces: The interfaces of entities, value objects, services, repositories, factories, and aggregates should reveal their purpose and behavior clearly and explicitly.
Side-effect-free functions: The methods of value objects should not have any side effects or change any state. They should only return new value objects or perform calculations.
Assertions: The code should include assertions that check the validity and consistency of the domain model and its invariants.
Conceptual contours: The code should be organized according to the natural boundaries and relationships of the domain concepts, not according to technical or implementation details.
Standalone classes: The classes should be designed to be independent and reusable, not coupled or dependent on other classes or frameworks.
Closure of operations: The operations on entities and value objects should be complete and consistent within themselves, not relying on external services or repositories.
The book also describes some refactoring techniques that help to improve the domain model and the code quality, such as:
Supple design: A design that is flexible and expressive, allowing developers to make changes easily and safely.
Specification pattern: A pattern that encapsulates business rules and criteria into reusable objects that can be composed and applied to entities and value objects.
Lazy loading: A technique that delays the loading of data from repositories until it is needed by entities or value objects.
Caching: A technique that stores data in memory or disk for faster access by entities or value objects.
Concurrency control: A technique that prevents data corruption or inconsistency when multiple users or processes access or modify the same data concurrently.
Strategic design
Strategic design is about dealing with large-scale systems and complex domains. It is about defining the scope and boundaries of the domain model, identifying the core domain and subdomains, and applying patterns to integrate them.
The book introduces three main principles for strategic design:
Bounded context: A boundary within which a specific domain model applies. A bounded context defines a consistent language and meaning for the domain concepts within it. Different bounded contexts can have different models for the same concept. For example, in an online shopping system, there can be different bounded contexts for order management, inventory management, payment processing, etc.
Distillation
Distillation is the process of identifying and extracting the core domain and subdomains from a complex domain. The core domain is the most essential and valuable part of the domain, where the competitive advantage and innovation lie. The subdomains are the supporting or generic parts of the domain, where the standard or common solutions apply.
Distillation helps to prioritize and focus on the core domain, and to separate and isolate it from the subdomains. It also helps to reduce complexity and noise by eliminating or simplifying irrelevant or distracting aspects of the domain.
The book suggests some techniques for distillation, such as:
Core domain: A subset of the domain model that captures the core concepts and rules of the domain. The core domain should be refined and protected from changes or influences from other parts of the system.
Generic subdomain: A subset of the domain model that applies common or standard solutions to a part of the domain. The generic subdomain can be reused or replaced by existing frameworks or libraries.
Supporting subdomain: A subset of the domain model that provides supporting or auxiliary functionality to the core domain. The supporting subdomain can be delegated or outsourced to other teams or systems.
Domain vision statement: A concise and clear statement that describes the purpose and scope of the core domain and its subdomains.
Highlighted core: A visual representation of the core domain and its subdomains, using colors or shapes to emphasize their importance and relationships.
Patterns
Patterns are reusable solutions to common problems in software design. The book presents a set of patterns that can help to integrate different bounded contexts and subdomains, such as:
Shared kernel: A small subset of the domain model that is shared and agreed upon by two bounded contexts. The shared kernel defines a common language and contract for the integration.
Customer/supplier: A relationship between two bounded contexts where one acts as a customer and the other as a supplier. The customer defines the requirements and expectations for the integration, and the supplier delivers the service or functionality.
Conformist: A relationship between two bounded contexts where one conforms to the model and language of the other. The conformist accepts the integration as it is, without trying to influence or change it.
Anticorruption layer: A layer between two bounded contexts that translates and adapts the model and language of one into the model and language of the other. The anticorruption layer protects one bounded context from being corrupted or influenced by another.
Separate ways: A relationship between two bounded contexts where they are not integrated at all. They operate independently and autonomously, without any communication or dependency.
Open host service: A service provided by one bounded context that is open and accessible to other bounded contexts. The service defines a protocol and a contract that specify how to communicate and interact with it.
Published language: A language defined by one bounded context that is published and available to other bounded contexts. The language can be a data schema, a message format, an API specification, etc.
What are the key takeaways from the book?
The book by Eric Evans is a comprehensive and in-depth guide on how to apply domain-driven design in practice. It provides a wealth of knowledge and experience on how to create software systems that are aligned with business goals and values, and that can adapt and evolve with changing requirements and feedback.
Some of the key takeaways from the book are:
The domain is the problem space that the software system aims to solve. It is composed of various concepts, rules, processes, and behaviors that define the business logic and value of the system.
Domain-driven design is a way of thinking and designing software systems that focuses on the domain, and uses it to drive the design and implementation of the software system.
Software developers should collaborate closely with domain experts, who are people who have deep knowledge and experience in the domain. They should learn the language and nuances of the domain, and use it to create a domain model, which is a representation of the domain in code.
The domain model should be rich and expressive, capturing both the static structure and dynamic behavior of the domain. It should also be consistent and coherent, reflecting a shared understanding among developers and domain experts.
The domain model should be refined and evolved over time, as the understanding of the domain changes or improves. Refactoring is the process of improving and evolving the domain model and the code.
The domain model should be scoped and bounded by defining bounded contexts, which are boundaries within which a specific domain model applies. Different bounded contexts can have different models for the same concept.
The domain model should be distilled by identifying and extracting the core domain and subdomains from a complex domain. The core domain is the most essential and valuable part of the domain, where the competitive advantage and innovation lie. The subdomains are the supporting or generic parts of the domain, where the standard or common solutions apply.
The domain model should be integrated by applying patterns that can help to communicate and interact with different bounded contexts and subdomains. Patterns are reusable solutions to common problems in software design.
How to download the ebook pdf version of the book?
If you are interested in reading the book by Eric Evans, you might want to download the ebook pdf version of the book. There are several ways to do that, such as:
Buying the ebook pdf version from the official website of the publisher, Addison-Wesley Professional. You can find it here.
Buying the ebook pdf version from other online platforms, such as Amazon, Google Play Books, Apple Books, etc. You can search for them on your preferred platform.
Downloading the ebook pdf version from free or pirated sources, such as GitHub, Torrent, etc. However, we do not recommend this option, as it is illegal and unethical. You should respect the author's rights and efforts, and support him by buying his book.
Conclusion
In this article, we have given you an overview of what domain-driven design is, how to apply it in practice, what are the key takeaways from the book by Eric Evans, and how to download the ebook pdf version of the book.
We hope that you have found this article useful and informative. If you want to learn more about domain-driven design, we highly recommend that you read the book by Eric Evans. It is a classic and a must-read for any software developer who wants to create high-quality software systems that are aligned with business goals and values.
Thank you for reading this article. If you have any questions or feedback, please feel free to leave a comment below. We would love to hear from you.
FAQs
Here are some frequently asked questions and answers about the book and domain-driven design.
Who is Eric Evans?
Eric Evans is a software developer, consultant, speaker, and author. He is the founder of Domain Language, a consulting company that specializes in domain-driven design. He is also the author of Domain-Driven Design: Tackling Complexity in the Heart of Software, which is considered a classic in the field of software design.
What is Domain Language?
Domain Language is a consulting company that helps software teams to apply domain-driven design in their projects. They offer training, coaching, mentoring, and consulting services. They also host events and workshops on domain-driven design. You can find more information about them on their website: https://domainlanguage.com/.
What are some other books or resources on domain-driven design?
There are many other books or resources on domain-driven design that you can read or watch, such as:
Implementing Domain-Driven Design by Vaughn Vernon: A practical guide on how to implement domain-driven design using examples and code snippets.
Domain-Driven Design Distilled by Vaughn Vernon: A concise and accessible introduction to domain-driven design for beginners.
Domain-Driven Design in PHP by Carlos Buenosvinos, Christian Soronellas, and Keyvan Akbary: A hands-on guide on how to apply domain-driven design in PHP projects using real-world scenarios.
Domain-Driven Design: The First 15 Years edited by Alberto Brandolini et al.: A collection of essays and interviews from various experts and practitioners on domain-driven design.
DDD Community
: A website that hosts various resources and events on domain-driven design, such as articles, videos, podcasts, conferences, meetups, etc. You can find it here: https://dddcommunity.org/.
DDD Europe: A conference that focuses on domain-driven design and related topics, such as software architecture, design patterns, event sourcing, microservices, etc. You can find more information about it here: https://dddeurope.com/.
What are some examples of domain-driven design in action?
There are many examples of domain-driven design in action in various domains and industries, such as:
eBay: An online marketplace that uses domain-driven design to model and implement its core domain of online trading and commerce.
Spotify: A music streaming service that uses domain-driven design to model and implement its core domain of music discovery and consumption.
Zalando: An online fashion retailer that uses domain-driven design to model and implement its core domain of fashion e-commerce and personalization.
ING: A banking and financial services company that uses domain-driven design to model and implement its core domain of banking and finance.
Netflix: A video streaming service that uses domain-driven design to model and implement its core domain of video entertainment and recommendation.
How can I learn and practice domain-driven design?
The best way to learn and practice domain-driven design is to apply it to real-world projects and problems. You can start by reading the book by Eric Evans or other books or resources on domain-driven design. Then, you can try to identify and model the domain of a project or problem that you are working on or interested in. You can also join or create a study group or a community of practice with other developers who are interested in domain-driven design. You can share your ideas and feedback, learn from each other's experiences, and collaborate on projects or challenges.
What are the challenges or pitfalls of domain-driven design?
Domain-driven design is not a silver bullet or a magic solution. It has its own challenges and pitfalls, such as:
Finding and collaborating with domain experts: It can be hard to find and collaborate with domain experts who have the time, w