by Vaughn Vernon
“Domain-Driven Design Distilled” (AKA DeDeDe-DeDe-DeDe…) is a sequel to the previous DDD book from Vaugh Vernon. It's a concise guide to understanding and implementing Domain-Driven Design (DDD) principles in software development. The book focuses on the core concepts of DDD, with practical examples to help developers apply these principles in real-world projects.
The most valuable points from the book are:
Ubiquitous Language
Ubiquitous Language is a shared vocabulary between domain experts and developers to facilitate clear communication and ensure a shared understanding of the domain. The book recommends this common language be used throughout the development process, from requirements gathering to implementation.
For example, when developing an e-commerce system, domain experts and developers should use the same terms, such as “Order,” “Product,” and “Customer,” to avoid confusion and miscommunication.
Bounded Context
Bounded Context is a concept that emphasizes the importance of defining clear boundaries around a particular domain or subdomain, ensuring that models and concepts within the context remain consistent and coherent.
For example, in a large organization with multiple departments, each department might have its own Bounded Context, ensuring that the models and concepts within each department are consistent and do not leak into other departments. This is "loose coupling and cohesion".
Entities, Value Objects, and Aggregates
DDD distinguishes between Entities, Value Objects, and Aggregates as the core building blocks of domain models. Entities have a unique identity and lifecycle, while Value Objects are immutable and represent a specific value. Aggregates are clusters of related domain objects that are treated as a single unit for consistency and transactional purposes.
For example, in a banking system, an Account can be an Entity, a MonetaryAmount can be a Value Object, and a BankTransaction can be an Aggregate that consists of multiple related objects, such as Debit and Credit.
Domain Events
Domain Events are occurrences within the domain that triggers a change in state or a business process. They are used to decouple components and promote a more modular, event-driven architecture. This is different than any other concept of "event", which may carry a different meaning, say a NodeJS event.
For example, in an e-commerce system, a ProductSold event can be triggered when a customer completes a purchase, allowing other components to react to this event, such as updating inventory or sending a confirmation email.
Repositories and Factories
Repositories and Factories are patterns used in DDD to manage the lifecycle of domain objects (usually Aggregates). Repositories are responsible for persisting and retrieving domain objects, while Factories handle the creation and initialization of domain objects.
For example, an OrderRepository can be responsible for saving and retrieving Order domain objects, while an OrderFactory can create new Order objects based on specific business rules.
Strategic Design and Context Mapping
Strategic Design and Context Mapping are techniques used in DDD to manage the complexity of large-scale systems and the relationships between different Bounded Contexts. Context Mapping helps identify dependencies, overlaps, and potential conflicts between different Bounded Contexts.
For example, when integrating multiple systems, Context Mapping can be used to identify areas of potential misalignment or integration challenges.
Related read: Event Storming.
By understanding and applying the core principles of Domain-Driven Design, developers can create more maintainable, scalable, and robust software systems that accurately model complex business domains and facilitate better communication between domain experts and developers.
Now you know when someone invokes DeDeDeDeDeDe… they're ok, and it's an actual thing; no need to call an ambulance.
Thanks for reading. If you have feedback, contact me on Twitter, LinkedIn or Github.
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