How do you use domain-driven design to learn and apply new knowledge?

1 Step 1: Define the domain

The domain is the area of interest or expertise that your software serves. It can be a specific business, industry, market, or problem. To define the domain, you need to identify the main goals, stakeholders, and challenges of your software project. You can use interviews, surveys, observations, or other methods to gather information from the domain experts, who are the people who know the domain best. You can also use existing documentation, such as requirements, specifications, or user stories, to understand the domain.

2 Step 2: Create the domain model

The domain model is a conceptual representation of the domain, using terms and concepts that are meaningful and relevant to the domain experts. The domain model can include entities, attributes, relationships, rules, and behaviors that describe the domain. You can use diagrams, such as class diagrams, entity-relationship diagrams, or state diagrams, to visualize the domain model. You can also use natural language, such as plain text, pseudocode, or domain-specific languages, to express the domain model.

3 Step 3: Define the bounded contexts

The bounded context is a subdomain that has a clear boundary and a consistent meaning. A bounded context can be a module, a service, a subsystem, or a component that encapsulates a set of domain concepts and rules. By defining bounded contexts, you can divide the domain into smaller and more manageable parts, and avoid ambiguity and inconsistency. You can use context maps, which are diagrams that show the relationships and dependencies between bounded contexts, to identify and communicate the boundaries.

4 Step 4: Design the aggregates

The aggregate is a cluster of domain objects that are treated as a unit for data changes and transactions. An aggregate has a root, which is the entity that controls the access and consistency of the aggregate, and boundaries, which are the rules that define what belongs to the aggregate and what does not. By designing aggregates, you can ensure the integrity and coherence of your data, and reduce the complexity and coupling of your code. You can use aggregate design patterns, such as factory, repository, or specification, to implement aggregates.

5 Step 5: Implement the domain services

The domain service is a class or a function that performs a domain operation that does not belong to any entity or value object. A domain service can encapsulate complex logic, coordinate multiple aggregates, or interact with external systems or services. By implementing domain services, you can separate the domain logic from the application logic, and make your code more modular and testable. You can use service design principles, such as single responsibility, loose coupling, or high cohesion, to design domain services.

6 Step 6: Refine the domain model

The domain model is not a static artifact, but a dynamic and evolving one. As you learn more about the domain, you may need to refine the domain model to reflect the new knowledge, feedback, or changes. You can use refactoring techniques, such as renaming, extracting, or simplifying, to improve the readability and maintainability of your code. You can also use domain events, which are messages that capture the occurrence of something important in the domain, to communicate and react to changes.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?