Mastering DDD: How Domain‑Driven Design Reshapes Your Project Architecture

Traditional Development Layers

Traditional data‑driven development follows a three‑tier View‑Service‑DAO structure, producing procedural code where objects are merely data carriers (anemic model). Design is driven by database ER diagrams, and the layers mainly handle data processing and implementation.

What is DDD?

Domain‑Driven Design (DDD) is an object‑oriented modeling methodology for tackling complex software systems. It bridges analysis and design by introducing a unified domain model, reducing the gap between requirements and implementation.

DDD emphasizes placing the domain model at the core, enabling software to adapt quickly to changing requirements.

DDD Terminology and Core Concepts

Domain: the bounded context that defines the problem space.

Sub‑domain: a further division of a domain to manage high complexity.

Core domain, generic sub‑domain, and supporting sub‑domain categorize sub‑domains by importance.

Ubiquitous language: a shared vocabulary that eliminates communication barriers among developers, product managers, QA, etc.

Bounded context: defines the limits of a model’s applicability.

Aggregate: a cluster of related entities and value objects treated as a single unit, governed by an aggregate root.

Aggregates must contain required information; otherwise they are invalid.

Internal objects must satisfy business rules.

Only one aggregate root exists, which other entities depend on.

External access is limited to the aggregate root, which maintains internal consistency.

Aggregate root: the single entry point of an aggregate.

Entity: an object with a unique identifier.

Value object: an object without a unique identifier.

Common Domain Models

Anemic model

The domain object contains only persistence‑independent logic, while persistence‑related logic resides in the Service layer, leading to a heavy Service.

Domain logic tightly coupled to persistence is split to Service.

Service layer becomes overly thick.

2. Rich (or "charged") model

Business logic is placed primarily in the Domain, with a thin Service layer handling only transaction concerns, avoiding direct DAO interaction.

DDD Layered Architecture

Our team adopts the following DDD‑based layers:

Interaction layer: Web, Task, and other projects at the top.

Application layer: Service API and Service Provider projects; API projects expose DTOs and service interfaces without depending on other projects.

Domain layer: pure domain model project, containing only OO implementations without data access.

Infrastructure layer: split into Component and Repository projects; Components provide shared utilities, Repositories handle domain storage. The Domain layer does not depend on Repository; instead, Repository depends on Domain via dependency injection.

The whole system is tightly integrated with Spring, using factories to create prototype aggregate roots, entities, and value objects, and injecting repository implementations dynamically.

Benefits of DDD

All participants work around a unified domain model, eliminating the split between analysis and design.

DDD places domain and design at the core, fostering collaboration between developers and business stakeholders, improving delivery quality and reducing maintenance cost.

The layered architecture separates business complexity from technical complexity, keeping the domain model and code aligned.

Ubiquitous language ensures clear, unambiguous concepts across contexts, while bounded contexts control model complexity.

DDD’s tactical patterns (aggregate, entity, value object, service, factory, repository) classify model elements and define their responsibilities, lowering the cost of building domain models.