What is Domain Modeling in DDD?
Domain modeling is at the heart of Domain-Driven Design (DDD) — it’s how we translate complex business domains into structured, meaningful code. In DDD, we focus not just on data, but on behavior and rules that mirror the real world.
Here’s a clear, actionable step-by-step breakdown for applying domain modeling in DDD.
Visit my previous article, for the run down on what DDD is: https://buildfactory.dk/what-is-domain-driven-design-ddd-and-how-do-i-use-it/
✅ Step-by-Step: Domain Modeling in Domain-Driven Design
1. Define the Bounded Context
Start by identifying clear boundaries in your system — where the language, logic, and rules stay consistent. This helps avoid confusion and overlapping logic.
2. Collaborate with Domain Experts
Work closely with non-technical stakeholders to capture domain language and key concepts. This shared vocabulary becomes your ubiquitous language.
3. Identify Aggregates
Group related objects into Aggregates, each managed by an Aggregate Root. Think of it as the authoritative gateway for its related objects.
Example: An
Orderaggregate may includeOrderItems, but all changes go through theOrder.
4. Model Entities and Value Objects
- Entities have identity (e.g.,
Customer,Invoice) - Value Objects are defined only by their attributes (e.g.,
Address,Money) and are immutable.
5. Define Domain Services
Some logic doesn’t belong to any specific entity or value object. That’s where domain services come in — they model behaviors as standalone operations.
6. Capture Invariants and Business Rules
- Invariants are rules that must always be true within an aggregate.
- Business Rules are broader rules that may span across multiple aggregates or contexts.
🔎 Quick Tip: Invariants are local and strict; business rules can be global and flexible.
7. Design Repositories
Define Repository Interfaces to abstract how aggregates are saved and loaded. Keep infrastructure concerns (like database logic) out of the domain model.
8. Iterate and Refine the Model
Use techniques like Event Storming, feedback loops with stakeholders, and ubiquitous language to continuously evolve your domain model.
🔄 Why Iteration Matters
The domain model is never “done.” As business needs shift, your model should adapt. That’s the beauty of DDD — it’s designed for evolution.
🧠 Final Thoughts
Domain modeling in DDD helps developers and businesses speak the same language. By aligning your code with real-world behavior, you create software that’s more flexible, maintainable, and meaningful.
Whether you’re building microservices or refining a legacy monolith, start with the domain — and let the model grow with your understanding.
📌 Summary Table
| Concept | Description |
|---|---|
| Bounded Context | Defines consistent terminology and logic boundaries |
| Entity | Object with identity |
| Value Object | Object defined only by its data |
| Aggregate | Cluster of entities/VOs with a root |
| Domain Service | Stateless behavior outside entities |
| Invariant | Rule that must always be true within an aggregate |
| Business Rule | General rule that reflects domain logic |