What is DDD?

Domain-Driven Design (DDD) is a way of building software that focuses on the real-world problems it’s trying to solve. It encourages developers to work closely with experts from the business side so the code mirrors the actual business concepts and rules.

Let's break it down

  • Domain: The specific area of knowledge or activity (e.g., banking, healthcare, e-commerce) that the software is meant to support.
  • Driven: The design and decisions are guided by the domain, not by technical concerns first.
  • Design: The process of planning how the software’s parts fit together, using models that represent the domain.
  • Model: A simplified, shared representation of the domain that both developers and business experts understand.
  • Ubiquitous Language: A common set of terms that everyone (developers, analysts, managers) uses consistently, reducing misunderstandings.
  • Bounded Context: A clear boundary around a part of the system where a particular model and language apply, preventing confusion across different areas.

Why does it matter?

When software reflects the real business language and rules, it’s easier to change, less prone to bugs, and aligns better with what the business actually needs. This leads to faster delivery of useful features and lower long-term maintenance costs.

Where is it used?

  • Banking systems: Modeling accounts, transactions, and compliance rules so that code matches financial regulations.
  • Healthcare platforms: Representing patients, appointments, and insurance claims in a way clinicians and administrators understand.
  • E-commerce sites: Managing products, orders, and pricing strategies with a model that mirrors the sales process.
  • Logistics and supply-chain software: Coordinating shipments, inventory, and routing using domain concepts familiar to operations teams.

Good things about it

  • Creates a shared understanding between technical and business teams.
  • Produces code that is easier to evolve as business rules change.
  • Helps keep large codebases organized by separating concerns into bounded contexts.
  • Encourages clear, expressive naming, reducing the “translation” gap.
  • Improves testability because the domain logic is isolated from infrastructure details.

Not-so-good things

  • Requires significant upfront collaboration and time to build the domain model.
  • Can be overkill for small or simple projects where the overhead isn’t justified.
  • Learning curve: teams need to adopt new practices like ubiquitous language and bounded contexts.
  • Misapplication (e.g., forcing DDD on every part of a system) can lead to unnecessary complexity.