Key Terms in Domain-Driven Design

Have you heard of Domain-Driven Design (DDD), a major software design approach?

DDD was introduced in Eric Evans’ classic book “Domain-Driven Design: Tackling Complexity in the Heart of Software”. It explained a methodology to model a complex business. In this book, there is a lot of content, so I’ll summarize the basics.

The composition of domain objects:

• Entity: a domain object that has ID and life cycle.

• Value Object: a domain object without ID. It is used to describe the property of Entity.

• Aggregate: a collection of Entities that are bounded together by Aggregate Root (which is also an entity). It is the unit of storage.

The life cycle of domain objects:

• Repository: storing and loading the Aggregate.

• Factory: handling the creation of the Aggregate.

Behavior of domain objects:

• Domain Service: orchestrate multiple Aggregate.

• Domain Event: a description of what has happened to the Aggregate. The publication is made public so others can consume and reconstruct it.