States & Transitions

Define How the Domain Changes

Things in a business are rarely static.

An order can be created, confirmed, fulfilled and cancelled.

A claim can be submitted, reviewed, approved or rejected.

A contract can be drafted, signed, active or terminated.

The state of an entity is part of the domain.

States Describe Reality

A state represents a meaningful condition within the domain.

It tells the system what is currently true.

But a state alone is not enough.

The domain also needs to define how change occurs.

Transitions Define Change

Transitions describe how an entity moves from one state to another.

They can depend on:

Rules.

Conditions.

Permissions.

Events.

Operations.

Other entities.

This creates a formal representation of how the business evolves over time.

Behavior Becomes Explicit

Without explicit states and transitions, business behavior often becomes scattered across code paths.

With them, the lifecycle of an entity becomes part of the specification itself.

That makes behavior easier to understand, validate and generate.

The Domain as a Living System

A domain is not simply a collection of objects.

It is a system of things that continuously change.

States and transitions provide the language for describing that change.

Model how the domain changes, and its behavior becomes part of its definition.