What is a Service?

In Domain-Driven Design (DDD), a Service is a pattern used to encapsulate domain logic that doesn’t naturally fit within an entity or value object. Essentially, services are used to perform operations or tasks that are related to the domain but are not inherently part of the state or behavior of a single entity.

Here are some key characteristics of services in DDD:

1. Domain Service: This type of service contains domain logic that is not naturally part of an entity or value object. For example, if you have a domain where complex business rules need to be applied, a domain service can encapsulate that logic. Domain services should be stateless, meaning they don’t maintain any internal state between calls.

2. Application Service: This type of service acts as an intermediary between the domain layer and the user interface or other external systems. It handles application-specific logic, such as coordinating tasks between different domain services or managing transactions.

3. Infrastructure Service: These are services that interact with external systems or infrastructure, such as databases, messaging systems, or third-party APIs. They are part of the infrastructure layer and support the domain logic by providing necessary integrations.

In summary, services in DDD help organize and manage domain logic that doesn’t naturally fit within entities or value objects, ensuring that the domain model remains clean and focused on its core responsibilities.