# Application Layer

### Application Service

* Defines the use case for the system
* Receives request from infra layer and coordinate the use of objects from domain layer and other layer

#### Note

* Application service operations can be represented by method (inside object) or function, using function is great if you're not planning to make the service stateful

### Data Transfer Object (DTO)

* Used to transfer data between application layer and infrastructure layer
* Should only contain data
* Should not contain behaviour
* Can be mutable or immutable, make it mutable only if it needs to be modified on transfer