After the responsibilities of the system landscape have been defined, the boundaries of dependent systems need to be specified.
In previous chapters, we have seen various communication protocols and how to implement them. Besides the actual implementation, the question is now: how to design the interfaces of applications? Which aspects need to be considered, especially in distributed systems?
The applications within a system are carved out based on their business responsibilities.
Similarly, the application's API should represent that business logic as well. The exposed API represents the business use cases a certain application comprises. This implies that a business domain expert can, without any further technical knowledge, identify the exposed business use cases from an API.
The business use cases are ideally offered in clear, lean interfaces. Invoking a use case should not require more technically-motivated communication steps or details...