Now we have seen the concepts and implementations necessary to realize domain logic in our application. In theory it's already sufficient to implement standalone business logic; however, the use cases won't provide much value to the customer if they can't be accessed from outside of the system.

Therefore, let's have a look at technically motivated external and cross-cutting concerns. These are functionalities that are not at the core of the business domain, but that need to be fulfilled as well. Examples for technically motivated concerns are accessing external systems or databases, configuring the application, or caching.