If we were to organize the module contents, our first attempt probably would be to design the inner package structure by technical layering. Slicing up by business concerns first and technical ones second at least sounds reasonable.

In the users package this would mean to have sub-packages such as controller, business or core, model, data and client, respectively. By following this approach, we split up responsibilities inside the users package by their technical categories. In order to be consistent, all the other modules and packages in the project would have similar packages, depending on their contents. The idea is similar to a three-tier architecture, but inside of the domain modules.

One of the sub-packages would be considered to be the technical entry point, for instance controller. This package would contain the communication endpoints initiating the use case logic and serve as entry point outside of the application. The following shows the structure of a horizontally organized users package:

This structure is realized in Java packages as follows: