Architecting Modern Java EE Applications

Separation of concerns

The application's responsibilities should be clearly defined and differentiated from other applications.

In the same way as with code level, the concerns of several applications should be separated. The single responsibility principle holds true here as well.

The application's concerns include all business concerns, application boundaries, and owned data. As the business logic evolves and changes over time, these concerns should be revisited from time to time. This may result in applications that split up or get merged into single ones. The responsibilities and concerns that emerge from the context map should be reflected in the system's applications.

Data and data ownership is an important aspect of distributed applications. ...