Making separation architectures serve the user

The authors refine the software architecture concept of the separation of concerns, or what has been traditionally known as separation of presentation from application, as applied to software products where functionality is divided between modules that interact directly with the human user and those that do not. Historically, software developers have interpreted separation of concerns to mean the complete isolation of generic presentation service from task-specific functionality. Recently, however users have begun to demand new, quite different functionality, and development of appropriate supporting application programs requires a different user-centered interpretation of the separation of concerns principle. A three-year reanalysis of separation architectures is presented, and it is shown how the two interpretations lead to a new understanding of products that interact with human users. Two user tasks, each of which is representative of a number of software systems, are described. One illustrates how a task based on the historical view can be reinterpreted with the new understanding, the the other epitomizes a task that requires the more recent view