Domain Objects

Domain objects provide a common ground in which developers and users can meet and discuss the application. Domain objects represent concepts that are familiar to users and experts in a specific field of interest. We reason about a banking application using accounts, deposits, withdrawals, interest rates, and the like. In an airline booking application, we speak of reservations, airplanes, seats, destinations, schedules, and so on, as concepts that we will find in our software object model. Later, we develop the underlying structures and code and run scenarios for using the software. Given that users and experts are familiar with these domain concepts, they can discuss these aspects of the application easily. They feel comfortable manipulating these domain objects’ information directly, and they understand the procedures for requesting their services.

For the developers, these domain objects are only the starting point for constructing a model of the domain and for developing the internal representations of these and additional concepts that will exist in the software machinery. Although the original, “common” concepts might not prove valuable in the executable system, they should be traceable through the design because they clearly express the stakeholders’ understanding and issues surrounding the application.