The Application Model describes the application software needed to support the business functions. The three diagrams in the Application Model provide a useful way to capture your system as it is.
Note It is ideal, particularly for larger projects, to model both the "as is" and the "to be" systems. There are some smaller projects, however, which begin with modeling the "to be" system.
The three diagrams in the Application Model are (from the most general to the most detailed perspective):
System Context Diagram
A high level Data Flow diagram showing an application with its interfaces to computer systems. It should only show the scope and interfaces of a single release of the application.
System Area Map
Provides a high-level graphical view of your Enterprise's present applications. Compared to other diagrams, the System Area Map has a relatively loose, simple format. Each System Area map should have an Architecture diagram to go with it.
System Architecture Diagram
Gives a high level description of the characteristics of the Applications that satisfy the business requirements. System Architect implements the System Architecture diagram using a Data Flow Diagram format, similar to the System Context diagram.