The DoDAF models in the Systems Viewpoint describe systems and interconnections providing for, or supporting, DoD functions. DoD functions include warfighting and business functions.
In the Systems diagrams, you associate systems resources to the operational and capability requirements. The systems resources support the operational activities and facilitate the exchange of information. The Systems models support legacy systems. As architectures are updated, you can transition from Systems to Services and utilize the models in the Services Viewpoint.