What does a data flow diagram illustrate?

A data flow diagram (DFD) is primarily used to represent how data moves through a system, including where data is stored, processed, and the interactions between different components. It illustrates the flow of data and highlights how it is transformed as it moves through various processes within the system. This visualization assists in understanding the data's journey, its origins, and its destinations, as well as identifying any potential changes that occur as it is processed.

In a DFD, different symbols represent processes, data stores, and data flows, enabling analysts and stakeholders to comprehend how data is being utilized and manipulated. This clarity is essential for identifying bottlenecks, inefficiencies, or areas for improvement in data handling.

The other options focus on different aspects of system representation. The flow of actions relates more to process diagrams, the sequence of state changes implies a focus on state-based modeling (like state transition diagrams), and the structure of the system points to architectural diagrams that do not specifically emphasize data flow.