Final answer:
A physical data flow diagram (DFD) uses bubbles to represent processes in a system and shows the flow of data between these processes.
Step-by-step explanation:
Physical Data Flow Diagram
A physical data flow diagram (DFD) is a graphical representation of a system that shows the flow of data between various processes and the entities that interact with the system. Bubbles, also known as circles or nodes, are used in a physical DFD to represent processes.
These bubbles specify where, how, and by whom a system's processes are accomplished. For example, if you have a system for online shopping, one bubble might represent the process of adding items to a shopping cart, another bubble might represent the process of entering payment information, and so on.
Here is an example of a physical data flow diagram for an online shopping system:
In this diagram, each bubble represents a specific process in the online shopping system, and the arrows represent the flow of data between these processes.