I want you to consider a very simplified business system. You might think about an online ordering system, a billing system for a small consultant office or something else with very little processing. Something you know and understand might work better. Write a brief description of what has to be done in this system. Then draw a context diagram and a level 0 DFD. I am looking for something with about the same complexity as the Grading System illustrated in your text

I see this as an interactive process. You draw the diagrams and send them to me, I will comment and get back to you and we will try to work out a good set of diagrams between us. You tell me when it is done and ready to grade! I find that drawing diagrams in Word is reasonably easy - you can also try PowerPoint.