One of the hardest things to do in software development is to determine how long and how much it will take to deliver a new software product. Should it be so hard? The answer is not straightforward.
DFD Diagram Notations
Now we'd like to briefly introduce to you a few diagram notations which you'll see in the tutorial below.
An external entity can represent a human, system or subsystem. It is where certain data comes from or goes to. It is external to the system we study, in terms of the business process. For this reason, people used to draw external entities on the edge of a diagram.