Q:

what are the Data Flow Diagrams DFD?

What are DF Diagrams , and how they help project managers in their job?

A:

As you can see, is a data flow diagram a diagram that shows the dataflow in an application.
At the highest level you have the context diagram that can be represented as:
          +-------------+
input --> | Application | --> output
          +-------------+

You can zoom into the function to show detailed dataflow:

          +-------+      +--------+     +----------+
code  --> | lexer | -->  | parser | --> | treetool | --> grapical representation
          +-------+      +--------+     +----------+
              |              ^                 ^
              |              |                 |
              |              V                 |
              |    ================            |
              +--> | symbol table | -----------+
                   ================

As you see, there are functions and data stores. Functions can change the data and datastores are used to store and retrieve the data.

