You can use Data Flow Diagrams (DFDs) to create system blueprints that you can communicate to clients and users. You create DFDs as an early step in the structured analysis approach to system analysis.

A data flow diagram shows where the data comes from, where it goes, where it is stored, and what happens to it during the process. You can use data flow diagrams to show the overall picture of a system and some of the detail.

You start modeling the NSV-4 using a type of context diagram: the NSV-4 Data Flow diagram. A context diagram is the topmost NSV-4 diagram in a structured analysis. You use a context diagram to set the task of a system in the enterprise that you are modeling. You place one system function (process) symbol on the diagram, model the external parts and data that the system interfaces with; then create a child decomposition diagram to show more detail about the system.