What is a Data Flow Diagram?

Instructor: Lucinda Stanley

Lucinda has taught business and information technology and has a PhD in Education.

In this lesson, you'll learn what a data flow diagram is, how it is different from a flow chart, and some common uses for data flow diagrams. You'll also find out how to create your own simple data flow diagram.

Data Flow Diagrams and NASA

Did you know NASA uses data flow diagrams, such as this one for essential systems engineering?

NASA Data Flow Diagram
NASA Data Flow Diagram

It's true! So, what is a data flow diagram?

Data flow diagrams are visual representations of how data will move within an information system. That sounds daunting doesn't it? Basically a data flow diagram shows a picture of how data will move into a process, what will happen to it while it is there, how and where the data will emerge or its output, and where the changed data will be stored.

Data flow diagrams can be used in any industry that needs to perform a structured analysis, such as in computer systems design and business development. Data flow diagrams can be used to visualize current systems or improve them to fix problems and make them more efficient.

Many people confuse data flow diagrams with flow charts and pseudocode. Flow charts show steps in a process, like this flow chart for the writing process. Keep in mind that a flow chart does not identify the inputs, the functions, or storage.

Flow Chart: Writing Process

Pseudocode is the text version of a data flow diagram.


Simple and Complex Diagrams

Data flow diagrams can be as simple as this:

Data Flow Diagram: Simple
Data Flow Diagram: Simple

They can also be more detailed, like the one shown below:

Data Flow Diagram: Detailed
Data Flow Diagram: Appaservers

Data flow diagrams can be more complex, such as the NASA essential systems diagram used at the beginning of this lesson.

Reading a Data Flow Diagram

In order to read a data flow diagram, you might want to familiarize yourself with the typical shapes used to create them, as shown in this chart:

Data Flow Diagram: Commonly Used Shapes
Data Flow Diagram: Commonly Used Shapes

Creating a Data Flow Diagram

Let's see what all that means in terms of creating our own simple data flow diagram. For example, what if we want to show the flow of data for a simple process, such as operating a lemonade stand? We'll need to track four things: the source of the data, the movement of the data, how the data interacts, and where the data or output will be stored.

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