A Beginner's Guide to Data Flow Diagrams

Ask any professional athlete or business executive how they became successful, and they’ll tell you they mastered a process. By figuring out which of their habits led to success, which didn’t, and learning from past successes and failures, they could improve their efficiency, effectiveness, and productivity at work.

But implementing a process into a business, department, or even a team is a completely different animal than honing your own personal process. With so many moving parts, how do you track each aspect of your process, and, more challenging yet important than that, how do you refine it?

For almost 50 years, data flow diagrams have been one of the most simple and effective tools for organizations to understand, perfect, and implement new processes or systems. They’re visual representations of your process or system, so they make it easy to understand and prune.

Before we dive into how data flow diagrams can help you refine any of your business’ systems or processes, though, let’s go over what it exactly is.

What is a data flow diagram (DFD)?

A data flow diagram, or a DFD, is a visual representation of any process or system’s flow of information. By mapping out your process or system’s flow of data, DFDs help you better understand your process or system, uncover its kinks, improve it, and can even help you implement a new process or system. DFDs can range from simple overviews to complex, granular displays of a process or system.

DFDs became popular in the 1970s and have been able to maintain their widespread use by being easy to understand. Visually displaying how a process or system works can hold people’s attention and explain complex concepts better than blocks of text can, so DFDs are able to help almost anyone grasp a system or process’ logic and functions.

There are two types of DFDs -- logical and physical. Logical diagrams display the theoretical process of moving information through a system, like where the data comes from, where it goes, how it changes, and where it ends up.

Physical diagrams shows you the practical process of moving information through a system, like how your system’s specific software, hardware, files, employees, and customers influences its flow of information.

You can either use logical or physical diagrams to describe the same flow of information or you can use them in conjunction to understand a process or system on a more granular level. But before you can use a DFD to understand your system or process’ flow of information, you need to know the standard notations or symbols used to describe it.

Data Flow Diagram Symbols

Data Flow Diagram symbols are standardized notations, like rectangles, circles, arrows, and short-text labels, that describe a system or process’ data flow direction, data inputs, data outputs, data storage points, and its various sub-processes.

Yourdon & Coad and Gene & Sarson are the two main methods of notation used in DFDs, and they both use shapes and labels to represent the four main elements of a DFD -- external entity, process, data store, and data flow.

Picture Credit: Lucidchart

1. External Entity

An external entity, which are also known as terminators, sources, sinks, or actors, are an outside system or process that sends or receives data to and from the diagrammed system. They’re either the sources or destinations of information, so they’re usually placed on the diagram’s edges.

2. Process

Process is a procedure that manipulates the data and its flow by taking incoming data, changing it, and producing an output with it. A process can do this by performing computations and using logic to sort the data or change its flow of direction. Processes usually start from the top left of the DFD and finish on the bottom right of the diagram.

3. Data Store

Data stores hold information for later use, like a file of documents that’s waiting to be processed. Data inputs flow through a process and then through a data store while data outputs flow out of a data store and then through a process.

4. Data flow

Data flow is the path the system’s information takes from external entities through processes and data stores. With arrows and succinct labels, the DFD can show you the direction of the data flow.

But before you start mapping out data flow diagrams, you need to follow four rules of thumb to create a valid DFD.

1. Each process should have at least one input and one output.

2. Each data store should have at least one data flow in and data flow out.

3. A system’s stored data must go through a process.

4. All processes in a DFD must link to another process or data store.

The Different Levels of DFDs and the Context level Data Flow Diagram

DFDs can range from simple overviews to complex, granular representations of a system or process with multiple levels, numbered from 0 to beyond. But the most common and intuitive DFDs are Level 0 DFDs, which are called context diagrams. They’re digestible, high-level overviews of the flow of information through a system or process, so almost anyone can understand it.

Level 1 DFDs are still broad overviews of a system or process, but they’re also more detailed -- they break down the system’s single process node into subprocesses. Level 2 DFDs dive even deeper into detail by breaking down each process into granular subprocesses. Any DFD that goes past level 2 is rare -- there would be too much detail, which defeats its original purpose of being easy to understand.

DFD Example

Professionals in various industries, like software engineering, IT, business, and product management & design, can use DFDs to better understand, refine, or implement a new system or process.

 And to help you develop a concrete understanding of what a DFD looks like and how it can simplify your organization's complex systems and processes, here’s an example of a context level data flow diagram of a DVD borrowing system, like Redbox.

In this DFD, the customer is the source of information, the DVD borrowing system is the process, data flow, and data store, and the shopkeeper is the destination of information.

Picture Credit: Lucidchart

Perfecting Your Process

Every great athlete, executive, business, or service are not only focused on following a stellar process, but they're also obsessed with perfecting it. That said, creating and honing an effective process is one of the most challenging tasks in the working world. But if you can evaluate your organization’s process with data flow diagrams, your company will have a firm grasp on how to master it.