A Beginner’s Guide to Data Flow Diagrams

A Beginner's Guide to Data Flow Diagrams

Ask any professional athlete or business executive how they got successful and they will tell you they mastered a process. By finding out which of their habits worked and which did not work, they improved their efficiency, effectiveness, and productivity at work.

However, implementing a process in a company, department, or even a team is a completely different animal than improving your personal process. With so many moving parts, how do you track and refine every aspect of your business process?

Data flow diagrams offer companies a simple and efficient way to understand, perfect and implement new processes or systems. They are visual representations of your process or system so that you can easily understand and crop them.

Before we dive into how data flow diagrams can help refine your company’s systems or processes, let’s first look at exactly what it is.

What is a data flow diagram (DFD)?

A data flow diagram (DFD) is a visual representation of the flow of information through a process or system. DFDs will help you better understand process or system operation in order to identify potential problems, improve efficiency, and develop better processes. They range from simple overviews to complex, detailed displays of a process or system.

Data flow diagram

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DFDs became popular in the 1970s and have maintained their widespread use by being easy to understand. The visual indication of how a process or system is working can grab people’s attention and explain complex concepts better than text blocks, so DFDs can help almost anyone understand the logic and functions of a system or process.

There are two types of DFDs – logical and physical. Logical diagrams show the theoretical process of moving information through a system, e.g. B. where the data comes from, where it is going, how it changes and where it ends.

Physical diagrams show you the practical process of moving information through a system; B. How the specific software, hardware, files, employees and customers of your system affect the flow of information.

You can use either logical or physical diagrams to describe the same flow of information, or you can use them together to understand a process or system on a more detailed level. However, before you can use a DFD to understand the flow of information in your system or process, you must understand the standard notation or symbols used to describe it.

Data flow diagram symbols

Data flow diagram symbols are standardized notations such as rectangles, circles, arrows and short text names that describe the data flow direction of a system or process, data input, data output, data storage points and its various sub-processes.

Four common notation methods are used in DFDs: Yourdon & De Marco, Gene & Sarson, SSADM, and Unified. They all use the same labels and similar shapes to represent the four main elements of a DFD – external entity, process, data store, and data flow.

Data flow diagram symbols

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External unit

An external entity, also known as terminators, sources, sinks, or actors, is an external system or process that sends or receives data to and from the diagram system. They are either the sources or destinations of information, so they are usually placed around the edges of the chart. External entity symbols are similar across models, with the exception of Unified, which uses a stick figure drawing instead of a rectangle, circle, or square.


Process is a procedure that manipulates the data and its flow by taking in incoming data, modifying it and producing an output with it. A process can do this by performing calculations and using logic to sort the data or change its directional flow. Processes usually start in the upper left of the DFD and end in the lower right of the diagram.

Data storage

Data stores contain information for later use, such as: B. a file with documents waiting to be processed. Data input flows through a process and then through a data store, while data output flows from a data store and then through a process.

Data flow

The flow of data is the path that system information from external entities takes through processes and data stores. The DFD can show you the direction of the data flow with arrows and concise labels.

Before you begin mapping data flow diagrams, there are four best practices that you must follow to create a valid DFD.

1. Every process should have at least one entrance and one exit.

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

3. The stored data of a system must go through a process.

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

Levels of data flow diagrams

DFDs can range from simple overviews to complex, detailed representations of a system or process with multiple levels, starting with level 0. The most common and intuitive DFDs are level 0 DFDs, also called context diagrams. They are digestible high-level summaries of the flow of information through a system or process so that almost anyone can understand them.

Level 0: context diagram

This DFD level focuses on higher-level system processes or functions and the data sources that flow to or from them. Level 0 diagrams provide a simple, straightforward overview of a process or system.

Stage 1: Process decomposition

Level 1 DFDs still provide a comprehensive overview of a system or process, but are also more detailed – they divide the individual process nodes of the system into sub-processes.

Level 2: Deeper dives

The next level of DFDs goes into even greater detail by breaking each level 1 process into granular sub-processes.

Level3: increase complexity

Level 3 and higher DFDs are uncommon. This is mainly due to the level of detail required, which defeats the original purpose of being easy to understand.

Examples of data flow diagrams

Professionals in various industries such as software engineering, IT, e-commerce, and product management and design can use DFDs to better understand, refine, or implement a new system or process.

But what does a data flow diagram look like in practice – and how does it help your company? Here are three examples of how to contextualize the DFD impact.

1. Level 0 DFD

Level 0 DFD

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This level 0 DFD provides a context map of a securities trading platform. The data flows in one direction from the customer service assistant and broker to the platform and in two directions from the customer to the platform and back again.

2. Level 1 DFD

Level 1 DFD

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This level 1 DFD divides the customer process in more detail and expands it to include account creation, cash withdrawals and any securities transactions.

3. Level 2 DFD

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This level 2 DFD breaks down the “place order” process in order to contextualize the steps required to place the order – either from a client or from a broker. It’s even a third-party exchange center where transaction details are forwarded after the order is placed.

How to create a data flow diagram

  1. Select a system or a process.
  2. Categorize related business activities.
  3. Draw a context DFD.
  4. Check your work.
  5. Create child diagrams.
  6. Expand Processes to Level 1 DFDs.
  7. Repeat this process as needed.

1. Select a system or a process.

First, choose a specific system or process that you want to analyze. While any system or process can be turned into a DFD, the larger the process, the more complicated and difficult to contextualize the context. Whenever possible, start with a small feature or process that you want to improve.

2. Categorize related business activities.

Then categorize all activities associated with that process into external entities, data flows, processes, and data stores.

Consider a restaurant food ordering system. Customers are external entities, the food ordering system is a process, and the interaction between customers and the system (which goes both ways) is the flow.

Also worth mentioning? The ordering system also serves as a data store. For an SSADA model, this means that it is drawn as a rectangle with rounded corners and two horizontal lines to represent its dual function.

3. Draw a context DFD.

Now is the time to draw. DFDs can be created by hand using free templates available online or through browser extensions.

Start with a simple Level 0 DFD: start with your process or system, then map all the basic connections and operations.

4. Review your work.

Before diving into more complex DFDs, double-check the work already done to make sure it is correct and complete. If you’ve missed (or added) a process, entity, or flow, your next level DFDs may not make sense and you may have to start over.

5. Create sub-charts.

For each process or system described in your Level 0 DFD, create a new child diagram with its own entities and flows. Finally, you can use these child diagrams to connect processes together.

6. Expand Processes to Level 1 DFDs.

You should use your child diagrams to map more detailed connections between each process. In the case of our restaurant example, this could mean digging deeper into the food ordering system and how it relates to suppliers, managers, customers and kitchen staff.

7. Repeat this process as necessary.

Any process – no matter how large or small – can be redefined as a level 0 context diagram and the cycle can start over. Repeat these steps as needed to create as many DFDs as needed or break the processes further to develop Level 2, 3, and so on DFDs.

Perfect your process

While there is no such thing as a “perfect” data flow diagram, continued practice can help streamline the process and provide important insights into what is working, what is not, and where improvements can be made by your company that will have the greatest impact.

Your best bet? Remember the rule: keep it simple. Start with the context, build connected processes and repeat them as necessary to map important connections, operations and entities in your company.

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