Context and Level 1 Data Flow Diagram Examples With Explanation and Tutorial

The best way to explain things is with examples. We will show you context (also called simple or level 0) and level 1 data flow diagram examples to understand better the meaning behind it.

On this page:

  • What is data flow diagram? Definition, advantages, and disadvantages – a tutorial for beginner.
  • Rules and symbols for creating DFD.
  • Context data flow diagram example (in PDF) with an explanation step by step.
  • Level 1 data flow model diagram example (in PDF) with an explanation.
  • How to draw DFD online? Best software tools and solutions.

Let’s define and explain it:

A data flow diagram (DFD) represents graphically a flow of data within a system. It illustrates how data is input and output from the system.

It also shows destinations, storage, and sources of the information in the system.




In other words, DFD represents the information flow as well as where data comes from, where data goes and how it is stored.

So, we can say a data flow diagram has 4 major elements:

  • Processes – the main activities that are happening within the system boundary. The process can be as simple as collecting customer data and storing it in the company database. Also, it can be a very complicated process such as creating a report containing bank contracts with customers of all bank clones in a region.
  • External entities – the sources of information coming to or leaving the system. External entities are outside systems such as people (customers, stakeholders, managers), organizations, computers and other systems that send or receive data from our system.
  • Data stores – places where data is held such as files or repositories. Data stores show information that is not moving.
  • Data flows – illustrate the movements that data have between the external entities, data stores, and the processes.

Symbols used in data flow diagrams

Each of the above elements has a symbol that represents it. Typically, data flow diagram uses the following symbols:

Symbols Used in Data Flow Diagrams

The above ones are so-called symbols of Yourdon and Coad.

There is also the symbol system of Gane and Sarson, but in our data flow diagram examples, we will use Yourdon and Coad symbols as they are easier for drawing and remembering.

DFD rules, guidelines, and tips:

Creating data flow diagrams requires some guidelines and rules that should be followed. These guidelines make DFD easily understandable and lucid.

Here are some of the key rules and tips.

1. Each process has at least one outgoing data flow and at least one ingoing data flow.

data flow diagram process example

2. Each process can go to any other symbol (other processes, data store, and entities).

data flow diagram process example

3. Each data store should have at least one incoming and at least one outgoing data flow.

data flow data store example

4. Entities must be connected to a process by a data flow.

data flow external entity example

5. Data flows cannot cross with each other.

6. Data stores cannot be connected to external entities. Otherwise, it means you’re allowing an external entity access to your data files and stores.

7. The labels of processes can be verb phrases. Data stores are displayed by nouns.

8. Data flows cannot run between two external entities without going through a process (as you will see in the data flow diagram examples below).

Advantages and disadvantages of data flow diagrams:

Before going further to data flow diagram examples, let’s see what are some key benefits and cons of DFD.

Advantages:

  • A graphical technique that is relatively easy to understand for stakeholders and other users.
  • Provides a detailed view of the system components and boundaries.
  • Provide clear and detailed information about the processes within a system.
  • Shows the logic of the data flow.
  • Presents a functional breakdown of the system.
  • Used as a part of the system documentation.

Disadvantages:

  • Takes a long time to create.
  • Does not give any information about the timing, sequence, and synchronization of processes i.e. data flow diagrams do not specify when the processes are performed. Therefore it should not be confused with a process or flowchart diagram which can illustrate these things.
  • Sometimes might be difficult for non-technical users to understand the diagram.

Data Flow Diagram Examples

1. Context data flow diagram: definition and example with explanation

When it comes to simple data flow diagram examples, context one has the top place.

Context data flow diagram (also called Level 0 diagram) uses only one process to represent the functions of the entire system.




It does not go into details as marking all the processes.

The purpose is to express the system scope at a high level as well as to prevent users from deep down into complex details.

The major advantage of context DFD is simplicity.

Key context DFD characteristics:

  • Simple to draw.
  • No need of technical knowledge to understand it.
  • Shows the system boundaries.

Steps for creating a context DFD:

  • Step1: Define the process.
  • Step2: Create a list of all external entities (all people and systems).
  • Step3: Create a list of the data flows.
  • Step4: Draw the diagram.

Let’s illustrate the things with a context data flow diagram example.

Below is shown a simple context DFD drawn for a Clothes Ordering System and explanation.

context data flow diagram example

Download the above diagram in PDF

Now, let’s explain how we create the diagram.

Srep1: Define the process.

As it is a context data flow diagram, the process is only one. In our case, it is Clothes Ordering System. Draw a rectangle for the process.

Step 2: Create the list of all external entities.

In our example, the external entities are: Customer, Clothes Store, Clothes Supplier, and the Sales Manager. These are all entities who are involved with our system. Also, now you can draw a rectangle for each of the entities.

Step 3: Create a list of the data flows.

In between our process and the external entities, there are data flows that show a brief description of the type of information exchanged between the entities and the system.

In our example, the list of data flows includes: Customer Order, Receipt, Clothes Order, Receipt, Clothes Order, and Management Report.

Now, connect the rectangles with arrows signifying the data flows.

If data flows both ways between any two rectangles, create two individual arrows.

Step4: It is our diagram.

2. Level 1 data flow diagram: definition and example with explanation

As you saw above context DFD contains only one process and does not illustrate any data store.

This is the main difference with level 1 DFD.

Level 1 DFD breaks down the main process into subprocesses that can then be seen on a more deep level. Also, level 1 DFD contains data stores that are used by the main process.

Steps for creating a context DFD:

  • Step1: Define the processes (the main process and the subprocesses).
  • Step2: Create a list of all external entities (all people and systems).
  • Step3: Create a list of the data stores.
  • Step4: Create a list of the data flows.
  • Step5: Draw the diagram.

Here is our level 1 data flow example – a decomposition of the Clothes Ordering System illustrated in the context DFD.

level 1 data flow diagram example

Download the above diagram in PDF

As you see, the above Clothes Order System Data Flow Diagram Example shows three processes, four external entities, and also two data stores.

Here are the steps for creating the level 1 DFD:

Step 1: Define the processes.

The three processes are: Order Clothes, Generate Reports, and Order Inventory.

Step 2:  Create the list of all external entities.

The external entities are: Customer, Clothes Store, Sales Manager, and Supplier

Step 3: Create the list of the data stores.

These are: Order and Inventory

Step 4: Create the list of the data flows

Data flows are: Order, Bill, Order, Order, Inventory details, Inventory details, Orders, Reports, Inventory Order, Inventory Order, Inventory details.

Step5: Create the diagram.

How to Create Data Flow Diagrams?

It might seem a little bit difficult to create data flow diagram examples. But in our IT world, it can be very easy and even fun to make them using the appropriate software tools.

You can use paid or free graphing software, free mind mapping software or diagramming solutions such as:

The diagramming software tools like the above ones provide pre-ready templates that save your time and efforts.

They also make creating multi-level DFD (such as level 2 DFD) easier and at the same time deeper enough to represent clearly how the data is handled.

These tools also allow building very visually appealing DFDs with the use of a variety of shapes, colors, symbols, and arrows.

Conclusion

In addition to the context and level 1 data flow diagram, there are also level 2 and level 3 DFD.

Level 2+ DFD just breaks processes down into more subprocesses. Teoritucaly, DFD could go even beyond level 3, but they rarely do this on practice.

Hopefully, the above tutorial and context and level data flow diagram examples help you understand better the meaning and steps for creating DFDs.

Data flow diagrams are very useful types of graphs in the business that can support your data-driven decision-making, simply because the businesses are based on systems and processes.

From customer ordering methods to banking processes and operations, nearly everything an organization makes involves a system and processes of some sort.

That’s why the data flow diagram is a valuable way in which business can express and communicate important information.



One Response

  1. Violet July 26, 2019

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