DATA FLOW DIAGRAM: ELEMENTS, TYPES, EXAMPLES - TECHNOLOGY - 2024

The data flow diagram is a visual way to show the movement of data through an information system. It presents how information enters and leaves the system, what route it passes through, where it is stored, and the sources and destinations of that information.

Companies could not operate without systems and processes, and effectiveness is essential to achieve objectives. There are numerous ways to study this effectiveness, but the data flow diagram outperforms the others.

Example of a data flow diagram in Spanish

A data flow diagram or DFD shows how processes flow in a system. It is a graphical representation to show a system and, in turn, can help solve where there are problems and inefficiencies.

In a DFD the duration of the processes is not shown or if these processes operate in series or in parallel. There are no loops or loops, as there are in a network diagram, there are no decision points, as there are in a flow diagram.

Flowcharts are used to design, analyze, document or manage a program or process, being widely used in very different fields such as programming, cognitive psychology or economics and financial markets.

This results in the range of flowcharts being wide and dividing by types and classifications is needed.

Elements of a data flow diagram

The signs used in the data flow diagram describe the path of data in a system, storage sites, data inputs and outputs, and various threads. They are standardized notations like circles, rectangles, and arrows.

Various notation methodologies are used in DFDs. These have some differences, but they all use signs and shapes to represent the main elements of a DFD.

External entity

It can represent a human being, a system or a subsystem. It is the origin or destination of certain data. That is, it sends or receives data to or from the diagrammed system.

Depending on the business process, it is external to the system that is being analyzed. For this reason, external entities are commonly drawn to the edges of the DFD.

Process

It is an activity or business function where data and its flow are transformed, by changing, ordering or changing the direction of the flow. It takes the incoming data, changes it and with it produces an output.

A process can do this by performing calculations and also using logic to be able to sort the data or change the direction of the flow. It can be broken down to a higher level of detail to represent how data is processed within the process.

The processes are located between the input and the output, generally starting from the upper left of the DFD and ending in the lower right of the diagram. There can be several of them in a single diagram.

Data warehouse

It contains the information for later use, such as a document file that is waiting to be processed.

Data inputs can flow through a process and then into a data warehouse, while data outputs flow out of a data warehouse and then through a process.

Data flow

Represents the flow of information. It determines the itinerary that the information takes from external entities through the various processes and data warehouses. With arrows the DFD can show the direction of the data flow.

Rules for a DFD

Before you begin plotting data flow diagrams, there are four general rules of thumb to follow to create a valid DFD.

- Each data store must have at least one data input and output data stream.

- Each process must have at least one input and one output.

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

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

Types

Depending on what you want to examine in the flow, there are two types of data flow diagrams to choose from.

Logical

This type of diagram reflects what is happening in an information flow. It shows the information that is being generated and that which is being communicated, the entities receiving that information, the processes that are carried out in general, etc.

The processes described in a logic diagram are activities carried out in a company, which means that the technical aspects of the system are not studied in depth. Therefore, the staff is able to understand these diagrams without being technical.

Physical

This type of diagram reflects how information moves through a system. This represents that the programs, as well as the computer equipment, people and files involved in the information flow are specifically detailed.

The physical diagrams include the processes corresponding to data entry, such as the control check. Intermediate data storage, such as temporary tables or files, is also placed.

For example, you could show how a customer places an order online by reviewing the company's software to place and complete that order. This is generally technical.

Thus, a detailed physical diagram can greatly help to program the code required for the implementation of an information system.

Which one to use?

Both physical and logical diagrams can represent the same flow of information. However, each will have a different point of view and provide different activities to optimize the system.

They can be used together or separately. Together they provide more detail than either diagram alone. When deciding which to use, keep in mind that you might need both.

Examples

In software engineering, the data flow diagram can be designed to represent the system at different levels of abstraction.

Higher-level DFDs are divided into lower levels, thus addressing more information and functional elements. The levels in DFD are numbered 0, 1, 2 or more.

Level 0

It is outlined to reflect a perspective in which the entire system is encapsulated in a single process, indicating the relationship it has with external entities.

The input and output data are marked by arrows going into or out of the system. This level is called a context diagram.

Source: geeksforgeeks.org (CC BY-SA 4.0)

Level 1

At this level the context diagram is broken down into multiple processes. The main functions of the system are highlighted and the high-level process is broken down into sub-processes.

Source: geeksforgeeks.org-CC-BY-SA-4.0

Level 2

This level goes a little deeper than level 1. It can be used to record specific details about the operation of the system.

Source: geeksforgeeks.org (CC-BY-SA-4.0)

References

1. Computer Hope (2017). Data flow diagram. Taken from: computerhope.com.
2. W3 Computing (2019). Developing Physical Data Flow Diagrams. Taken from: w3computing.com.
3. Georgina Guthrie (2019). How to use data flow diagrams to supercharge your Project. Cacoo. Taken from: cacoo.com.
4. Geeks for Geeks (2019). Levels in Data Flow Diagrams (DFD). Taken from: geeksforgeeks.org.
5. Clifford Chi (2019). A Beginner's Guide to Data Flow Diagrams. Hub Spot. Taken from: blog.hubspot.com.