Data Flow Diagram

Data Flow Diagrams (DFDs) show the input and output of a system, and how data is processed. DFDs focus on how information moves through a system – what data goes into it, what data comes out, and where it gets stored.

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A DFD is a type of flowchart that can be used to generate an overview of the data flows among different dimensions of an application, system or project. Manual or automated, Data Flow Diagrams can be combined to best depict the requirements of your system.

The DFD maps out the entire system to show where a system starts, how the information is decomposed, and how it flows through the system. This documentation can help communicate the boundaries of a system to other parts of an organization as well as provide a starting point for redesigning a system.

History of Data Flow Diagrams

Data flow diagrams became popular in the 1970s. They are used to visualize software systems before UML diagrams and were originally described in Larry Constantine and Ed Yourdon’s 1971 Structured Design text.




Data flow diagrams originated in 1979. A popular technique for structured analysis and design, data flow diagrams use rounded rectangles to denote processes. Edward Yourdon and Tom DeMarco introduced another model in the 1980s that uses circles instead of rounded rectangles to denote processes.

DFDs are Essential features:

  1. Every title must be different. This enables referring to features in the DFD much lot simpler.
  2. It is important to remember that DFD is not a flowchart. Arrows are a flow chart that depicts the sequence of events; in DFD, arrows indicate flowing data. There is no chronological order to a DFD.
  3. Stop yourself from making reasonable decisions. If the impulse to draw a diamond-shaped box in a DFD ever arises, we must resist it! In flow charts, a diamond-shaped box is used to indicate decision points with numerous possible paths, only one of which is chosen. This suggests an event sequence, which is illogical in a DFD.
  4. Don’t get too caught up in the details. Error conditions and error handling should be left till the end of the analysis.

Data Flow Diagrams Symbols

In data flow diagrams, there will be fundamentally two types of abbreviations that define separate visual representations for functions, data structures, information flows, and external data.

Data flow diagrams of the Yourdon and Coad types are commonly used for analysis and design, whereas Gane and Sarson DFDs are more commonly used for visualising information systems.

The most prominent visual difference between the two methods of designing data flow diagrams is the appearance of activities. Activities are represented as circular in the Yourdon and Coad diagram, whereas they are squares with rounded corners in the Gane and Sarson diagram.

Process Notations.

The Process Receiving data flow is transformed into exiting data flow by a process.

Datastore Notations.

Datastores are the system’s data repository. They’re also known as files on occasion.

Dataflow Notations.

Dataflow Notations are a type of dataflow diagram. Dataflows are informational channels that carry packets of data. The names of the data that moves via the arrows should be labelled.

External Entity Notations.

External entities are elements that interact with both the system from outside the systems. The system’s inputs and outputs come from and go to external entities.


A method that changes data inputs into data outputs is indicated by a circle.

Data Flow:

The movement of data into or out of a procedure or data repository is depicted by a curving line.

Data Store:

A group of parallel lines denotes a location where data items can be collected. A data store denotes the storage of information which can be retrieved at a later time or by other procedures in a different format. A single element or a set of elements can be found in the data storage.

Source or Sink:

An external entity that operates as a resource of system inputs or a source of system outputs is known as a source or sink.

Data Flow Diagram Levels

At any level of complexity, the DFD can be designed to perform a system software. In reality, DFDs can be divided into levels, each of which represents a higher level of information flows and operational depth. In DFD, levels are numbered 0, 1, 2, or higher.

0-level DFDM

The core system model, also known as a context diagram, depicts the complete software requirements as a single bubble with incoming and outgoing arrows denoting input and output data. After that, the system is divided into a DFD with many bubbles. Each of these bubbles represents a different part of the system, which is then dissected and documented as more thorough DFDs. This approach can be done as many times as needed until the system is completely comprehended. The number of inputs and outputs must be preserved between levels, which DeMacro refers to as levelling.

1-level DFD

A case diagram is divided into numerous bubbles/processes in 1-level DFD. At this tier, we identify the system’s major goals and split down the high-level 0-level DFD procedure into subcomponents.

2-Level DFD

2-level DFD explores even further into the sections of 1-level DFD. It could be used to project or record specific/necessary information about how a system works.


Q1. What is DFD in software engineering with example?

A data-flow diagram is a visual representation of data flowing through a device or a process. The DFD also includes information on every entity’s inputs and output, as well as the operation overall.

Q2. What are the uses of data flow diagram?

Data flow diagrams show consumers how data in a software application goes through one operation to another. Information technology professionals and systems analysts use data flow diagrams to describe and demonstrate users how data is transferred across different operations in a system.

Q3. What are the main components of DFD?

In data flow diagrams consist four primarycomponents i.e. entity, process, data store and data flow. External Entity – External entities, also called as actors, providers or sinks, and terminators, generate and consumes data passing between both the entity as well as the diagrammed system.

Q4. How many types of DFD?

The data flow diagram must generally consist of three levels: 0-level DFD, 1-level DFD, and 2-level DFD. DFD at 0 levels: A context diagram is another name for it. It’s meant to be a simplification perspective, with the system depicted as either a single operation with external systems.

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