A data Flow Diagram (also called DFD) maps out the flow of information for any process or system. It shows where data comes from, which activities process the data, and whether the output results are stored or used by another activity or external entity.

A data flow diagram illustrates the movement and transformation of data between externals (entities) and processes. The output from one external or process is the input to another. The data flow diagram also illustrates the temporary or permanent repositories (referred to as data stores or terminators). These store data within a system or an organization.

The data defined should be described in a data dictionary (see technique Data Dictionary

Why use a Data Flow Diagram?

  • Replaces a laborious description/Portrays a complex process in a simple diagram

  • Visually represents your system and its interactions. Also illustrates connections to other systems.

  • Gives an overview of the information’s movements (How it enters and leaves a system, how it is transformed)

  • Helps to explain the logic behind the data flow within a system.

  • Can be used as part of system documentation.

  • Pinpoints its weaknesses, scope, interfaces, and boundaries

  • Identifies its needs

  • Helps with potential modifications

  • Can be used to analyze an existing system or model a new one

  • Ensures fluid communication between a system analyst and individuals

  • Helps to identify duplicated data elements or misapplied data elements.

  • May be used as a discovery technique for processes and data or as a Technique for the verification of functional decompositions or data models.

DFD does not illustrate a sequence of activities

DFD does not show you who performs the work nor does it show you any alternative paths through the process.

During requirements analysis, you will create additional diagrams known as entity relationship diagrams (ERDs). These represent the user’s view of the solution and its capabilities in terms of entities, attributes, and relationships. You will often refine these models during the design phase of the project, particularly if you are defining capabilities of a software application. During design, as the ERDs are refined, the physical data model (that will become the basis for a relational database) is ultimately created.


  • Inventory

How to use a Data Flow Diagram

Data flow diagram example

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