Data Flow Diagram-Structured Software & Analysis Design

Data Flow Diagram(DFD)

It provides a logical module of the system and show the flow of data and the flow of logic involved.

Data flow diagram have following characteristicks-

  1. They show the passage of data through the system.
  2. They focus on the process that transform the incoming data flows(input) into outgoing data flows(output).
  3. External entities send and recieve data flows from the system.
  4. Data flow diagram is also known as bubble chart.

Symbols used in data flow diagram

Data flow diagram consist of a series of a symbol joint together by a line. There maybe a single level DFD for entire system or it maybe exploded into various level.

The top level DFD is often called a context diagram.

Four symbols used in DFD are –

  • External entity(source or sink)
  • Data Flow
  • Process
  • Data Store

Context Level DFD

Context Level DFD

DFD Level 0 is also called a Context Diagram. It’s a basic overview of the whole system or process being analyzed or modeled. It’s designed to be an at-a-glance view, showing the system as a single high-level process, with its relationship to external entities. It should be easily understood by a wide audience, including stakeholders, business analysts, data analysts and developers. It contains a single process that place main role in the entire system. It determines the boundary of the system and it’s environment.

context  diagram

DFD Level 1 provides a more detailed breakout of pieces of the Context Level Diagram. You will highlight the main functions carried out by the system, as you break down the high-level process of the Context Diagram into its subprocesses. 

Level 1 diagram

DFD Level 2 then goes one step deeper into parts of Level 1. It may require more text to reach the necessary level of detail about the system’s functioning.

Level 2 diagram

Progression to Levels 3, 4 and beyond is possible, but going beyond Level 3 is uncommon. Doing so can create complexity that makes it difficult to communicate, compare or model effectively.

Using DFD layers, the cascading levels can be nested directly in the diagram, providing a cleaner look with easy access to the deeper dive.

By becoming sufficiently detailed in the DFD, developers and designers can use it to write pseudocode, which is a combination of English and the coding language.  Pseudocode facilitates the development of the actual code.