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-
- They show the passage of data through the system.
- They focus on the process that transform the incoming data flows(input) into outgoing data flows(output).
- External entities send and recieve data flows from the system.
- 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
- 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.
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.
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.
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.