What is Data Flow Diagrams and how to write it

[Steyn]

I need some urgent information from you all. As related to my studies, i wanted to know what is Data Flow Diagrams (DFD) and Please suggest the good example how to write DFD ?

[JonathanD]

Data flow diagrams illustrate how data is processed by a system in terms of inputs and outputs.Dataflows are pipelines through which packets of information flow. Label the arrows with the name of the data that moves through it.They are used to describe how the system transforms information. They define how information is processed and stored and identify how the information flows through the processes.When building a data flow diagram, the following items should be considered:

• where does the data that passes through the system come from and where does it go,
• what happens to the data once it enters the system (i.e., the inputs) and before it leaves the system (i.e., the outputs),
• what delays occur between the inputs and outputs (i.e., identifying the need for data stores).

DFD is a graphical representation of the flow of data between processes.In other words, it shows:

1. What goes in
2. How it is changed
3. What comes out

[chroma]

Data Flow Diagram:
Draw data flow diagrams in several nested layers. A single process node on a high level diagram can be expanded to show a more detailed data flow diagram. Draw the context diagram first, followed by various layers of data flow diagrams.

Start from the context diagram. Identify the parent process and the external entities with their net inputs and outputs.Place the external entities on the diagram. Draw the boundary. Identify the data flows needed to generate the net inputs and outputs to the external entities.Identify the business processes to perform the work needed to generate the input and output data flows.Connect the data flows from the external entities to the processes.
Identify the data stores.

Connect the processes and data stores with data flows.Apply the Process Model Paradigm to verify that the diagram addresses the processing needs of all external entities.Apply the External Control Paradigm to further validate that the flows to the external entities are correct.Continue to decompose to the nth level DFD. Draw all DFDs at one level before moving to the next level of decomposing detail. You should decompose horizontally first to a sufficient nth level to ensure that the processes are partitioned correctly; then you can begin to decompose vertically.

A context diagram is a top level (also known as Level 0) data flow diagram. It only contains one process node (process 0) that generalizes the function of the entire system in relationship to external entities.

[Solomon]

As an alternative to functional decomposition, consider using a bottom-up approach when the details about the system are well known. You can easily nest data flow diagrams in SmartDraw. Draw the high-level diagrams first, then select the process you want to expand, go to the Tools menu, and select Insert Hyperlink. Link the selected process notation to another SmartDraw diagram or a web page.Once linked, a small plus sign will appear in the object, and clicking on it opens the linked file.