Assignment 10 (SAD 1)

With reference to assignments 8 and 9, what characteristics does an analyst (you) examine when evalauating DFD quality? (1500 words)

Before going through the characteristics that an analyst must have in order to properly evaluate a DFD, let us first define what Data Flow Diagram is and how to create it. After showing the basics of a DFD, I will enumerate and briefly explain the characteristic as based on the previous assignments.

What is a DFD?
A data-flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. DFDs can also be used for the visualization of data processing (structured design). A DFD provides no information about the timing of processes, or about whether processes will operate in sequence or in parallel. It is therefore quite different from a flowchart, which shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored (all of which are shown on a DFD).

The data flow diagram has a purpose and it provide a semantic semantic bridge between users and systems developers. And it diagrams are first graphical, eliminating thousands of words; second is logical representations, modeling WHAT a system does, rather than physical models showing HOW it does it; third is hierarchical, showing systems at any level of detail; and last jargonless, allowing user understanding and reviewing

One of the characteristic for the evaluation of the DFD quality: Completeness. DFDs offer a way to check the completeness of the process model, particularly with regards to the understanding of the data that would be required by an information system (e.g., is all the data that would be needed for input actually available? Does each processing step produce data that could be used by subsequent steps? Is all data generated usable by an information system where necessary?). DFDs can provide a fast way to generate further questions that need to be asked about the process.
All diagrams must have a basic DFD symbol present for the system.
Here are examples of symbol of a DFD using Gane and Sarson notation.
*Squares representing external entities, which are sources or destinations of data.
*Rounded rectangles representing processes, which take data as input, do something to it, and output it.
*Arrows representing the data flows, which can either, be electronic data or physical items.
*Open-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.

Data flow Diagram symbols:


Reference:
http://www.agilemodeling.com/artifacts/dataFlowDiagram.htm