Ass.10 (SAD1)

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

In order to understand a Data FLow Diagram let's first define it:

Data Flow Diagram is a “description of data and the manual and machine processing performed on the data as it moves and changes from one stage to succeeding stages of the diagram. A typical DFD doesn’t show information on how the process will operates, the sequence of the processes.

Here are some characteristics of a Data Flow Diagram to ensure quality:

1. Design and Information Flow

• Data flow-oriented design, i.e., “structured design”, defines a number of different mappings that transform information flow into program structure.

2. Two Information Flow Types

• A transform flow is a segment of a DFD that consists of an incoming flow, a transform center, and an outgoing flow.

3. Design Process Considerations

• The transition from information flow to structure is accomplished as part of a five-step process:
(1) The type of information flow is established;
(2) flow boundaries are indicated;
(3) the DFD is mapped into program structure;
(4) the control hierarchy is defined;
(5) the resultant structure is refined using design measures and heuristics.

4. Completeness

• A quality Data Flow Diagram must check the completeness of the process model, particularly in the understanding of data which are being required by the system being modeled.
5. Simplifying Complexity

In making diagram especially if the system to be modeled is a complex one, it must be ensured that items in the diagram are being simplified. One characteristic that a quality Data Flow Diagram must have is simplifying complexity by isolating some major process.

6. Symbols

One important thing to consider in quality data flow diagram is the use of correct and understandable symbols. It should be considered that in making diagrams it must follow the correct usage of symbols in naming the flows of data whether inflows or outflows

Common symbols used in Data Flow Diagrams are the following:

1. Squares representing external entities, which are sources or destinations of data.
2. Rounded rectangles representing processes, which take data as input, do something to it, and output it.
3. Arrows representing the data flows, which can either be electronic data or physical items.
4. 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.

And most of all, an analyst must know if the developer of the process model follow the stages in making DFD’s.

The normal stages are:

1. Model the current system as it is presently implemented. It is rare that a system is designed to do something entirely new.

2. The essential activities of the system are extracted. What is now left is just the data, information stores and starts and destinations. What is removed is physical things like any IT used, the media on which the data is recorded and stored, and who does what

-The DFD remaining is called the Current Logical System.
-Make minor improvements in the logic of stored data
-Combine references to data stores using replicated data
-Remove data stores which are only used because of inefficiencies in the present system

3. Eventually the new system takes physical shape according to factors like the existing IT platform it will have to operate on, the data model adopted by the organization and organizational procedures favored within the corporate culture.




References:

http://faculty.babson.edu/dewire/Readings/dfddiag.htm
www.cems.uwe.ac.uk/~gwatkins/.../04.../lec2data_flow_diagrams.doc