Using Data Flow Diagrams
Key Points and Objectives
Data flow diagrams (DFDs) are one of the main methods available for analyzing data-oriented systems.
Through the use of (DFDs), which emphasize the logic underlying the system, the systems analysts can put together a graphical representation of data movement through the organization.
The data flow approach has four main advantages over the narrative explanation of the data movement. They are:
Freedom from committing to the technical implementation of the system too early B.
Further understanding of the interrelationships of systems and subsystems C. C.
Communicating current system knowledge to users through data flow diagrams D.
Analysis of the proposed system to determine if all the data and processes have been defined.
Four basic symbols are used to chart data movement on data flow diagrams. They are:
A double square for an external entity--a source or destination of data
An arrow for movement of data from one point to another
A rectangle with rounded corners for the occurrence of transforming process
An open-ended rectangle for a data store.
Correct naming of data flow objects is necessary for good communication. Guidelines are:
External entities should be named with a noun.
Processes should be named:
A system name
A subsystem name
With a verb-adjective-noun format.
Processes should have a unique reference number.
Data stores should be named with a noun.
Use the following guidelines to develop a data flow diagram:
Make a list of business activities.
Create the context level diagram, including all external entities and the major data flow to or from them.
Create Diagram 0 by analyzing the major activities within the context process. Include the external entities and major data stores.
Create a child diagram for each complex process on Diagram 0. Include local data stores and detailed processes.
Detailed data flow diagrams may be developed by:
Analyzing what happens to an input data flow from an external entity.
Analyzing what is necessary to create an output data flow to an external entity.
Examining the data flow to or from a data store.
Analyze a well-defined process for data requirements and the nature of the information produced.
Unclear areas of a data flow diagram should be noted and investigated.
An interface data flow is data that is input or output from a child diagram that matches the parent diagram data flow.
Processes that do not create a child diagram are called primitive processes. Logic is written for these processes.
The following conditions are errors that occur when drawing a data flow diagram:
If a process only input data flow or only output data flow from it.
When data stores or external entities are connected directly to each other, in any combination. C.
Incorrectly labeling data flow or objects. Examples are:
Labels omitted from data flow or objects.
Data flow labeled with a verb.
Processes labeled with a noun.
Too many processes on a data flow diagram. Nine is the suggested maximum.
Omitting data flow from the diagram.
Unbalanced decomposition between a parent process and a child diagram. The data flow in and out of a parent process must be present on the child diagram.
Logical data flow diagrams show how the business operates and include processes that would exist regardless of the type of system implemented.
The progression of creating data flow diagrams is:
Create a logical data flow diagram of the current system.
Next, add all the data and processes not currently in the system which must be present in...
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