How to Design Data Flow Diagrams

Follow the flow of processing logic with a Data Flow Diagram

The most important objective of any system design is to deliver the stated requirements of the user. Given this, ensuring that your design is adhering to the specifications, you will see three main elements represented by a Data Flow Diagram (DFD)--namely performance, control and changeability. Keep in mind also that your DFD will be eloquent, concise and logically consistent throughout its life cycle. Unlike the flow chart, there is no "Start" or "Stop" in the DFD. DFDs will graphically represent processing of the flow of data as it moves from sources through operations between input and output repositories. You'll find that in any given system regardless of complexity, you will see three basic operations: input, processing and output.

Instructions

Designing Data Flow Diagrams

1. Begin with the input of the system. For example, a publishing company that sells books has two distinct input/output functions, Customers and Publishers. You can use squares labeled "Buyer" and "Publisher" to represent these.

2. Create "Data Stores." These, put simply, are repositories that can be databases, files, spreadsheets or whatever you need to store any pertinent data. In the publishing company example, categories may include "Books," "Customers," "Pending Orders," "Publisher Orders" and "Publishers." Diagram each of these as a narrow, horizontal open-ended rectangle and label each category.

3. Create the "Process" diagram. This is simply an upright rectangle with rounded corners. You'll represent each process involved in the publishing company example here. Continuing the example of the publishing company, enter "Order Verification," " Shipment Verification," "Assemble Orders," "Match Shipments to Pending Orders," and "Assemble Requisition to Publisher."

4. Assemble the flow of data by constructing labeled arrows to connect the "Data Stores," "Processes" and input/output entities of the Data Flow Diagram. In our publishing company example, an arrow should flow from the "Customers" to "Order Verification" representing the processing of an order from a customer. Credit and order history will flow from the "Customers" data store to the order verification process. Once the order is validated, a flow will go to "Pending Orders." "Pending Orders" will flow orders to the "Assign Shipment to Pending Orders" process.

5. Show the flow of data between data flow entities as data only, without attempting to depict physical movement of actual material.

References

• University of Missouri, St. Louis: Comparison of Diagramming Methods
• Microsoft: Create a data flow diagram