Common Data Flow Diagram Symbols
Terminals: These oblong shapes are used to mark the start and end points of a process.
Process Boxes: These rectangular boxes are used to denote a process or action. A process can be identified as an activity that adds to, transforms or changes the input into something different. For instance – compiling data into a report or extracting some information from the data are processes and must be presented in rectangular boxes, on the flow diagram.
Alternate Process: Sometimes more than one process option is available to complete a certain task, these alternate process options are shown in rectangles with rounded corners.
Decision Points: Any point on the data flow diagram where a decision needs to be made is represented as a rhombus or a diamond. These decision points usually address yes and no types of questions. Thus there are normally two different data courses out of the decision box – one for the course to be adopted if the condition is true and the second if the condition is false. Besides the usual yes and no conditions, there may be other conditions which may have more than two answers, like if the data flow requires examining a variable Y in relation to a variable X there may be three possibilities – X=Y, X>Y and X<Y. This would, mean three different processes flowing out of the decision box.
Flow Connectors: Circles are used to mark connectors, which denote a jump point in the flow chart from one point to another. The connectors are used for breaking long flow lines that continue elsewhere on the flow diagram. Assigning each connector a reference number makes it easier for the end user to understand from where to where a jump is needed.
Directional Arrows: These are used to demonstrate the directional flow of the data and guide the user to the next step on the flow diagram.
Off Page Connector: An off page connector symbol is used to show where a part of the data flow diagram continues on another page. The reference page number is mentioned in the connector.
Data Boxes: These are used to display the input and output data related to a process.
OR Logical Operator: Wherever the user needs to choose one or more options from the available options an OR logical operator symbol is used on the flow arrows depicting the various options.
AND Logical Operator: Any point on the data flow where the two or more options must be used simultaneously, the AND logical operator symbol is displayed on the arrows leading to the options.
Merge Triangle: Wherever information from two or more sources needs to be merged together, it is represented on the data flow diagram using a triangle.
Extract: If some information needs to be extracted from the database it is shown using an inverted triangle.
Document: The symbol used for showing any document that will be created or used in the data flow chart is shown using a torn piece of paper.
These are some of the standard data flow diagrams symbols, and while there are no penalties for deviating from these standards, using different symbols can lead to confusion among the end users.