Process

How to read it

Ed Yourdon, in Just Enough Structured Analysis, defines the process as the part of a system that transforms inputs into outputs, and lists bubble, function and transformation as other names for it. Its label is usually a verb and an object, such as VALIDATE INPUT or COMPUTE TAX RATE, and most analysts number each bubble for reference. The UK Health Security Agency’s guidance on data flow diagrams sets out the two notations: circles for processes in Yourdon (1989) and DeMarco (1978), rounded rectangles in Gane and Sarson (1979).

Also searched as: data flow diagram process, dfd bubble, dfd circle, dfd process, process symbol.

Differences by notation

Yourdon calls the choice of shape purely cosmetic, as long as one shape is used throughout a diagram. He links the circle to the Yourdon/DeMarco camp, since YOURDON Press published its textbooks, and calls the Gane and Sarson shape an oval, introduced in their 1977 book; the UKHSA guidance and the University of Notre Dame’s business analysis guide describe it as a rounded rectangle. In his account a plain rectangle for a process comes from a third method, SofTech’s Structured Analysis Design Technique (SADT).

Look-alikes

In Yourdon/DeMarco notation a plain rectangle is an external entity, not a process. A flowchart step is a square-cornered process box, and a BPMN task is a rounded rectangle much like the Gane and Sarson process. A circle in a flowchart is a connector.