The process model is typically used in structured analysis and design methods. Also called a data flow diagram (DFD), it shows the flow of information through a system. Each process transforms inputs into outputs. The model generally starts with a context diagram showing the system as a single process connected to external entities outside of the system boundary. This process explodes to a lower level DFD that divides the system into smaller parts and balances the flow of information between parent and child diagrams. Many diagram levels may be needed to express a complex system. Primitive processes, those that don't explode to a child diagram, are usually described in a connected textual specification. Yourdon/DeMarco DFD A Yourdon/DeMarco style DFD is shown below. It includes both data and control flow as required in the Hatley/Pirbhai method typically used in real-time system analysis and design. Gane & Sarson DFD The Gane & Sarson style DFD shown below is typically used for information systems. Here we show the flow of information in a small software company. Return to Software Models