Data Flow Diagrams as described in "Structured Analysis and System Specification" (Tom DeMarco) are lightweight and provides a common way to describe a system w

Data Flow Diagrams as described in "Structured Analysis and System Specification" (Tom DeMarco) are lightweight and provides a common way to describe a system with a focus on the flow of data. The book also goes into detail on how to apply it. e.g., the value of having simple diagrams and have separate diagrams to break down the more complex processes in detail. It's not rocket science, but I have found it helpful in the past to communicate ideas or existing designs.