A proprietary software design method devised by Ed Yourdon. It was one of the first methods in the group known collectively as structured systems analysis. Yourdon has diagram notations for ERA diagrams, dataflow diagrams, structure charts (module calls), and state-transition diagrams. Also supported are review techniques such as structured walk through, and guidelines for analysis and design that include qualitative assessment of the good and bad characteristics of a design. The method is supported by tools and is used both for real-time and data-processing applications.