 Bubbles are usually grouped into higher level bubbles to decrease complexity.Data dictionaries are needed to describe the data and command flows, and a process specification is needed to capture the transaction/transformation information.SA and SD are displayed with structure charts, data flow diagrams and data model diagrams, of which there were many variations, including those developed by Tom DeMarco, Ken Orr, Larry Constantine, Vaughn Frick, Ed Yourdon, Steven Ward, Peter Chen, and others.