 The method was regularly taught and distributed among Capgemini consultants and customers, until the waterfall method slowly went out of fashion in the wake of more iterative extreme programming methods such as Rapid application development, Rational Unified Process and Agile software development.In the early to mid-1970s, the various generic work steps of system development methodologies were replaced with work steps based on various structured analysis or structured design techniques.SDM, SDM2, SDM/70, and Spectrum evolved into system development methodologies that were based on the works of Steven Ward, Tom Demarco, Larry Constantine, Ken Orr, Ed Yourdon, Michael A. Jackson and others, as well as data modeling techniques developed by Thomas Bachmann and Peter Chen.