Chapter 7 – Yourdon dataflow diagrams: A tool for disciplined requirements analysis

Publisher Summary This chapter describes the Yourdon Structured Method (YSM) for disciplined requirements analysis. The first obvious change from the early approach is the emphasis in YSM on modeling the behavior of a required system. The second change is the introduction of new graphical notations which are associated with particular aspects of modeling. The third change is the clearer distinction between modeling phases: YSM is divided into three distinct phases. The first is the feasibility study, which includes the study of any current system, and its environment. The second is essential modeling and the aim of this phase is to describe the essence of a software system in terms of how the required system must behave, and what data it must store. Essential modeling was derived from Essential Systems Analysis which provides many of the solutions to the problems with the old version of the Yourdon method. Its major contribution in this area is the clarification of the question of technology dependence which leads to a new way of constructing dataflow diagrams.