Yourdon dataflow diagrams: A tool for disciplined requirements analysis

During the past two decades many informal methods for requirements analysis and specification have been proposed. The majority of these claim to be ‘structured’ and have a graphical notation as a central component. The simplicity of some of these notations has made them popular with analysts and acceptable to their customers. However, vagueness in early descriptions of the syntax and semantics of the notations has allowed an unhelpful degree of flexibility in their application and interpretation, and has diminished their usefulness. Dataflow diagrams, as promoted by the Yourdon organization, have suffered in this way. This tutorial introduces the notation and describes how it has been used and how it should be used.