GREENPRINT: A Graphic Representation of Structured Programs

improve the readability of programs over existing techniques, a new program representation termed GREENPRINT has been developed and is discussed in this paper. GREENPRINTs (the name taken from the phosphorfluorescence of certain display terminals and paralleling the term blueprints) are tree-structured diagrams together with source code statements that represent the control structure of programs. Discussed in this paper are the diagram-ming conventions, control flow methodology, presentation graphics, and practical experience with GREENPRINTs. Flowcharts are the oldest graphic representations of programs. The works of Goldstine and von Neumann contain many flow-charts.' Largely due to processor speed and storage space limitations , early programs were not structured; branching to common code was important and occurred frequently. Later, high-level languages appeared and programs automatically generating flow-charts from program text were developed.' At the same time, p r e gram structures improved. Nassi-Shneiderman Diagrams (NSDS) were proposed much later to represent structured program^.^ In this form, such program constructs as if-then-else and loop are represented as nested boxes. With a high level of nesting, these charts become wide, and their elements vary in size. HIP0 charts attempt to capture the data flow of program segments by focusing on the representation of input data, process, and output data for program block^.^ Combinations of NSDs and H I m s can be found in the l i t e r a t ~ r e , ~ ' ~ and in some instances NSDS have been a u t e matically generated.7 Further improvement can be achieved by direct input of charts using interactive graphics. The earliest general-purpose graphics system was Sketchpad.8 More specialized approaches include block diagrammingg and, more recently, the direct input of NSDS.",'~ In the latter case, program text is automatically generated from NSDS. A recent example of the use of graphics in software design is the TELL system," where NSDs are used for detailed program description. Copying is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract may be used without further permission in computer-based and other information-service systems. Permission to republish other excerpts should be obtained from the Editor.