Flow Charting and Block Diagramming Techniques - All about the ...

Flow Charting and Block Diagra mmin g TechniquesIntroductionThe old cliche which so strongly points up the quantitativerelationship between words and pictures hasparticular truth in the development and documentationof data processing methods and procedures. Thesystems analyst finds use for many types of pictorialrepresentations, including forms layouts, control paneldiagrams, manpower loading charts, etc. The two tobe discussed here are the work-flow chart and the blockdiagram.A work-flow chart (or simply flow chart) is definedas a graphic representation of the system in whichdata provided by a source document is converted tofinal documents. (It should be noted here that in itsbroadest meaning a document is "any instrumentconveying information," Such a definition is used inthis discussion in order to include punched cards,magnetic tape and paper tape in the same categoryas printed forms.) A flow chart, then, provides apicture of the data processing application from thestandpoint of what is to be accomplished. Such apicture gives primary emphasis to the documents involvedand secondary emphasis to the work stationsthrough which they pass.A block diagram is defined as a graphic representationof the procedures by which data is processedwithin a system. In this picture the emphasis is onthe operations and decisions necessary to complete theprocess.To put it another way, a flow chart serves to showwhat job is to be done, while a block diagram showshow a job is done. This interpretation is derived fromthe fact that flow charts are frequently composedsolely of symbols representing the form in which dataappears at various stages in a process. The actual operationswhich must be performed are indicated onlybriefly or not at all.In order to encourage standardization in the useof symbols, thereby simplifying the problem of interchanginginformation between IBM and its customers,IBM has made available the Charting and DiagrammingTemplate shown in Figure 1. The cutoutscan be used to draw symbols representing clericalfunctions, unit record machines and functions, dataprocessing systems and functions, and various typesof documents.In the pages that follow, the standard symbols usedin flow charts and block diagrams will be described.When preparing charts and diagrams for publicationor presentation, it is common practice to introducemore artistic variations of the symbols. One frequentvariation is the use of photographic reductions representingthe actual forms and machines used in aprocedure.Flow ChartingDirection of FlowThe basic element of the flow chart (and the blockdiagram as well) is the line and arrow (Figure 2)indicating DIRECTION OF FLOW (y, z)*. In order for onesymbol to have a meaningful relationship to othersymbols in a chart it is necessary that it be connectedto one or more other symbols in such a way as toindicate the sequence in which the operations occuror the disposition of the documents.*Letters in parentheses following the name of a symbol refer tothe location of the symbol on the template as illustrated inFigure 1.A11Figure 2. Direction of FlowIn flow charting, solid lines are normally used, butoccasionally it is desirable to differentiate between thephysical movement of work and the mere transfer ofinformation. This can be done by using solid linesin the first case and dotted lines in the second. Forexample, dotted lines are used to illustrate accountingcontrol functions.Flow charts are constructed to conform to the naturaltendency to read from left to right, top to bottom,5