ISBN : 978-81-963532-2-3 (E-Book) The input portion of the DFD includes processes that transform input data from physical (e.g.character from terminal) to logical forms (e.g. internal tables, lists, etc.). Each input portion iscalledanafferent branch. The output portion of a DFD transforms output data from logical to physical form. Each outputportion is calledanefferent branch.The remaining portion of a DFD is calledthe centraltransform. In the next step of transform analysis, the structure chart is derived by drawing one functionalcomponentforthecentraltransform, and theafferent and efferentbranches. These are drawn below a root module, which would invoke these modules.Identifying thehighest level input and output transforms requires experience and skill. One possible approach isto trace the inputs until a bubble is found whose output cannot be deduced from its inputs alone.Processes which validate input or add information to them are not central transforms. Processeswhichsortinputorfilterdatafromitare.Thefirstlevelstructurechartisproducedbyrepresenti ngeachinputandoutputunitasboxesandeachcentraltransformasasinglebox.Inthethirdstepoftransfor manalysis,thestructurechartisrefinedbyaddingsub-functionsrequired by each of the high-level functional components. Many levels of functional componentsmay be added. This process of breaking functional components into subcomponents is calledfactoring.Factoringincludesaddingreadandwritemodules,errorhandlingmodules,initializationandterminationprocess,identifyingcustomermodules,etc.Thefactor ingprocessiscontinued until all bubblesin theDFDarerepresented in the structurechart. 50 Software Engineering Keerthana P, Manasa KN, Ganga D Bengal
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