Appendix BProcess Modeling

MANAGEMENT INFORMATION SYSTEMS 8/ERaymond McLeod, Jr. and George SchellCopyright 2001 Prentice-Hall, Inc.B-*

Data Flow Diagrams (DFDs)Graphic representation of a system that uses a small number of symbol shapes to illustrate how data flows through interconnected processes Most natural way to document processesEmphasis on processes rather than dataB-*

DFD SymbolsDFDs consist of four symbols1) Environmental elements called terminatorsPersonOrganizationAnother system2) Processes which transform inputs to outputsLabeled with verb and objectAlso labeled with system or computer program name

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DFD Symbols [cont.]DFD symbols [cont.]Data flows which consist of logically related data elements that travel from one point or process to another. In other words, data in motion.StructuresDivergeConverge

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DFD Symbols [cont.]DFD symbols [cont.]Data stores which are data repositories. In other words, data at rest.B-*

CustomerMailSalesorders Enteredsales ordersEnteredsales orderdata

Sortedsales recordsSales commissionreportSalesmanagerSales orderform file1.Open mail2.Enter salesorder data3.Sortsales order s4.ComputesalescommissionsA Data Flow Diagram (Figure 0 Diagram) of a Sales Commission SystemB-*

When Drawing a Context Diagram1. Use only a single process symbol2. Label the process symbol to represent the entire system3. Do not number the single process symbol4. Include all terminators for the system5. Show all the data flows between the terminators and the systemB-*

Sales CommissionSystemCustomerSales ManagerSales commission reportMailA Context Diagram of a Sales Commission SystemB-*

Figure n DiagramsDocuments a single process of a DFD in a greater amount of detailn represents the number of the process on the next higher level that is being documentedThe term leveled DFDs describe the hierarchy of diagrams ranging from context to the lowest-level figure n diagram B-*

Figure 4 Diagram of a Sales Commission System34.1Computecommissionamounts4.2AccumulatetotalsSalesmanagerSortedsalesrecordsCommissionamountsSalescommissionreportB-*

How Many Levels to Use?Restrict a single DFD to no more than six to eight processesUse another tool to document the lowest level of detail but use no more than a single page. B-*

Data Flow Diagramming Guidelines1. Label each data flow with a unique name.2. Keep data flow names constant between levels.3. Show proper disposition of records deleted from a data store.4. When documenting a computer program, do not include reads/writes.5. Avoid read-only processes.6. Write-only processes are permissible when time serves as the trigger.B-*

Structured EnglishNarrative form of computer code documentationBased on PseudocodeAbbreviated, formalized pseudocode in a particular format that looks like computer codeB-*

Structured English Guidelines1) Use a verb when describing each processing strip.2) Supplement verb with one or more objects when necessary.3) Use only three constructs of programming.SequenceSelectionRepetitionB-*

Structured English Guidelines [cont.]4) Use only data names defined in the data dictionary.5) Use uppercase for all data names and computer syntax.6) Indent to show a hierarchical structure.

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Structured English Guidelines [cont.]7) When documentation is subdivided into modules, use the first line of each module for an identifying label and leave at least one blank line in-between.8) Restrict each module to a single entry and exit point.B-*

Structure English ExampleSTART

Initialize storage TOTAL.SALES, TOT.COM = 0

Process sales data DO WHILE (more records) PERFORM READ DATA PERFORM PROCESS DATA PERFORM PRINT DATA END DO

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SummaryProcess modeling is an important part of system designVarious techniques exist for process modelingDFDsStructured EnglishManager can use Structured English and DFDs to communicate system requirementsB-*

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