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Systems Analysis and Design 8th EditionChapter 5Data and Process Modeling1Chapter Objectives Describe data and process modeling concepts and tools, including data flow diagrams, a data dictionary, and process descriptionsDescribe the symbols used in data flow diagrams and explain the rules for their useDraw data flow diagrams in a sequence, from general to specificExplain how to level and balance a set of data flow diagrams22Chapter ObjectivesDescribe how a data dictionary is used and what it containsUse process description tools, including structured English, decision tables, and decision treesDescribe the relationship between logical and physical models33IntroductionIn chapter 5, you use data and process modeling techniques to develop a logical model of the proposed system and document the system requirementsLogical model shows what the system must doPhysical model describes how the system will be constructed44Overview of Data and Process Modeling ToolsSystems analysts (SA) use many graphical techniques to describe an information systemA Data Flow Diagram (DFD) uses various symbols to show how the system transforms input data into useful information55Data Flow DiagramsA Data Flow Diagram (DFD) shows how data moves through an information system but does not show program logic or processing stepsA set of DFDs provides a logical model that shows what the system does, not how it does it

66Data Flow DiagramsDFD SymbolsDFDs use four basic symbols that represent processes, data flows, data stores, and entitiesGane and Sarson symbol setYourdon symbol set

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FIGURE 5-3 Data flow diagram symbols, symbol names, and examples of the Gane and Sarson and Yourdon symbol sets7Data Flow DiagramsDFD SymbolsProcess symbolReceives input data and produces output that has a different content, form, or bothMust have at least one input and at least one outputContain the business logic, also called business rules that transforms the dataProcess name identifies its function (verb)Process number does not signify precedenceExamples: print bill add customer apply paymentReferred to as a black box8does not show program logic or processing steps

8Data Flow DiagramsDFD SymbolsRules for ProcessesProcesses cannot consume or create dataMust have at least 1 input data flow (to avoid miracles)Must have at least 1 output data flow (to avoid black holes)Should have sufficient inputs to create outputs (to avoid gray holes)

99Data Flow Diagrams

DFD SymbolsData flow symbolRepresents one or more data itemsThe symbol for a data flow is a line with a single or double arrowhead10FIGURE 5-5 Examples of correct combinations of data flow and process symbols10Data Flow Diagrams11DFD SymbolsData flow symbolSpontaneous generationBlack holeGray hole

FIGURE 5-6 Examples of incorrect combinations of data flow and process symbols. APPLY INSURANCE PREMIUM has no input and is called a spontaneous generation process. CALCULATE GROSS PAY has no outputs and is called a black hole process. CALCULATE GRADE has an input that is obviously unable to produce the output. This process is called a gray hole1112Data Flow DiagramsDFD SymbolsRules for Data FlowsFrom external entity (source) to systemFrom system to external entity (sink)From internal symbol to internal symbol, but always either start or end at a process

12Data Flow DiagramsDFD SymbolsData store symbolRepresent data that the system stores The physical characteristics of a data store are unimportant because you are concerned only with a logical modelA DFD does not show the detailed contents of a data store the specific structure and data elements are defined in the data dictionary

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Is a flat rectangle that is open on the right side and closed on the left sideAt least has 1 incoming & outgoing data flow

13Data Flow DiagramsDFD SymbolsData store symbol

14FIGURE 5-7 Examples of correct uses of data store symbols in a data flow diagram

FIGURE 5-8 Examples of incorrect uses of data store symbols: Two data stores cannot be connected by a data flow without an intervening process, and each data store should have an outgoing and incoming data flow1415Data Flow DiagramsDFD SymbolsRules for Data StoresInternal to the systemData at restInclude in system if the system processes transform the dataStore, Add, Delete, UpdateEvery data store on DFD should correspond to an entity on an ERD

15Data Flow DiagramsDFD SymbolsEntity SymbolShows how the system interfaces with the outside worldA DFD shows only external entities that provide data to the system or receive output from the systemName of the entity appears inside the symbolEach entity must be connected to a process by a data flow

Terminators: because they are data origins or final destinations SourceEntity that supply data to the systemSink Entity that received data from the system

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16Data Flow DiagramsDFD SymbolsEntity Symbol

17FIGURE 5-9 Examples of correct uses of external entities in a data flow diagramFIGURE 5-10 Examples of incorrect uses of external entities. An external entity must be connected by a data flow to a process, and not directly to a data store or to another external entity

1718Data Flow DiagramsDFD SymbolsRules for EntityExternal people, systems and data storesReside outside the system, but interact with systemEithera) receive info from systemb) trigger system into motionc) provide new information to system1819YESNO

Keep in mind:All flow lines must be labeledLarge processes can be broken down into smaller componentsRules For Using DFD Symbols19Creating a Set of DFDsCreate a graphical model of the information system based on your fact-finding resultsThree-step processStep 1: Draw a context diagramStep 2: Draw a diagram 0 DFDStep 3: Draw the lower-level diagrams2020Creating a Set of DFDsGuidelines for Drawing DFDsDraw the context diagram so that it fits on one pageUse the name of the information system as the process name in the context diagramUse unique names within each set of symbolsDo not cross linesProvide a unique name and reference number for each processObtain as much user input and feedback as possible

2121Creating a Set of DFDsStep 1: Draw a Context Diagram22

22Creating a Set of DFDsStep 2: Draw a Diagram 0 DFD23

23Creating a Set of DFDsStep 2: Draw a Diagram 0 DFDIf same data flows in both directions, you can use a double-headed arrowDiagram 0 is an exploded view of process 0Parent diagramChild diagramFunctional primitive2424

Creating a Set of DFDsStep 3: Draw the Lower-Level DiagramsMust use leveling and balancing techniquesLeveling examplesUses a series of increasingly detailed DFDs to describe an information systemExploding, partitioning, or decomposing2525Creating a Set of DFDs

Step 3: Draw the Lower-Level DiagramsBalancingEnsures that the input and output data flows of the parent DFD are maintained on the child DFD

2626Data DictionaryA data dictionary, or data repository, is a central storehouse of information about the systems dataAn analyst uses the data dictionary to collect, document, and organize specific facts about the systemAlso defines and describes all data elements and meaningful combinations of data elements2727Data DictionaryA data element, also called a data item or field, is the smallest piece of data that has meaningData elements are combined into records, also called data structuresA record is a meaningful combination of related data elements that is included in a data flow or retained in a data store2828Data DictionaryUsing CASE Tools for DocumentationThe more complex the system, the more difficult it is to maintain full and accurate documentationModern CASE tools simplify the taskA CASE repository ensures data consistency2929Data DictionaryDocumenting the Data ElementsYou must document every data element in the data dictionaryThe objective is the same: to provide clear, comprehensive information about the data and processes that make up the system

3030Data DictionaryDocumenting the Data ElementsThe following attributes usually are recorded and describedData element name and labelAliasType and lengthDefault valueAcceptable values - Domain and validity rules3131Data DictionaryDocumenting the Data ElementsThe following attributes usually are recorded and describedSourceSecurityResponsible user(s)Description and comments3232Data Dictionary

Documenting the Data FlowsThe typical attributes are as followsData flow name or labelDescriptionAlternate name(s)OriginDestinationRecordVolume and frequency3333Data DictionaryDocumenting the Data StoresTypical characteristics of a data store areData store name or labelDescriptionAlternate name(s)AttributesVolume and frequency

3434Data Dictionary

Documenting the ProcessesTypical characteristics of a process Process name or labelDescriptionProcess numberProcess description

3535Data DictionaryDocumenting the EntitiesTypical characteristics of an entity includeEntity nameDescriptionAlternate name(s)Input data flowsOutput data flows

3636Data Dictionary

Documenting the RecordsTypical characteristics of a record includeRecord or data structure nameDefinition or descriptionAlternate name(s)Attributes

3737Data DictionaryData Dictionary ReportsMany valuable reportsAn alphabetized list of all data elements by nameA report describing each data element and indicating the user or department that is responsible for data entry, updating, or deletionA report of all data flows and data stores that use a particular data elementDetailed reports showing all characteristics of data elements, records, data flows, processes, or any other selected item stored in the data dictionary3838Process Description ToolsA process description documents the details of a functional primitive, which represents a specific set of processing steps and business logicIt should be noted that this chapter deals with structured analysis, but the process description tools also can be used in object-oriented development, which is described in Chapter 63939Process Description ToolsModular DesignBased on combinations of three logical structures, sometimes called control structures, which serve as building blocks for the processSequenceSelectionIteration - looping40

FIGURE 5-31 Selection structureFIGURE 5-30 Sequence structure40Process Description ToolsStructured EnglishMust conform to the following rulesUse only the three building blocks of sequence, selection, and iterationUse indentation for readabilityUse a limited vocabulary, including standard terms used in the data dictionary and specific words that describe the processing rules4141Process Description ToolsStructured EnglishMight look familiar to programming students because it resembles pseudocodeThe primary purpose of structured English is to describe the underlying business logic

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42Process Description ToolsDecision TablesShows a logical structure, with all possible combinations of conditions and resulting actionsIt is important to consider every possible outcome to ensure that you have overlooked nothing

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43Process Description ToolsDecision TablesThe number of rules doubles each time you add a conditionCan have more than two possible outcomesOften are the best way to describe a complex set of conditions4444Process Description ToolsDecision TreesGraphical representation of the conditions, actions, and rules found in a decision tableWhether to use a decision table or tree often is a matter of personal preference

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45Logical Versus Physical ModelsWhile structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information systemA physical model shows how the systems requirements are implemented4646Logical Versus Physical ModelsSequence of ModelsMany systems analysts create a physical model of the current system and then develop a logical model of the current system before tackling a logical model of the new systemPerforming that extra step allows them to understand the current system better4747Logical Versus Physical ModelsFour-Model ApproachDevelop a physical model of the current system, a logical model of the current system, a logical model of the new system, and a physical model of the new systemThe only disadvantage of the four-model approach is the added time and cost4848Chapter SummaryDuring data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful informationThe end product of data and process modeling is a logical model that will support business operations and meet user needsData and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions4949Chapter SummaryData flow diagrams (DFDs) graphically show the movement and transformation of data in the information systemDFDs use four symbolsA set of DFDs is like a pyramid with the context diagram at the top5050Chapter SummaryThe data dictionary is the central documentation tool for structured analysisEach functional primitive process is documented using structured English, decision tables, and decision treesStructured analysis tools can be used to develop a logical model during one systems analysis phase, and a physical model during the systems design phase

Chapter 5 complete

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