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Chapter Objectives Describe data and process modeling conceptsand tools, including data flow diagrams, a datadictionary, and process descriptions Describe the symbols used in data flow diagramsand explain the rules for their use Draw data flow diagrams in a sequence, fromgeneral to specific Explain how to level and balance a set of dataflow diagrams1

Chapter Objectives Describe how a data dictionary is used andwhat it contains Use process description tools, includingstructured English, decision tables, anddecision trees Describe the relationship between logical andphysical models2

Introduction In Chapters 5 & 6, you will develop a logicalmodel of the proposed system and documentthe system requirements– Logical model shows what the system mustdo– Physical model describes how the systemwill be constructed3

Overview of Data and ProcessModeling Tools Systems analysts use many graphicaltechniques to describe an information system A data flow diagrams (DFD) uses varioussymbols to show how the system transformsinput data into useful information4

Data Flow Diagrams A data flow diagram (DFD) shows how datamoves through an information system butdoes not show program logic or processingsteps A set of DFDs provides a logical model thatshows what the system does, not how it doesitFigure 5-25

Data Flow Diagrams DFD Symbols– DFDs use four basic symbols that representprocesses, data flows, data stores, andentities Gane and Sarson symbol set Yourdon symbol set– Symbols are referenced by using all capitalletters for the symbol nameFor more information aboutYourdon Symbols visitscsite.com/sad8e/more,locate Chapter 5 and thenthe Yourdon Symbols link.Figure 5-36

Data Flow Diagrams DFD Symbols– Process symbol Receives input data and produces output that hasa different content, form, or both Contain the business logic, also called businessrules Referred to as a black boxFigure 5-47

Data Flow Diagrams DFD Symbols– Data flow symbol Represents one or more data items The symbol for a data flow is a line with a singleor double arrowhead Spontaneous generation Black hole Gray holeFigure 5-5Figure 5-68

Data Flow Diagrams DFD Symbols– Data store symbol Represent data that the system stores The physical characteristics of a data store areunimportant because you are concerned onlywith a logical model Is a flat rectangle that is open on the right sideand closed on the left sideFigure 5-7Figure 5-89

Data Flow Diagrams DFD Symbols– Entity Symbol Is a rectangle, which may be shaded to make itlook three-dimensional Name of the entity appears inside the symbol Terminators Source SinkFigure 5-9Figure 5-10Figure 5-1110

Creating a Set of DFDs Create a graphical model of the informationsystem based on your fact-finding results Three-step process– Step 1: Draw a context diagram– Step 2: Draw a diagram 0 DFD– Step 3: Draw the lower-level diagrams11

Creating a Set of DFDs Guidelines for Drawing DFDs– Draw the context diagram so that it fits onone page– Use the name of the information system asthe process name in the context diagram– Use unique names within each set of symbols12

Creating a Set of DFDs Guidelines for Drawing DFDs– Do not cross lines– Provide a unique name and reference numberfor each process– Obtain as much user input and feedback aspossible13

Creating a Set of DFDs Step 1: Draw a Context Diagram– Context diagram– Start by placing a single process symbol inthe center of the page– Process 0– Identify the entities and the name andcontent of the data flows, and the directionof the data flowsFigure 5-12Figure 5-1314

Creating a Set of DFDs Step 2: Draw a Diagram 0 DFD– Diagram 0– Must retain all the connections that flow intoand out of process 0– Each process has a reference number– Diverging data flowFigure 5-14Figure 5-1515

Creating a Set of DFDs Step 2: Draw a Diagram 0 DFD– If same data flows in both directions, youcan use a double-headed arrow– Diagram 0 is an exploded view of process 0– Parent diagram– Child diagram– Functional primitiveFigure 5-1616

Creating a Set of DFDs Step 3: Draw the Lower-Level Diagrams– Must use leveling and balancing techniques– Leveling examples Uses a series of increasingly detailed DFDs todescribe an information system Exploding, partitioning, or decomposingFigure 5-17Figure 5-1817

Creating a Set of DFDs Step 3: Draw the Lower-Level Diagrams– Balancing Ensures that the input and output data flows ofthe parent DFD are maintained on the child DFDFigure 5-19Figure 5-20Figure 5-21Figure 5-2218

Data Dictionary A data dictionary, or data repository, is acentral storehouse of information about thesystem’s data An analyst uses the data dictionary to collect,document, and organize specific facts about thesystem Also defines and describes all data elementsand meaningful combinations of data elementsFor more information aboutData Dictionaries visitscsite.com/sad8e/more,locate Chapter 5 and thenthe Data Dictionaries link.19

Data Dictionary A data element, also called a data item orfield, is the smallest piece of data that hasmeaning Data elements are combined into records,also called data structures A record is a meaningful combination ofrelated data elements that is included in adata flow or retained in a data store20

Data Dictionary Using CASE Tools for Documentation– The more complex the system, the moredifficult it is to maintain full and accuratedocumentation– Modern CASE tools simplify the task– A CASE repository ensures data consistency– You will learn more about CASE tools inPart 2 of the Systems Analyst’s Toolkit21

Data Dictionary Documenting the Data Elements– You must document every data element inthe data dictionary– The objective is the same: to provide clear,comprehensive information about the dataand processes that make up the systemFigure 5-23Figure 5-2422

Data Dictionary Documenting the Data Elements– The following attributes usually are recordedand described Data element name and labelAliasType and lengthDefault valueAcceptable values - Domain and validity rules23

Data Dictionary Documenting the Data Elements– The following attributes usually are recordedand described SourceSecurityResponsible user(s)Description and comments24

Data Dictionary Documenting the Data Flows– The typical attributes are as follows Data flow name or labelDescriptionAlternate name(s)OriginDestinationRecordVolume and frequencyFigure 5-2525

Data Dictionary Documenting the Data Stores– Typical characteristics of a data store are Data store name or labelDescriptionAlternate name(s)AttributesVolume and frequencyFigure 5-2626

Data Dictionary Documenting the Processes– Typical characteristics of a process Process name or labelDescriptionProcess numberProcess descriptionFigure 5-2727

Data Dictionary Documenting the Entities– Typical characteristics of an entity include Entity nameDescriptionAlternate name(s)Input data flowsOutput data flowsFigure 5-2828

Data Dictionary Documenting the Records– Typical characteristics of a record include Record or data structure nameDefinition or descriptionAlternate name(s)AttributesFigure 5-2929

Data Dictionary Data Dictionary Reports– Many valuable reports An alphabetized list of all data elements by name A report describing each data element and indicatingthe user or department that is responsible for dataentry, updating, or deletion A report of all data flows and data stores that use aparticular data element Detailed reports showing all characteristics of dataelements, records, data flows, processes, or anyother selected item stored in the data dictionary30

Process Description Tools A process description documents the detailsof a functional primitive, which represents aspecific set of processing steps and businesslogic It should be noted that this chapter dealswith structured analysis, but the processdescription tools also can be used in objectoriented development, which is described inChapter 631

Process Description Tools Modular Design– Based on combinations of three logicalstructures, sometimes called controlstructures which serve as building blocksfor the process1. Sequence2. Selection3. Iteration - loopingFigure 5-30Figure 5-31Figure 5-3232

Process Description Tools Structured English– Must conform to the following rules Use only the three building blocks of sequence,selection, and iteration Use indentation for readability Use a limited vocabulary, including standardterms used in the data dictionary and specificwords that describe the processing rulesFor more information aboutStructured English visitscsite.com/sad8e/more,locate Chapter 5 and thenthe Structured English link.33

Process Description Tools Structured English– Might look familiar to programming studentsbecause it resembles pseudocode– The primary purpose of structured English isto describe the underlying business logicFigure 5-33Figure 5-3434

Process Description Tools Decision Tables– Shows a logical structure, with all possiblecombinations of conditions and resultingactions– It is important to consider every possibleoutcome to ensure that you have overlookednothingFor more information aboutDecision Tables visitscsite.com/sad8e/more,locate Chapter 5 and thenthe Decision Tables link.Figure 5-35Figure 5-3635

Process Description Tools Decision Tables– The number of rules doubles each time youadd a condition– Can have more than two possible outcomes– Often are the best way to describe a complexset of conditionsFigure 5-3736

Process Description Tools Decision Trees– Graphical representation of the conditions,actions, and rules found in a decision table– Whether to use a decision table or tree oftenis a matter of personal preference– Is an effective way to describe a relativelysimple processFigure 5-38Figure 5-3937

Logical Versus Physical Models While structured analysis tools are used todevelop a logical model for a newinformation system, such tools also can beused to develop physical models of aninformation system A physical model shows how the system’srequirements are implemented38

Logical Versus Physical Models Sequence of Models– Many systems analysts create a physicalmodel of the current system and thendevelop a logical model of the currentsystem before tackling a logical model of thenew system– Performing that extra step allows them tounderstand the current system better39

Logical Versus Physical Models Four-Model Approach– Develop a physical model of the currentsystem, a logical model of the currentsystem, a logical model of the new system,and a physical model of the new system– The only disadvantage of the four-modelapproach is the added time and cost40

Chapter Summary During data and process modeling, a systemsanalyst develops graphical models to show howthe system transforms data into usefulinformation The end product of data and process modelingis a logical model that will support businessoperations and meet user needs Data and process modeling involves three maintools: data flow diagrams, a data dictionary,and process descriptions41

Chapter Summary Data flow diagrams (DFDs) graphically showthe movement and transformation of data inthe information system DFDs use four symbols A set of DFDs is like a pyramid with thecontext diagram at the top42

Chapter Summary The data dictionary is the centraldocumentation tool for structured analysis Each functional primitive process isdocumented using structured English, decisiontables, and decision trees Structured analysis tools can be used todevelop a logical model during one systemsanalysis phase, and a physical model during thesystems design phase43

Test Yourself1. A logical/physical model describes how thesystem will be constructed.44

Test Yourself1. A physical model describes how the systemwill be constructed.45

Test Yourself2. The following symbols are from theset. Name them:46

Test Yourself2. The following symbols are from theGane and Sarson set. Name them:Data StoreProcess47

Test Yourself3. Select the correct example ntAccountsReceivable48