INFORMATION SYSTEMS @ X INFO425: Systems Design Chapter 10 Traditional Approach to Design

INFORMATION SYSTEMS @ XINFORMATION SYSTEMS @ X

INFO425: Systems DesignINFO425: Systems Design

Chapter 10Chapter 10

Traditional Approach to DesignTraditional Approach to Design



Learning ObjectivesLearning Objectives

Describe the steps involved in the traditional approach Describe the steps involved in the traditional approach to designing the application architectureto designing the application architecture

Develop a system flowchartDevelop a system flowchart Develop a structure chart using transaction analysis and Develop a structure chart using transaction analysis and

transform analysistransform analysis Write pseudocode for structured modulesWrite pseudocode for structured modules Explain how to use three-layer design with the Explain how to use three-layer design with the

traditional approachtraditional approach



OverviewOverview

Traditional approach to designing softwareTraditional approach to designing software Overview of structured models, model development process, Overview of structured models, model development process,

related terminologyrelated terminology How data flow diagrams are annotated with automation How data flow diagrams are annotated with automation

boundary informationboundary information How analysis phase models are transformed into design How analysis phase models are transformed into design

models using system flowcharts, structure charts, and models using system flowcharts, structure charts, and module pseudocodemodule pseudocode

Integration into other design phase activitiesIntegration into other design phase activities Applying approach to a three-layer architectureApplying approach to a three-layer architecture



The Structured Approach to Designing The Structured Approach to Designing the Application Architecturethe Application Architecture

Application software programsApplication software programs Designed in conjunction with database and user interfaceDesigned in conjunction with database and user interface Hierarchy of modulesHierarchy of modules

Design internal logic of individual modulesDesign internal logic of individual modules Top-down approachTop-down approach

DFDs with automation boundariesDFDs with automation boundaries System flowcharts, structure charts, pseudocodeSystem flowcharts, structure charts, pseudocode



Structured Design ModelsStructured Design Models



The Automation System BoundaryThe Automation System Boundary

Partitions data flow diagram processes into Partitions data flow diagram processes into manual processes and automated systemsmanual processes and automated systems

Processes can be inside or outside boundaryProcesses can be inside or outside boundary Data flows can be inside and outside of boundaryData flows can be inside and outside of boundary

Data flows that cross system boundary represent inputs and Data flows that cross system boundary represent inputs and outputs of systemoutputs of system

Data flows that cross boundaries between programs Data flows that cross boundaries between programs represent program-to-program communication represent program-to-program communication



DFD with Automation System BoundaryDFD with Automation System Boundary (Figure 10-2)(Figure 10-2)



The System FlowchartThe System Flowchart

Representation of various computer programs, Representation of various computer programs, files, databases, and associated manual processes files, databases, and associated manual processes that make up complete systemthat make up complete system

Frequently constructed during analysis activitiesFrequently constructed during analysis activities Graphically describes organization of subsystems Graphically describes organization of subsystems

into automated and manual componentsinto automated and manual components Can show type of transaction processing systemCan show type of transaction processing system

BatchBatch Real-timeReal-time



Common System Flowchart SymbolsCommon System Flowchart Symbols



Sample System Flowchart for Payroll System Sample System Flowchart for Payroll System (Figure 10-4)(Figure 10-4)



The Structure ChartThe Structure Chart

Describes functions and sub-functions of each Describes functions and sub-functions of each part of systempart of system

Shows relationships between modules of a Shows relationships between modules of a computer programcomputer program

Simple and direct organization Simple and direct organization

Each module performs a specific functionEach module performs a specific function

Each layer in a program performs specific activitiesEach layer in a program performs specific activities

Chart is tree-like with root module and branchesChart is tree-like with root module and branches



A Simple Structure Chart for the A Simple Structure Chart for the Calculate Pay Amounts ModuleCalculate Pay Amounts Module



Structure Chart SymbolsStructure Chart Symbols



Structure Chart for Entire Payroll ProgramStructure Chart for Entire Payroll Program



Developing a Structure ChartDeveloping a Structure Chart

Transaction analysisTransaction analysis Uses system flow chart and event table inputsUses system flow chart and event table inputs Upper-level modules developed firstUpper-level modules developed first Identifies each transaction supported by programIdentifies each transaction supported by program

Transform analysisTransform analysis Uses DFD fragments for inputsUses DFD fragments for inputs Computer program “transforms” inputs into outputsComputer program “transforms” inputs into outputs Charts have input, calculate, and output sub-treesCharts have input, calculate, and output sub-trees



High-Level Structure Chart for the Order-Entry High-Level Structure Chart for the Order-Entry Subsystem After Transaction AnalysisSubsystem After Transaction Analysis



Steps to Create a Structure Chart Steps to Create a Structure Chart from a DFD Fragmentfrom a DFD Fragment

Determine primary information flowDetermine primary information flow Main stream of data transformed from some input form to Main stream of data transformed from some input form to

output formoutput form

Find process that represents most fundamental Find process that represents most fundamental change from input to outputchange from input to output

Redraw DFD with inputs to left and outputs to right Redraw DFD with inputs to left and outputs to right – – central transformcentral transform process goes in middle process goes in middle

Generate first draft of structure chart based on Generate first draft of structure chart based on redrawn data flowredrawn data flow



The The Create New OrderCreate New Order DFD Fragment DFD Fragment



Decomposed DFD for Decomposed DFD for Create New OrderCreate New Order



Rearranged Rearranged Create New OrderCreate New Order DFD DFD



First Draft of the Structure Chart for First Draft of the Structure Chart for Create New OrderCreate New Order (Figure 10-14)(Figure 10-14)



Steps to Create a Structure Chart from a DFD Steps to Create a Structure Chart from a DFD Fragment Fragment ((continuedcontinued))

Add other modules Add other modules Get input data via user-interface screensGet input data via user-interface screens Read from and write to data storageRead from and write to data storage Write output data or reports Write output data or reports

Add logic from structured English or decision Add logic from structured English or decision tablestables

Make final refinements to structure chart based on Make final refinements to structure chart based on quality control conceptsquality control concepts



The Structure Chart for the The Structure Chart for the Create New OrderCreate New Order Program Program (Figure 10-15)(Figure 10-15)



Combination Combination of Structure of Structure

Charts: Charts: Transaction Transaction

and and Transform Transform AnalysisAnalysis



Evaluating the Quality of a Structure ChartEvaluating the Quality of a Structure Chart

Module coupling Module coupling Measure of how module is connected to other modules in Measure of how module is connected to other modules in

programprogram Goal is to be loosely coupled (independent)Goal is to be loosely coupled (independent)

Module cohesionModule cohesion Measure of internal strength of moduleMeasure of internal strength of module Module performs one defined taskModule performs one defined task Goal is to be highly cohesiveGoal is to be highly cohesive



Module Algorithm DesignModule Algorithm Design——PseudocodePseudocode

Describes internal logic of software modulesDescribes internal logic of software modules Variation of structured English that is closer to Variation of structured English that is closer to

programming codeprogramming code Syntax should mirror development languageSyntax should mirror development language Three types of control statements used in Three types of control statements used in

structured programmingstructured programming SequenceSequence –– sequence of executable statements sequence of executable statements Decision Decision –– if-then-else logic if-then-else logic Iteration Iteration –– do-until or do-while do-until or do-while



Integrating Structured Application Design with Integrating Structured Application Design with Other Design TasksOther Design Tasks

Structure chart must be modified or enhanced to Structure chart must be modified or enhanced to integrate design of integrate design of user interfaceuser interface and and databasedatabase

Are additional Are additional modulesmodules needed? needed? Does Does pseudocodepseudocode in modules need modification? in modules need modification? Are additional Are additional data couplesdata couples needed to pass data? needed to pass data?

Structure charts and system flowcharts must Structure charts and system flowcharts must correspond to planned correspond to planned network architecturenetwork architecture

Required protocols, capacity, and securityRequired protocols, capacity, and security



Three-Layer DesignThree-Layer Design

Three-layer architectureThree-layer architecture

View layer, business logic layer, and data layerView layer, business logic layer, and data layer

Structure charts and system flowcharts describe Structure charts and system flowcharts describe design decisions and software structuring design decisions and software structuring

Employs multiple programs for user interface, Employs multiple programs for user interface, business logic, and data access modulesbusiness logic, and data access modules

Modules in different layers communicate over real-Modules in different layers communicate over real-time links using well-defined protocolstime links using well-defined protocols



System Flowchart Showing Three-Layer System Flowchart Showing Three-Layer Architecture for Customer OrderArchitecture for Customer Order



Structure Chart Showing Three-Layer Architecture for Structure Chart Showing Three-Layer Architecture for Create New Order Create New Order (Figure 10-20)(Figure 10-20)

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INFORMATION SYSTEMS @ X INFO425: Systems Design Chapter 10 Traditional Approach to Design