Session 9 Program Design - UI Open Coursewareocw.ui.ac.id/materials/12.01_FASILKOM/IKI81404T_-_Perancangan... · Session 9 Program Design Based on System Analysis & Design 2nd Edition

PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – UNIVERSITY OF INDONESIA

PERANCANGAN SISTEM INFORMASI

Session 9 Program Design

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

Session 9 Program DesignSession 9 Program Design

Based on System Analysis & Design 2nd EditionAuthors : Alan Dennis & Barbara Haley Wixom

Publisher : John Wiley & Sons

2PowerPoint Course Material for SCELE Graduate Program Information TechnologyFaculty of Computer Science – University of Indonesia

ObjectivesObjectives

Be able to create a structure chartBe able to write a program specificationUnderstand the use of pseudocodeBecome familiar with event-driven programming


Key DefinitionsKey Definitions

Program design - creating instructions for the programmers The top-down, modular approach - begin with the “big picture” and gradually add detailProgram design document – all structure charts and specifications needed by programmers to implement the system


STRUCTURE CHART


The Structure ChartThe Structure Chart

Important program design techniqueShows all components of code in a hierarchical format

SequenceSelectionIteration


Structure Chart ExampleStructure Chart Example


Structure Chart ElementsStructure Chart Elements

ModuleLibrary moduleLoopConditional lineData coupleControl coupleOff-page connectorOn-page connector


Building the Structure ChartBuilding the Structure Chart

Processes in the DFD tend to represent one module on the structure chart

Afferent processes – provide inputs to systemCentral processes – perform critical system operationsEfferent processes – handle system outputs

The DFD leveling can correspond to the structure chart hierarchy


Types of Structure ChartsTypes of Structure Charts

Transaction structure – control module calls subordinate modules, each of which handles a particular transaction

Many afferent processesFew efferent processesHigher up levels of structure chartUsing inputs to create a new output


Transaction StructureTransaction Structure


Types of Structure ChartsTypes of Structure Charts

Transform structure – control module calls several subordinate modules in sequenceEach subordinate performs a step in a process that transforms an input into an output

Few afferent processesMany efferent processesLower levels of structure chartCoordinates the movement of outputs


Transform StructureTransform Structure


Steps in Building the Structure ChartSteps in Building the Structure Chart

1. Identify top level modules and decompose them into lower levels

2. Add control connections3. Add couples4. Review and revise again and again until

complete


CD SELECTIONSCD SELECTIONS






Design GuidelinesDesign Guidelines

High quality structure charts result in programs that are modular, reusable and easy to implement.Measures include:

CohesionCouplingAppropriate levels of fan-in and fan-out


Types of CohesionTypes of Cohesion

Types of Cohesion

FunctionalSequentialCommunicationalProceduralTemporalLogicalCoincidental

What Would Be an Exampleof Each?


Example of Low CohesionExample of Low Cohesion

Logical Cohesion


Cohesion Decision TreeCohesion Decision Tree

Adapted from Page-Jones, 1980


FactoringFactoring

Process of dealing with “low” cohesionSeparates tasks into different modulesReduces use of control flags


Types of CouplingTypes of Coupling

Types of Coupling

DataStampControlCommonContent

What Would Be an Exampleof Each?

Good

Bad


Your TurnYour Turn

What, if anything, happens to coupling when you create modules that are more cohesive?What, if anything happens to the cohesiveness of modules when you lower the coupling among them?


Fan-inFan-in

High fan-in preferredPromotes reuse of subordinate modules

1.1CalculateEmployee

Salary

1.2Print

EmployeeRoster

1.3CalculateBenefits

2.1.1Read

EmployeeRecord

1.1CalculateEmployee

Salary

1.2Print

EmployeeRoster

1.3CalculateBenefits

1.1.1Read

EmployeeRecord

1.2.1Read

EmployeeRecord

1.3.1Read

EmployeeRecord

Low fan-in not preferred


Quality ChecklistQuality Checklist1. Library modules have been created where ever possible2. The diagram has a high fan-in structure3. Control modules have no more than 7 subordinates4. Each module performs only one function (high cohesion)5. Modules sparingly share information (loose coupling)6. Data couples that are passed are actually used by the

accepting module7. Control couples are passed from “low to high”8. Each module has a reasonable amount of code associated

with it


PROGRAM SPECIFICATION


Program Specifications ContentProgram Specifications Content

No standard approachInclude program informationNote events that trigger actionsList inputs and outputsInclude pseudocodePresent additional notes and comments


Program Specification FormProgram Specification Form


Pseudocode ExamplePseudocode Example

(Get CD-info module)Accept (CD_title) {Required}Accept (CD_artist) {Required}Accept (CD_category) {Required}Accept (CD_length)

Return


CASE Tool View of Process DescriptionCASE Tool View of Process Description


CD SELECTIONCD SELECTION


SummarySummaryThe structure chart shows all of the functional components needed in the program at a high level. Components of the structure chart show sequence, selection, and iterationFollow design guidelines regarding cohesion, coupling, and fan-in/fan-out.Prepare detailed specifications to programmers including pseudocode to show important programming structures.

Documents

Session 9 Program Design - UI Open Coursewareocw.ui.ac.id/materials/12.01_FASILKOM/IKI81404T_-_Perancangan... · Session 9 Program Design Based on System Analysis & Design 2nd Edition