Quality ConceptQuality Concept

Computer Science Department, Faculty Of Science Computer Science Department, Faculty Of Science Prince of Songkhla UniversityPrince of Songkhla University

Apirada ThadadechApirada Thadadech

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ContentContent

How is measures quality?How is measures quality? Cost of qualityCost of quality The quality triangleThe quality triangle Type of software qualityType of software quality

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How is measures quality?How is measures quality?

Quality is frequently associated with some Quality is frequently associated with some measure of :measure of : Goodness, Goodness, Excellence Excellence LuxuryLuxury

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How is measures quality?How is measures quality?(next)(next)

There are 4 other, equally valid perspectives:There are 4 other, equally valid perspectives:1.1. The user’ s perspective : Product is fitness for The user’ s perspective : Product is fitness for

requirements.requirements.2.2. The manufacturer’s : how well a product The manufacturer’s : how well a product

conform to specification.conform to specification.3.3. The product perspective: measurable The product perspective: measurable

attributes of a product.attributes of a product.4.4. The value-based perspective: whatThe value-based perspective: what a a

customer is willing to pay for quality.customer is willing to pay for quality.

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DefectsDefects EffortEffort

UserUser Delivered defectsDelivered defects Wasted timeWasted time

ManufacturerManufacturer Defect injection rateDefect injection rateDefect removal efficiencyDefect removal efficiency

Defect preventionDefect preventionQuality appraisal reworkQuality appraisal reworkCustomer supportCustomer supportComplaint handlingComplaint handlingProduct recallProduct recallWarranty claimsWarranty claims

ProductProduct Number of defectsNumber of defects

Defect densityDefect density

ReworkReworkScrapScrap

ValueValue Cost of defective productCost of defective product Cost of quality relate Cost of quality relate activitiesactivities

Table Of Quality Measures

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Cost of qualityCost of qualityThere are 2 major elementsThere are 2 major elements1.1. The cost of quality improvement: associated with activities (Table 1) The cost of quality improvement: associated with activities (Table 1)

Defect prevention

Appraisal

2.2. The cost of failure : fails to meet its quality requirements (Table 2)The cost of failure : fails to meet its quality requirements (Table 2)

Internal failure – prior to transfer of ownership to the customer

External failure – after transfer of ownership to the customer

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Table 1 Typical quality improvement costsTable 1 Typical quality improvement costs

Defect PreventionDefect Prevention AppraisalAppraisal

Quality planningQuality planningQuality auditingQuality auditingReviewing & verifying Reviewing & verifying designsdesignsQuality trainingQuality trainingAcquisition, Analysis and Acquisition, Analysis and report of quality datareport of quality dataProduct recall insuranceProduct recall insurance

Design appraisalDesign appraisalReceiving and inspectionReceiving and inspectionInspection and testingInspection and testingAnalysis and reporting of test Analysis and reporting of test and inspection resultsand inspection resultsRecord storage of quality Record storage of quality documentsdocuments

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Table 2 Typical quality failure costsTable 2 Typical quality failure costs

Internal FailureInternal Failure External FailureExternal Failure

ScrapScrapReplacement, rework Replacement, rework and repairand repairDefect diagnosisDefect diagnosisDowntimeDowntime

ComplaintsComplaintsSupportSupportWarranty claimsWarranty claimsProducts rejected and Products rejected and returnedreturnedConcessionsConcessionsLoss of salesLoss of salesRecall costsRecall costsProduct reliabilityProduct reliability

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Cost of Quality CurveCost of Quality Curve

0%0% 100%100%

Cos

tC

ost

QualityQuality

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The quality triangleThe quality triangle

Products can suffer from poor quality in Products can suffer from poor quality in number of different ways:number of different ways: User’s viewUser’s view Product’s viewProduct’s view Manufacturer’s viewManufacturer’s view

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The Quality TriangleThe Quality Triangle

GapGap

Product View

product

User Requirements

User’s View

Specification

Manufacturer’s View

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User Requirement – Specification gapUser Requirement – Specification gap

Misunderstood requirementsMisunderstood requirements Ignored Ignored requirementsrequirements Missing requirementsMissing requirements Outdated requirementsOutdated requirements Unneeded requirementsUnneeded requirements

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Specification – Product GapSpecification – Product Gap

Wrong interpretation of requirement cause of Wrong interpretation of requirement cause of ambiguity in specificationambiguity in specification

Requirements identified after development Requirements identified after development commentedcommented

Changes to specified requirements identified Changes to specified requirements identified after development commentedafter development commented

Features added by the developers follow Features added by the developers follow technicaltechnical

Requirements ignored by the developers cause Requirements ignored by the developers cause of they were too difficult to implementof they were too difficult to implement

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Product – User Requirement GapProduct – User Requirement Gap

The gap is directly dependent on 2 side The gap is directly dependent on 2 side of triangleof triangle If two sides are short, then this gap will be If two sides are short, then this gap will be

smallsmall

If two sides are long, then this gap will be If two sides are long, then this gap will be largelarge

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The Quality TriangleThe Quality Triangle

Pro

duct

Pro

duct

Specification

Specification

User

User R

equirements

Requirements

If the quality better If the quality better aligned the triangle aligned the triangle will become smallerwill become smaller

If all view are If all view are perfectly aligned, it perfectly aligned, it will be represented will be represented by a single dot. by a single dot.

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Quality triangle shapesQuality triangle shapes

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Quality triangle shapesQuality triangle shapes

Poor understanding of REQ. Poor understanding of REQ. corrected during SW corrected during SW development :SW meets REQdevelopment :SW meets REQ

GoodGood understanding of REQ. understanding of REQ. poor SW development : SW not poor SW development : SW not meets REQmeets REQ

Poor understanding of REQPoor understanding of REQ

good SW development : SW good SW development : SW not meets REQnot meets REQ

Poor understanding of REQPoor understanding of REQ

poor SW development : SW not poor SW development : SW not meets REQmeets REQ

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Software Product MeasurementSoftware Product Measurement

In Table list a number of the more popular measures of Software Product quality

The ISO 9126 Standard for Software The ISO 9126 Standard for Software Product QualityProduct Quality

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Software QualitySoftware Quality

External QualityExternal Quality Internal QualityInternal Quality Quality in UseQuality in Use

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The Quality TriangleThe Quality Triangle

product

User RequirementsUser Requirements SpecificationSpecification

External External QualityQuality

Internal Internal QualityQuality

Quality in Use