Quality Concept Computer Science Department Faculty Of Science

Quality Concept Computer Science Department, Faculty Of Science Prince of Songkhla University Apirada Thadadech

Content § § How is measures quality? Cost of quality The quality triangle Type of software quality 9/30/2020 Quality Concept 2

How is measures quality? § Quality is frequently associated with some measure of : § Goodness, § Excellence § Luxury 9/30/2020 Quality Concept 3

How is measures quality? (next) There are 4 other, equally valid perspectives: 1. The user’ s perspective : Product is fitness for requirements. 2. The manufacturer’s : how well a product conform to specification. 3. The product perspective: measurable attributes of a product. 4. The value-based perspective: what a customer is willing to pay for quality. 9/30/2020 Quality Concept 4

Table Of Quality Measures Defects Effort User §Delivered defects §Wasted time Manufacturer §Defect injection rate §Defect removal efficiency Product Number of defects Defect density §Defect prevention §Quality appraisal rework §Customer support §Complaint handling §Product recall §Warranty claims §Rework §Scrap Value Cost of defective product 9/30/2020 Quality Concept §Cost of quality relate activities 5

Cost of quality There are 2 major elements 1. The cost of quality improvement: associated with activities (Table 1) § § 2. Defect prevention Appraisal The cost of failure : fails to meet its quality requirements (Table 2) § § 9/30/2020 Internal failure – prior to transfer of ownership to the customer External failure – after transfer of ownership to the customer Quality Concept 6

Table 1 Typical quality improvement costs Defect Prevention Appraisal §Quality planning §Quality auditing §Reviewing & verifying designs §Quality training §Acquisition, Analysis and report of quality data §Product recall insurance §Design appraisal §Receiving and inspection §Inspection and testing §Analysis and reporting of test and inspection results §Record storage of quality documents 9/30/2020 Quality Concept 7

Table 2 Typical quality failure costs Internal Failure External Failure §Scrap §Replacement, rework and repair §Defect diagnosis §Downtime §Complaints §Support §Warranty claims §Products rejected and returned §Concessions §Loss of sales §Recall costs §Product reliability 9/30/2020 Quality Concept 8

Cost of Quality Curve 0% 9/30/2020 Quality Concept 100% 9

The quality triangle § Products can suffer from poor quality in number of different ways: § User’s view § Product’s view § Manufacturer’s view 9/30/2020 Quality Concept 10

The Quality Triangle Product View product Gap User Requirements User’s View 9/30/2020 Specification Quality Concept Manufacturer’s View 11

User Requirement – Specification gap § § § Misunderstood requirements Ignored requirements Missing requirements Outdated requirements Unneeded requirements 9/30/2020 Quality Concept 12

Specification – Product Gap § Wrong interpretation of requirement cause of ambiguity in specification § Requirements identified after development commented § Changes to specified requirements identified after development commented § Features added by the developers follow technical § Requirements ignored by the developers cause of they were too difficult to implement 9/30/2020 Quality Concept 13

Product – User Requirement Gap § The gap is directly dependent on 2 side of triangle § If two sides are short, then this gap will be small § If two sides are long, then this gap will be large 9/30/2020 Quality Concept 14

The Quality Triangle Product § If the quality better aligned the triangle will become smaller ts n e m e r i u q e R r e Us 9/30/2020 Spe cific ation § If all view are perfectly aligned, it will be represented by a single dot. Quality Concept 15

Quality triangle shapes 9/30/2020 Quality Concept 16

Quality triangle shapes Poor understanding of REQ. corrected during SW development : SW meets REQ Good understanding of REQ. poor SW development : SW not meets REQ Poor understanding of REQ good SW development : SW not poor SW development : SW not meets REQ 9/30/2020 Quality Concept 17

Software Product Measurement § In Table list a number of the more popular measures of Software Product quality § The ISO 9126 Standard for Software Product Quality 9/30/2020 Quality Concept 18

9/30/2020 Quality Concept 19

Software Quality § § § External Quality Internal Quality in Use 9/30/2020 Quality Concept 20

The Quality Triangle External Quality product Internal Quality in Use Specification User Requirements 9/30/2020 Quality Concept 21