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

21/08/58Quality Concept2 Content  How is measures quality?  Cost of quality  The quality triangle  Type of software quality

21/08/58Quality Concept3 How is measures quality?  Quality is frequently associated with some measure of :  Goodness,  Excellence  Luxury

21/08/58Quality Concept4 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: whata customer is willing to pay for quality.

21/08/58Quality Concept5 DefectsEffort User  Delivered defects  Wasted time Manufacturer  Defect injection rate  Defect removal efficiency  Defect prevention  Quality appraisal rework  Customer support  Complaint handling  Product recall  Warranty claims Product Number of defects Defect density  Rework  Scrap Value Cost of defective product  Cost of quality relate activities Table Of Quality Measures

21/08/58Quality Concept6 Cost of quality There are 2 major elements 1. The cost of quality improvement: associated with activities (Table 1)   Defect prevention   Appraisal 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

21/08/58Quality Concept7 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

21/08/58Quality Concept8 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

21/08/58Quality Concept9 Cost of Quality Curve 0% 100% Cost Quality

21/08/58Quality Concept10 The quality triangle  Products can suffer from poor quality in number of different ways:  User’s view  Product’s view  Manufacturer’s view

21/08/58Quality Concept11 The Quality Triangle Gap Product View product User Requirements User’s View Specification Manufacturer’s View

21/08/58Quality Concept12 User Requirement – Specification gap  Misunderstood requirements  Ignored requirements  Missing requirements  Outdated requirements  Unneeded requirements

21/08/58Quality Concept13 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

21/08/58Quality Concept14 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

21/08/58Quality Concept15 The Quality Triangle Product Specification User Requirements  If the quality better aligned the triangle will become smaller  If all view are perfectly aligned, it will be represented by a single dot.

21/08/58Quality Concept16 Quality triangle shapes

21/08/58Quality Concept17 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 meets REQ Poor understanding of REQ poor SW development : SW not meets REQ

21/08/58Quality Concept18 Software Product Measurement  In Table list a number of the more popular measures of Software Product quality In Table list a number of the more popular measures of Software Product quality In Table list a number of the more popular measures of Software Product quality  The ISO 9126 Standard for Software Product Quality

21/08/58Quality Concept19

21/08/58Quality Concept20 Software Quality  External Quality  Internal Quality  Quality in Use

21/08/58Quality Concept21 The Quality Triangle product User Requirements Specification External Quality Internal Quality Quality in Use