Software Quality Engineering

1. Software Quality Engineering Chapters 1-3 Overview, Software Quality and Quality Assurance

2. Ch.1: Overview and Basics • General Book Information • Quality: View/Measure/Model • QA Activities/Alternatives • From QA to SQE

3. Ch.1: Main Problems Addressed • Deliver software system that... • does what it is supposed to do. • does the things correctly. • respectively validate and verify software system to show/demonstrate/prove it (“does"). • Major difficulties for the above: • Size: MLOC products common • Complexity • Environmental stress/constraints • Flexibility/adaptability expected • no silver bullet", but...SQE (software quality engineering) helps

4. Ch.1: SQE as Answer • Major SQE activities: • Testing: remove defect & ensure quality • Other QA alternatives to testing • How do you know: analysis & modeling • Scope and content hierarchy: Fig.1.1

5. Ch.1: Book Contents • QA alternatives/activities: • Testing (Part II) • Other alternatives (Part III): • defect prevention (Ch.13) • inspection, review, analysis (Ch.14) • formal verification (Ch.15) • defect containment (Ch.16) • Analysis and improvement (Part IV) • Issues in different QA alternative • Applicability and effectiveness • Dealing with quality problems/defects: • prevention/removal/tolerance • Cost • Improvement (Part IV).

6. Ch.2: General Quality Views • In Kitchenham & Pfleeger (1996): • Transcendental view: hard to define, but recognized • User view: fitness for purpose or meet user’s needs • Manufacturing view: conform to process standards • Product view: inherent product characteristics. • Value-based view: customers’ willingness to pay. • In Prahalad & Krishnan (1999): • Quality defined by Conformance/adaptability/innovation • Traditional: conformance only • Evolved to include service, manage expectations: • 0 defects -> 0 defections in customers • Domain specific (for info age?): • specificity, stability, evolvability

7. -ilities • User quality expectations • Performs right functions (correctness) • reliability • usability • Install-ability • inter-operability • adaptability • cost • Producer quality expectations • fulfill contractual obligations • Modifiability (flexibility) • maintainability • portability • profitability

8. Ch.2: Quality Frameworks • Focus in various frameworks/mega-models different • McCall: factors, criteria, and metrics • Basili: GQM (goal-question-metric) • SEI/CMM: process / levels of maturity • ISO 9000: series of standards • Dromey: component reflects quality-attributes • ISO 9126 top-level quality characteristics (pg. 18): • Functionality: what is needed? • Reliability: function correctly. • Usability: effort to use. • Efficiency: resources needed. • Maintainability: correct/improve/adapt. • Portability: one environment to another. • Alternative frameworks: company-specific, web-based, etc.

9. Ch.2: Defining Quality • Quality: views and attributes • SQE focus: correctness-related

10. Ch.2: Defect and Quality • Defect definition – a problem with the software, either with its external behavior or internal characteristics • Failure: external behavior • deviation from expected behavior as specified • Fault: internal characteristics • cause for failures • Error: incorrect/missing human action • conceptual mistakes • Bug/debug: avoid problematic terms, use instead defect detection and removal • Causal relations (not necessarily 1-1): errors => faults => failures: See Fig 2.1 (p.21) • Defect handling/resolution: Chapter 4.

11. Ch.3: QA: Dealing with Defects • QA: quality assurance • Focus on correctness aspect of quality • QA as dealing with defects. • Many activities: testing & others • How QA alternatives deal with defects => classification of QA alternatives • Classification schemes to deal with defects: • Prevention – error blocking or error source removal • Removal (detect them first) • Containment • Classification illustrated: Fig 3.1 (p.30)

12. Ch.3: Error/Fault/Failure & QA • Preventing fault injection • Causal/statistical/etc. analyses based • Preventive measures: • education, technology, process, tools • Formal methods: formal verification (faults absent) • Removal of faults • Inspection: faults discovered • Testing: failures trace back to faults • Tolerance of faults • Local fault does not imply global failure • Dynamic containment measures to tolerate faults

13. Ch.3: Defect Prevention Overview • Error blocking • Error: missing/incorrect actions • Direct intervention • Error blocked => fault injections prevented • Rely on technology/tools/etc. • Error source removal • Root cause analysis =>identify error sources • Removal through education/training/etc. • Details: Chapter 13.

14. Ch.3: Defect Prevention: Formal Verification Overview • Motivation • Fault present: • revealed through testing/inspection/etc. • Fault absent: formally verify. • Basic ideas • Behavior formally specified: • pre/post conditions, or • as mathematical functions. • Verify “correctness": • intermediate states/steps, • axioms and compositional rules. • Approaches: axiomatic/functional/etc. • Details: Chapter 15.

15. Ch3: Other Defect Prevention Techniques • Appropriate use of software methodologies and technologies • Use of information hiding principle and abstraction and modularization • Better managed processes • Enforcement of standards • Use of tools

16. Ch.3: Defect Reduction: Inspection Overview • Artifacts (code/design/test-cases/etc.) from requirements/design/coding/testing/etc. phases. • Informal reviews: • Self conducted reviews. • Independent reviews. • Orthogonality of views desirable. • Formal inspections: • Fagan inspection and variations. • Process and structure. • Individual vs. group inspections. • What/how to check: techniques . • Details: Chapter 14.

17. Ch.3: Defect Reduction: Testing Overview • Product/Process characteristics: • Object: product type, language, etc. • Scale/order: unit, component, system, … • Who: self, independent, 3rd party • What to check: • Verification vs validation • External specifications (black-box) • Internal implementation (white/clear-box) • Criteria: when to stop? • Coverage of specs/structures. • Reliability => usage-based testing techniques • Much, much more in Part II.

18. Ch.3: Defect Containment: Fault Tolerance Overview • Motivation • Fault present but removal infeasible/impractical • Fault tolerance => contain defects • FT techniques: break fault-failure link • Recovery: rollback and redo • NVP: N-version programming • fault blocked/out-voted • Details: Chapter 16.

19. Need to know these for future questions and Master’s exam • What are 11 major software quality factors? • What are seven software quality assurance activities? • What is the difference between verification and validation?

20. 11 Major Quality Factors • Correctness – meets specs and objectives • Reliability – perform intended function with required precision (includes robustness) • Efficiency - amount of code and resources • Integrity – controlled access • Usability – effort required to learn/operate

21. Quality Factors cont. • Maintainability – ease locate/fix error • Flexibility (modifiability) – ease to modify operational program • Testability – ease to test • Portability – works in other environments • Interoperability – works with other systems • Reusability – ease of reuse

22. 7 Activities • Application of technical methods and tools (to ensure QA) • Formal technical reviews • Software testing • Enforcement of standards to process • Control of change (configuration management) • Measurement (product and process) • Record keeping and reporting (information for reviews, etc.)

23. Discussion Questions • What is essential (but not sufficient) to earn the assessment that the software is dependable? _____________ Other than that, what should we put greater emphasis on to attain high quality software?________________ • Which of the 11 software quality factors concern product revision, which concern product operation and which concern product transition? revision transition operation • Article – Fill in Figure 1.