Software Quality
Engineering
Chapters 1-3
Overview, Software Quality and Quality
Assurance
Ch.1: Overview and Basics
General Book Information
 Quality: View/Measure/Model
 QA Activities/Alternatives
 From QA to SQE
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Ch.1: Main Problems Addressed
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Deliver software system that...
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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:
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Size: MLOC products common
Complexity
Environmental stress/constraints
Flexibility/adaptability expected
no silver bullet", but...SQE (software quality engineering)
helps
Ch.1: SQE as Answer
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Major SQE activities:
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Testing: remove defect & ensure quality
Other QA alternatives to testing
How do you know: analysis & modeling
Scope and content hierarchy: Fig.1.1
Ch.1: Book Contents
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QA alternatives/activities:
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Testing (Part II)
Other alternatives (Part III):
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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
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Applicability and effectiveness
Dealing with quality problems/defects:
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prevention/removal/tolerance
Cost
Improvement (Part IV).
Ch.2: General Quality Views
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In Kitchenham & Pfleeger (1996):
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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):
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Quality defined by Conformance/adaptability/innovation
Traditional: conformance only
Evolved to include service, manage expectations:
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0 defects -> 0 defections in customers
Domain specific (for info age?):
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specificity, stability, evolvability
-ilities
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User quality expectations
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Performs right functions (correctness)
reliability
usability
Install-ability
inter-operability
adaptability
cost
Producer quality expectations
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fulfill contractual obligations
Modifiability (flexibility)
maintainability
portability
profitability
Ch.2: Quality Frameworks
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Focus in various frameworks/mega-models different
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ISO 9126 top-level quality characteristics (pg. 18):
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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
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.
Ch.2: Defining Quality
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Quality: views
and attributes
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SQE focus:
correctnessrelated
Ch.2: Defect and Quality
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Defect definition – a problem with the software, either
with its external behavior or internal characteristics
 Failure: external behavior
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Fault: internal characteristics
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cause for failures
Error: incorrect/missing human action
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deviation from expected behavior as specified
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)
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Defect handling/resolution: Chapter 4.
Ch.3: QA: Dealing with Defects
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QA: quality assurance
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Classification schemes to deal with defects:
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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
Prevention – error blocking or error source removal
Removal (detect them first)
Containment
Classification illustrated: Fig 3.1 (p.30)
Ch.3: Error/Fault/Failure & QA
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Preventing fault injection
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Causal/statistical/etc. analyses based
Preventive measures:
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Formal methods: formal verification (faults absent)
Removal of faults
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education, technology, process, tools
Inspection: faults discovered
Testing: failures trace back to faults
Tolerance of faults
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Local fault does not imply global failure
Dynamic containment measures to tolerate faults
Ch.3: Defect Prevention Overview
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Error blocking
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Error source removal
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Error: missing/incorrect actions
Direct intervention
Error blocked => fault injections prevented
Rely on technology/tools/etc.
Root cause analysis =>identify error sources
Removal through education/training/etc.
Details: Chapter 13.
Ch.3: Defect Prevention: Formal
Verification Overview
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Motivation
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Fault present:
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Fault absent: formally verify.
Basic ideas
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Behavior formally specified:
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pre/post conditions, or
as mathematical functions.
Verify “correctness":
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revealed through testing/inspection/etc.
intermediate states/steps,
axioms and compositional rules.
Approaches: axiomatic/functional/etc.
Details: Chapter 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
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Ch.3: Defect Reduction: Inspection
Overview
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Artifacts (code/design/test-cases/etc.) from
requirements/design/coding/testing/etc. phases.
Informal reviews:
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Formal inspections:
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Self conducted reviews.
Independent reviews.
Orthogonality of views desirable.
Fagan inspection and variations.
Process and structure.
Individual vs. group inspections.
What/how to check: techniques .
Details: Chapter 14.
Ch.3: Defect Reduction: Testing
Overview
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Product/Process characteristics:
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What to check:
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Verification vs validation
External specifications (black-box)
Internal implementation (white/clear-box)
Criteria: when to stop?
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Object: product type, language, etc.
Scale/order: unit, component, system, …
Who: self, independent, 3rd party
Coverage of specs/structures.
Reliability => usage-based testing techniques
Much, much more in Part II.
Ch.3: Defect Containment: Fault
Tolerance Overview
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Motivation
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Fault present but removal infeasible/impractical
Fault tolerance => contain defects
FT techniques: break fault-failure link
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Recovery: rollback and redo
NVP: N-version programming
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fault blocked/out-voted
Details: Chapter 16.
Need to know these for future questions
and Master’s exam
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What are 11 major software quality
factors?
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What are seven software quality assurance
activities?
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What is the difference between verification
and validation?
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
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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
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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.)
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Discussion Questions
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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?________________
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Which of the 11 software quality factors concern product
revision, which concern product operation and which
concern product transition?
revision
transition
operation
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Article – Fill in Figure 1.