Software Quality
• Applied throughout SW Engineering Process
• Encompasses
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Analysis, design, coding, testing, tools
Formal tech reviews
Multi-tiered testing strategy
Control of Software documents
Appliance to standards
Measurement and reporting mechanisms
Definition
• Conformance to explicitly stated functional and
performance requirements, explicit standards, and
implicit characteristics expected of all
professionally developed software
▫ Requirements are foundation
▫ Follow standards for development of software
▫ Implicit requirements (user-friendliness,
maintainability, etc.)
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
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
Portability
Reusability
Interoperability
Maintainability
Flexibility
Testability
Product Operation
Correctness Reliability Usability Integrity Efficiency
History
• Sole responsibility of craftsman
• 1916 Bell Labs – 1st formal QA
• 1970s Military standards for SQA
• SQA groups – in house representatives
• ISO 9000-9001, SEI CMM
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.)
Software Reviews
• Filter
• Replace unit testing
• Catch 75% of design flaws prior to coding
• Reduces costs in subsequent steps
• Formal technical reviews (meeting of 4-5
people with roles, agenda,…)
• Inspections (outside group of people)
Software Quality Metrics
• Measure a qualitative factor (efficiency,
maintainability, …etc.)
• Quantitative assessment
• Product Metrics
• Examples:
▫ IEEE Standard 982.1 (1988)
▫ Air Force DSQI (Design structure quality index)
▫ Halstead’s metrics
 Based on # operators and operands
▫ McCabe’s Cyclomatic Complexity (product metric)
 V(G) = # regions in flowchart < 10 is upper limit
DSQI:
▫ S1 - #modules defined in program architecture
▫ S3 - #modules whose correct function depends on
prior processing
▫ D1 – 0 if no distinct method used to design, otw 1
▫ D2 – 1 – (S1/S2)
▫ DSQI = sum (w1*D1 ..w6*D6)
Metrics
• Halstead’s product metrics
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n1 - # distinct operators
n2 - # distinct operands
N1 - # of operators
N2 - # of operands
VERY primitive…haven’t been shown to be useful
• McCabe’s Cyclomatic Complexity (product metric)
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▫ # regions in flowchart
▫ V(G) – 10 is upper limit
Metrics
• Process metrics
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Number of defects found in review, testing, release
Number of changes made to code to fix bug
Number of modules changed to fix bug
Rate at which bugs are found in testing…
Etc…
• Software Maturity Index
▫ Based on # modules in current release and # modules
changed, added, deleted in current release
Software Maturity Index
▫ SMI = [ Mt – (Fa + Fc + Fd)] / Mt where
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Mt - # modules in current release
Fc - modules changed in current release
Fa - # modules added
Fd - # modules deleted
SMI = 1 is GOOD.