Software Quality
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Transcript of Software Quality
Software Quality
Applied throughout SW Engineering Process Encompasses
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
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• 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) – # regions in flowchart V(G) – 10 is upper limit
Metrics
Process metrics 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• Mt - # modules in current release
• Fc - modules changed in current release
• Fa - # modules added
• Fd - # modules deleted
• SMI = 1 is GOOD.