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

Product Operation Product Revision Product Transition Maintainability Flexibility Testability Portability Reusability Interoperability Correctness Reliability Usability Integrity Efficiency

History Sole responsibility of craftsman 1916 Bell Labs – 1 st formal QA 1970s Military standards for SQA SQA groups – in house representatives ISO , 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 (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.