Software Quality

1
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

2
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.)

3
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

4
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

5
Product Operation
Portability Reusability Interoperability
Maintainability Flexibility Testability
Product Revision
Product Transition
Correctness Reliability Usability Integrity
Efficiency
6
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
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.)

8
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)

9
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)
• Halsteads metrics
• Based on operators and operands
• McCabes Cyclomatic Complexity (product metric)
• V(G) regions in flowchart lt 10 is upper
  limit

10
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 (w1D1 ..w6D6)

11
Metrics

• Halsteads product metrics
• n1 - distinct operators
• n2 - distinct operands
• N1 - of operators
• N2 - of operands
• VERY primitivehavent been shown to be useful
• McCabes Cyclomatic Complexity (product metric)
  
• regions in flowchart
• V(G) 10 is upper limit

12
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

13
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.