Quality Assurance

1
Quality Assurance

• With the narrower and correctness-centered
  definition of quality, we can classify QA s
  generic roles as participants in
• Defect Prevention
• Defect Reduction/Removal
• Defect Containment

2
QAs Roles in Prevention/Reduction/Containment of
Defects
Failures
Fl1 Fl2 Fl3 Fl4 Fl5
Errors
E1 E2 E3 E4
Faults
F1 F2 F3
2. Reduction thru Fault removal
1. Prevention thru Error blocking removal
3. Containment of failures
Preventing defect from escaping into execution
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1. Defect Prevention

• Root-Cause Based Defect Prevention Activities
• Human Misconception or Lack of Knowledge - (root
  cause)
• Education/training - (prevention)
• Imprecise Requirements, Design and
  Implementation, and Testing
• Improved or formal methodologies
• Non-conformance in Process or Standards
• Process and standard enforcements
• Lack of Technology or Tools
• Adoption of appropriate technology and tools

4
Education/Training

• People are the most relevant factor in software
  development and support. Thus educating and
  training people will support the prevention of
  errors
• Domain specific and product specific knowledge
• Software development support knowledge
• Software process knowledge
• Software methodology, technology, and tool
  knowledge

same
5
Improved and Formal Methods

• Specifications of requirements and of design are
  predecessor artifacts to coding, thus preventions
  of errors in these specifications can greatly
  prevent coding errors and affect code and
  execution quality.
• Defining pre-conditions and post-conditions
• Proof of correctness (formal verification)
• Specification languages such as Z, suite of UML
  notations, ERD diagrams, etc.

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Process, Technology and Tools

• Better defined process and enforced/managed
  process puts discipline into software development
  /support and that can prevent errors.
• Improved technology and methods such as
  modularization, information hiding, re-use of
  patterns, etc. can help in preventing errors in
  design and development.
• Improved software tools such as development
  platform that provides code frameworks and
  dynamic syntax checker/editor helps in preventing
  errors

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2. Defect Reduction

• It is not possible to have a 100 effective error
  prevention activity. Thus we need to perform
  fault removal to get defect reduction
• Inspection/Review
• Testing
• Other techniques Prototyping, Simulation, Fault
  Tree Analysis, risk identification

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Inspections (covered in
Lesson 12)

• Less formal ones include walkthrough and reviews
• Most successful one is the formal Fagan
  Inspection methodology which includes multiple
  steps conducted by a team of inspectors
• Identification and assignment of moderator and
  inspectors
• Moderator prepares for the inspection inspectors
  prepares for the inspection (different
  preparations)
• Actual reading/inspection of the material by
  inspectors --- possibly with the author in
  attendance
• Recording of the faults found, of severity status
  assigned, of fix target and schedule by moderator
• Fault fixes tracked and inspection report
  completed by moderator

9
Testing

• Testing involves
• Development of test cases
• Execution of the test cases
• Observing the software behavior
• Recording and reporting the results
• Different phases of testing
• Unit testing
• Functional and component testing
• Integration testing
• System testing
• User acceptance testing / beta testing

My additions
10
Testing (cont.)

• Two major types of Testing
• Black Box testing (external functionality and
  property testing) where we generate test
  scenarios mostly from requirements .
• White Box (internal structure and data path
  testing) testing where we generate test cases
  from the design and code.
• Testing Completion
• Based on coverage of test cases test
  scenarios
• Based on pre-set reliability or quality goals

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Other Defect Reduction Related Techniques

• Symbolic Execution, Simulation and Prototyping at
  the early phases of software development
• In-Process analysis with fault-tree or
  cause-effect tree
• Use design/code complexity, size, change
  history to focus on high potential error-prone
  areas

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3. Defect Containment

• In some systems such as medical, nuclear
  equipment, or aerospace industries even a
  little number of defects that escaped through
  prevention and reduction can be extremely harmful
• We need to contain the failures by reducing the
  resulting damage

13
Fault Tolerance

• Fault tolerance originated with hardware systems
  with spare parts and back-up capabilities.
• Software we use the same concept
• Recovery blocks a section of the code or
  software is re-executed after a failure occurs
  and after some parameters are re-set.
• N-Version Programming execution of several same
  functionality programs in parallel, thus a
  program failure may be localized and possibly
  by-passed

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Safety Critical

• Safety is a key characteristic of medical,
  nuclear, industrial, transportation and many
  other types of systems. Thus we view it from a
  containment perspective also
• After Hazard Prevention and Hazard Reduction of
  errors and faults, we need to be able to
  separate out or lockout the defective parts
  at containment time.
• Hazard Control and Damage Control are post
  accident activities of preventing the damage from
  further spreading and causing more than the
  original harm.