Software Quality Assurance

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Software Quality Assurance
Computer Science 370 Evans J. Adams
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Software Quality

• A program that does not work is undoubtedly
  wrong, but a program that does work is not
  necessarily right. Michael Jackson

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Working is Not a Synonym for Quality

• Would you rather have a working program that is
  unmaintainable or a maintainable program that
  is not working???
• Remember Software Rots

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Product Quality

• What is quality?
• Where is quality?
• SQA Objectives

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What is Quality? (1)Operations Dimension

• Correctness (Does it do what I want?)
• Reliability (Does it do it accurately all of the
  time?)
• Efficiency (Will it run on my hardware as well as
  it can?)
• Integrity (Is it secure?)
• Usability (Can I run it?)

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What is Quality? (2)Transition Dimension

• Portability (Will I be able to use it on another
  machine?)
• Reusability (Will I be able to reuse some of the
  software?)
• Interoperability (Will I be able to interface it
  with another system?)

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What is Quality? (3)Revision Dimension

• Maintainability (Can I fix it?)
• Flexibility (Can I change it?)
• Testability (Can I test it?)

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Definition of Quality

• Crosby, Philip B., Quality is Free, The Art of
  Making Quality Certain, New American Library, New
  York, 1979, page 15.
• That is precisely the reason we must define
  quality as conformance to requirements if we
  are to manage it. Thus, those who want to talk
  about quality of life, must define that life in
  specific terms, such as desirable income, health,
  pollution control, political programs, and other
  items that can each be measured. When all
  measurement of quality of life is possible and
  practical.

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• We decided we were in the business of causing
  and measuring conformance to the requirements.
  Therefore, quality means conformance. Nonquality
  is nonconformance.

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Software quality means satisfying requirements,
both stated and implied.Greenwood, Frank,
Introduction to Computer-Integrated
Manufacturing, Harcourt Brace Jovanovich,
Publishers, Orlando, FL, 1989, page 15.Quality
means meeting the customers expectations.
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Software Quality Assurance

• Quality Attributes
• Correctness
• Fulfills Users Objective
• Meets Specifications

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Software Quality Assurance

• Quality Attributes
• Usability
• Easy to Learn How to Use it
• Easy to Run Program
• Easy to Input Data and Interpret Results

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Software Quality Assurance

• Quality Attributes
• Testability
• Easy to Devise Test to Verify Functional
  Correctness

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Software Quality Assurance

• Quality Attributes
• Repairability
• Easy to Find and Fix Errors as They Are
  Identified

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Software Quality Assurance

• Quality Attributes
• Enhanceability
• Easy to Change to Meet New Requirements

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Software Quality Terminology

• Error (mistake)
• Any unintentional or imprudent act causing a
  fault
• Fault (defect, bug)
• Any aspect of software with unanticipated
  potential to cause a failure
• Failure (crash)
• A difference between need and effect
• Incident
• Any event that needs investigation

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Software QualityMeansSatisfying
Requirements,Both Stated and Implied.

• Implied requirements increase the risk of
  customer disappointment.
• Therefore, all high priority attributes should be
  stated in the requirements specification.

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Quality Attributes Should Be Prioritized In
Requirements Specification.

• Ex. Reliability - High medium low
• Availability - High medium low

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Where is Quality?

• Requirements Specification
• Functional Specification
• Design
• Implementation
• Test Plan
• Documentation

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The most difficult problem in engineering today
is getting mistakes out of software. If you dont
share that view, you dont know how difficult the
job is.(W.W. Royce, T.R.W.)
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