Chapter 7 Software Development A Textbook aimed at protecting consumers Software Quality Links Ian Foster and Grid Computing The Risks Digest

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Chapter 7Software Development A Textbook
aimed at protecting consumersSoftware Quality
LinksIan Foster and Grid ComputingThe Risks
Digest
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Chapter 7 - Objectives

1. Discuss the need for quality software in business
   systems, industrial process control systems, and
   consumer products.
2. Discuss the ethical issues in software
   manufacturing.
3. Identify the four most common types of software
   product liability claims.
4. Identify the essential components of a software
   development methodology.
5. Discuss the use of the Capability Maturity Model.
6. Define what a safety-critical system is.

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Strategies to Engineer Quality Systems

• A software defect is any error that, if not
  removed, would cause a system to fail to meet the
  needs of its users.
• Software quality is the degree to which the
  attributes of a software product enable it to
  meet the needs of its users.

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Strategies to Engineer Quality Systems

• Quality management address how to define,
  measure, and refine the quality of the
  information systems development process and
  product.
• Deliverables are the items developed during the
  development process (flowcharts, documentation,
  software, etc.)

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Software Quality

• Software is used to control many business and
  industrial processes.
• The impact of a software defect can be
  devastating and result in upset customers and the
  eventual loss or reduction in revenue.

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Legal Overview

• Product liability is the liability of
  manufacturers, sellers, leasers, and others for
  the injuries caused by defective products.
• Strict liability means that the defendant is
  responsible for injuring another person
  regardless of negligence or intent.

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Legal Overview

• Under negligence, a software supplier cannot be
  held responsible for every product defect that
  causes customer or third party loss.
• Responsibility is limited to harmful defects that
  could have been detected and corrected through
  reasonable software development practices.
• Legal Fix for Software Flaws?

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Legal Overview

• Warranty assures the buyer that a product meets
  certain standards of quality.
• If a product fails to meets its warranty, the
  customer can sue the seller for breach of
  warranty.
• Intentional misrepresentation occurs when a
  seller misrepresents the quality of a product.
• Open Sourcewhos responsible? An interesting
  article

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From Osler

• In assessing whether a design defect is present,
  the factors that the court will consider,
  frequently with the assistance of expert
  evidence, will include
• The utility of the product and the likelihood of
  injury resulting from its use
• Whether the design was influenced by a desire to
  prevent more likely types of injuries
• The extent of the testing done during the design
  process
• Whether there were internally or externally
  established standards which were breached
• The availability of alternative designs that
  could have reduced or eliminated the risks at a
  reasonable cost and with limited impact on
  functionality
• The reasonable expectations of safety and utility
  of consumers or users of the product.

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Software Development Process

• Developing information system software is a
  complex activity.
• A system development methodology enables systems
  analysts, programmers, project managers, and
  others to make controlled and orderly progress in
  developing high-quality software.

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System Development Process

• Software quality assurance refers to those
  methods within the software development
  methodology that are used to guarantee that
  software being developed will operate reliably.

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System Testing

• Dynamic testing is testing code by entering test
  data and comparing actual results to expected
  results.
• Black-box testing involves viewing the software
  unit as a device that has expected input and
  output behaviors but whose internal workings are
  unknown.
• White-box testing involves viewing the software
  unit as a device that has expected input and
  output behaviors but whose internal workings are
  known.

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System Testing

• Static testing is running an analyzer software
  that looks for suspicious patterns in programs
  that might indicate a software defect.
• Integration testing ensures that all linkages
  among various subsystems work successfully.

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System Testing

• System testing is conducted to test the entire
  system as a complete entity.
• User acceptance testing is an independent test
  performed by trained end users to ensure that the
  system operates as expected from their
  viewpoints.

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Capability Maturity Model

• Carnegie Mellon Institute developed the
  Capability Maturity Model for Software.
• It defines five levels of software development
  process maturity and identifies the issues most
  critical to software quality and process
  improvement.

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Capability Maturity Model
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Development of Safety-Critical Systems

• A safety-critical system is one whose failure may
  cause injury or death to human beings.
• Risk is the product of probability of an
  undesirable event occurring times the magnitude
  of the consequence of the event happening.
• Therac-25 example

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Development of Safety Critical Systems

• Redundancy is the provision of multiple
  interchangeable components to perform a single
  function in order to cope with failures and
  errors.
• Reliability is the probability of a component or
  system performing its mission over a certain
  length of time.

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Development of Safety-Critical Systems

• One of the most important and difficult areas of
  safety-critical systems design is the
  human-system interface.
• Poor human-system interfaces can greatly increase
  risk, sometimes with tragic consequences. (Risks
  Digest)

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Quality Management Standards

• The International Organization for
  Standardization issued the ISO series of business
  management standards in 1988.
• ISO 9000 is a series of formal standards to
  follow when developing quality information
  systems.

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ISO 9000

• To be ISO 9000 certified, a company must do three
  things
• Have written procedures for everything they do.
• Follow those procedures.
• Prove to an auditor that they have written
  procedures and that they follow them.

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ISO 9000

• ISO 9001 Design, development, production,
  installation, service
• ISO 9002 Production, installation, service
• ISO 9003 Final inspection and test
• ISO 9004 Quality management and quality systems
  elements

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Failure Mode and Effects Analysis

• FMEA is an important technique used to develop
  any ISO 9000 compliant systems.
• FMEA is used as a reliability evaluation
  technique to determine the effect of system and
  equipment failure.
• Failures are classified on their impact on
  mission success, personnel safety, equipment
  safety, customer satisfaction, and customer
  safety.

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Summary

• High-quality software systems are needed because
  they are easy to learn and easy to use, perform
  the functions that meet users needs, and have a
  high degree of availability.
• There are many ethical issues facing software
  developers. The impact of software defects can
  have devastating effects.
• Software product liability claims are frequently
  based on strict liability, negligence, breach of
  warranty, or misrepresentation.

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Summary

• A software development methodology defines the
  activities in the system development process.
• An effective system development methodology
  protects software manufacturers from legal
  liability for defective software.
• The Capability Maturity Model defines five levels
  of software development process.

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Case 1 - Airbags

• Airbags deploy at 140 mph unleashing too much
  energy for smaller people and children. Auto
  makers are working to make airbags more safe.
  Some argue that airbag technology is too
  complicated. They say educating the public would
  be better.

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Case 2 - Patriot Missile

• On February 25, 1991, a Patriot missile defense
  system in Saudi Arabia failed to track and
  intercept an incoming scud missile because of a
  software problem. The incoming missile hit an
  Army barracks and killed twenty-eight Americans.