Software development
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This document discusses strategies for engineering high-quality software, including defining a rigorous development methodology, learning from past mistakes, and designing systems to be robust against human error. It also covers legal issues around software product liability, common types of claims, and defenses. The document outlines the components of an effective software development process, including roles, testing approaches, and maturity models to assess and improve processes. Special precautions for safety-critical systems are also discussed.
Software development
- 1. Ethics in Information Technology Chapter 7 Software Development
- 2. Objectives • Why do companies require high-quality software in business systems, industrial process control systems, and consumer products? • What ethical issues do software manufacturers face in making tradeoffs between project schedules, project costs, and software quality?
- 3. Objectives (continued) • What are the four most common types of software product liability claims, and what actions must plaintiffs and defendants take to be successful? • What are the essential components of a software development methodology, and what are its benefits?
- 4. Objectives (continued) • How can Capability Maturity Model Integration improve an organization’s software development process? • What is a safety-critical system, and what actions are required during its development?
- 5. Strategies to Engineer Quality Software • High-quality software systems – Operate safely and dependably – Have a high degree of availability – Required to support the fields of • Air traffic control • Nuclear power • Automobile safety • Health care • Military and defense • Space exploration
- 6. Strategies to Engineer Quality Software (continued) • More and more users are demanding high quality software • Software defect – Could cause a system to fail to meet users’ needs – Impact may be trivial or very serious – Patches may contain defects • Software quality – Degree to which software meets the needs of users
- 7. Strategies to Engineer Quality Software (continued) • Quality management – How to define, measure, and refine the quality of the development process and products – Objective • Help developers deliver high-quality systems that meet the needs of users • Deliverables – Products such as: • Statements of requirements • Flowcharts • User documentation
- 8. Strategies to Engineer Quality Software (continued) • Primary cause for poor software quality – Developers do not know how to design quality into software – Or do not take the time to do so • Developers must – Define and follow a set of rigorous engineering principles – Learn from past mistakes – Understand the environment in which systems operate – Design systems relatively immune to human error
- 9. Strategies to Engineer Quality Software (continued) • Programmers make mistakes in turning design specifications into code – About one defect for every 10 lines of code • Pressure to reduce time-to-market • First release – Organizations avoid buying the first release – Or prohibit its use in critical systems – Usually has many defects
- 10. The Importance of Software Quality • Business information systems are a set of interrelated components – Including • Hardware • Software • Databases • Networks • People • Procedures
- 11. The Importance of Software Quality (continued) • Business information system examples – Order-processing system – Electronic-funds transfer system – Airline’s online ticket reservation system • Decision support system (DSS) – Used to improve decision making • Software for industrial use • Software controls the operation of many industrial and consumer products
- 12. The Importance of Software Quality (continued) • Mismanaged software can be fatal to a business • Ethical questions – How much effort and money to invest to ensure high-quality software – Whether products could cause damage • Legal exposure if they did
- 13. Legal Overview: Software Product Liability • Product liability – Liability of manufacturers, sellers, lessors, and others for injuries caused by defective products – There is no federal product liability law • Mainly state law • Article 2 of the Uniform Commercial Code • Strict liability – Defendant held responsible for the injury – Regardless of negligence or intent
- 14. Legal Overview: Software Product Liability (continued) • Strict liability – Plaintiff must prove only that the software product is defective or unreasonably dangerous and that the defect caused the injury – No requirement to prove that the manufacturer was careless or negligent • Or to prove who caused the defect – All parties in the chain of distribution are liable
- 15. Legal Overview: Software Product Liability (continued) • Legal defenses used against strict liability – Doctrine of supervening event – Government contractor defense – Expired statute of limitations • Negligence – A supplier is not held responsible for every product defect that causes a customer or third- party loss – Responsibility is limited to defects that could have been detected and corrected through “reasonable” software development practices
- 16. Legal Overview: Software Product Liability (continued) • Negligence – Area of great risk for software manufacturers – Defense of negligence may include • Legal justification for the alleged misconduct • Demonstrate that the plaintiffs’ own actions contributed to injuries
- 17. Legal Overview: Software Product Liability (continued) • Warranty – Assures buyers or lessees that a product meets certain standards of quality – Expressly stated – Implied by law • Breach of warranty claim – Plaintiff must have a valid contract that the supplier did not fulfill – Can be extremely difficult to prove • Because the software supplier writes the warranty
- 18. Legal Overview: Software Product Liability (continued) • Intentional misrepresentation – Seller or lessor either misrepresents the quality of a product – Or conceals a defect in it – Forms of representation • Advertising • Salespersons’ comments • Invoices • Shipping labels
- 19. Software Development Process • Large software project roles – System analysts – Programmers – Architects – Database specialists – Project managers – Documentation specialists – Trainers – Testers
- 20. Software Development Process (continued) • Software development methodology – Work process – Controlled and orderly progress – Defines activities and individual and group responsibilities – Recommends specific techniques for accomplishing various activities – Offers guidelines for managing the quality of software during various stages of development
- 21. Software Development Process (continued) • Safer and cheaper to avoid software problems at the beginning than to attempt to fix damages after the fact – Identify and remove errors early in the development process • Cost-saving measure • Most efficient way to improve software quality
- 22. Software Development Process (continued) • Effective methodology – Reduces the number of software errors that might occur – If an organization follows widely accepted development methods, negligence on its part is harder to prove • Software quality assurance (QA) refers to methods within the development cycle – Guarantee reliable operation of product – Ideally applied at each stage throughout the development cycle
- 23. Software Development Process (continued) • Dynamic testing – Black-box testing • Tester has no knowledge of code – White-box testing • Testing all possible logic paths through the software unit • With thorough knowledge of the logic • Make each program statement execute at least once
- 24. Software Development Process (continued) • Static testing – Static analyzers are run against the new code – Looks for suspicious patterns in programs that might indicate a defect • Integration testing – After successful unit testing – Software units are combined into an integrated subsystem – Ensures that all linkages among various subsystems work successfully
- 25. Software Development Process (continued) • System testing – After successful integration testing – Various subsystems are combined – Tests the entire system as a complete entity • User acceptance testing – Independent testing – Performed by trained end users – Ensures that the system operates as they expect
- 26. Capability Maturity Model Integration for Software • Process improvement approach • Defined by the Software Engineering Institute – At Carnegie Mellon University in Pittsburgh • Defines essential elements of effective processes • General enough to evaluate and improve almost any process • Frequently used to assess software development practices
- 27. Capability Maturity Model Integration for Software (continued) • Defines five levels of software development maturity • Identifies issues most critical to software quality and process improvement • Organization conducts an assessment of its software development practices – Determines where they fit in the capability model – Identifies areas for improvement • Action plans are needed to upgrade the development process
- 28. Capability Maturity Model Integration for Software (continued) • Maturity level increases – Organization improves its ability to deliver good software on time and on budget
- 30. Key Issues in Software Development • Consequences of software defects in certain systems can be deadly – Companies must take special precautions
- 31. Development of Safety-Critical Systems • Safety-critical system – Failure may cause injury or death – Examples • Automobile’s antilock brakes • Nuclear power plant reactors • Airplane navigation • Roller coasters • Elevators • Medical devices
- 32. Development of Safety-Critical Systems (continued) • Key assumption – Safety will not automatically result from following the organization’s standard development methodology • Must go through a more rigorous and time- consuming development process than other kinds of software • All tasks require – Additional steps – More thorough documentation – More checking and rechecking
- 33. Development of Safety-Critical Systems (continued) • Project safety engineer – Explicit responsibility for the system’s safety – Uses a logging and monitoring system • To track hazards from the project’s start to finish • Hazard log – Used at each stage of the software development process – Assesses how it has accounted for detected hazards
- 34. Development of Safety-Critical Systems (continued) • Safety reviews – Held throughout the development process • Robust configuration management system – Tracks all safety-related documentation • Formal documentation required – Including verification reviews and signatures • Key issue – Deciding when QA staff has performed enough testing
- 35. Development of Safety-Critical Systems (continued) • Risk – Probability of an undesirable event occurring times the magnitude of the event’s consequences if it does happen – Consequences include • Damage to property • Loss of money • Injury to people • Death
- 36. Development of Safety-Critical Systems (continued) • Redundancy – Provision of multiple interchangeable components to perform a single function – In order to cope with failures and errors • N-version programming – Form of redundancy – Involves the execution of a series of program instructions simultaneously by two different systems – Uses different algorithms to execute instructions that accomplish the same result
- 37. Development of Safety-Critical Systems (continued) • N-version programming – Results from the two systems are compared – If a difference is found, another algorithm is executed to determine which system yielded the correct result – Instructions for the two systems are: • Written by programmers from two different companies • Run on different hardware devices – Both systems are highly unlikely to fail at the same time under the same conditions
- 38. Development of Safety-Critical Systems (continued) • Decide what level of risk is acceptable – Controversial – If the level of risk in a design is judged to be too great, make system modifications • Mitigate the consequences of failure – By devising emergency procedures and evacuation plans • Recall product – When data indicates a problem
- 39. Development of Safety-Critical Systems (continued) • Reliability – Probability of a component or system performing without failure over its product life • Human interface – Important and difficult area of safety-critical system design – Leave the operator little room for erroneous judgment
- 40. Quality Management Standards • ISO 9000 standard – Guide to quality products, services, and management – Organization must submit to an examination by an external assessor – Requirements: • Written procedures for everything it does • Follow those procedures • Prove to the auditor the organization fulfilled the first two requirements
- 41. Quality Management Standards (continued) • Failure mode and effects analysis (FMEA) – Used to evaluate reliability – Determine the effect of system and equipment failures – Goal: • Identify potential design and process failures early in a project
- 42. Quality Management Standards (continued) • Failure mode and effects analysis (FMEA) – Failure mode • Describes how a product or process could fail – Effect • Adverse consequence that a customer might experience – Seldom is a one-to-one relationship between cause and effect
- 43. Quality Management Standards • DO-178B/EUROCCAE ED-128 – Evaluation standard for the international aviation community – Developed by Radio Technical Commission for Aeronautics (RTCA)
- 44. Manager’s Checklist for Improving Software Quality
- 45. Summary • More and more users are demanding high quality software • Software product liability claims are frequently based on – Strict liability – Negligence – Breach of warranty – Misrepresentation
- 46. Summary (continued) • Software development methodology – Defines activities in the software development process – Defines individual and group responsibilities – Recommends specific techniques – Offers guidelines for managing the quality of products • CMMI – Defines five levels of software development maturity • Safety-critical system – Failure may cause injury or death