1. Slides prepared by Cyndi Chie and Sarah Frye A Gift of Fire Third edition Sara Baase Chapter 8: Errors, Failures, and Risks Version modified by Cheryl Seals for Auburn University

2. What We Will Cover Can we trust computers? What can go wrong? –Failures and Errors in Computer Systems –Case Study: The Therac-25 –Increasing Reliability and Safety –Dependence, Risk, and Progress

3. Newpaper Headlines Navigation System Directs Car into River Data entry typo Mutes Millions of U.S. Pagers Flaws found in software that tracks nuclear materials Software Glitch makes wheels on scooter suddenly reverse direction IRS Computer sends bill for $68 billion in penalties Robot kills worker California Junks $100 million child support system Man arrested 5 times Due to faulty FBI Computer Data

4. Slides prepared by Cyndi Chie and Sarah Frye Q : How do we distinguish between tolerable or unavoidable errors in software versus careless software development? Version modified by Cheryl Seals for Auburn University

5. Failures and Errors in Computer Systems Most computer applications are so complex it is virtually impossible to produce programs with no errors The cause of failure is often more than one factor Computer professionals must study failures to learn how to avoid them Computer professionals must study failures to understand the impacts of poor work

6. Failures and Errors in Computer Systems (cont.) Individual Problems: Billing errors Inaccurate and misinterpreted data in databases –Large population where people may share names –Automated processing may not be able to recognize special cases –Overconfidence in the accuracy of data –Errors in data entry –Lack of accountability for errors

7. Slides prepared by Cyndi Chie and Sarah Frye Quote: It is repugnant to the principles of a free society that a person should ever be taken into police custody because of a computer error precipitated by government carelessness. As automation increasingly invades modern life, the potential for Orwellian mischief grows. --Arizona Supreme Court Version modified by Cheryl Seals for Auburn University

8. Slides prepared by Cyndi Chie and Sarah Frye Q: Describe a computer error or failure that has affected you. Version modified by Cheryl Seals for Auburn University

9. Slides prepared by Cyndi Chie and Sarah Frye Q: Who is responsible in RSI cases? What would you think about an RSI lawsuit of the maker of a tennis racket or a violin? Version modified by Cheryl Seals for Auburn University

10. Failures and Errors in Computer Systems (cont.) System Failures: AT&T, Amtrak, NASDAQ Businesses have gone bankrupt after spending huge amounts on computer systems that failed Voting system in 2000 presidential election Denver Airport Ariane 5 Rocket

11. Slides prepared by Cyndi Chie and Sarah Frye Q: Describe a recent system failure that affected many people or resulted in a great monetary loss. Version modified by Cheryl Seals for Auburn University

12. Failures and Errors in Computer Systems (cont.) Denver Airport: Baggage system failed due to real world problems, problems in other systems and software errors Main causes: –Time allowed for development was insufficient –Denver made significant changes in specifications after the project began

13. Slides prepared by Cyndi Chie and Sarah Frye Warehouse Manager software software lost $2000 on backlog orders PROBLEM Built on a system that was poorly tested and poor performance. Trying to use it on new system operating system it was not created for.Warehouse Manager software software lost $2000 on backlog orders PROBLEM Built on a system that was poorly tested and poor performance. Trying to use it on new system operating system it was not created for. Version modified by Cheryl Seals for Auburn University Failures and Errors in Computer Systems (cont.)

14. High-level Causes of Computer-System Failures: Lack of clear, well thought out goals and specifications Poor management and poor communication among customers, designers, programmers, etc. Pressures that encourage unrealistically low bids, low budget requests, and underestimates of time requirements Use of very new technology, with unknown reliability and problems Refusal to recognize or admit a project is in trouble

15. Slides prepared by Cyndi Chie and Sarah Frye Q: What activities do you participate in that are controlled by safety- critical applications? Version modified by Cheryl Seals for Auburn University

16. Failures and Errors in Computer Systems (cont.) Safety-Critical Applications: A-320: "fly-by-the-wire" airplanes (many systems are controlled by computers and not directly by the pilots) –Between 1988-1992 four planes crashed Air traffic control is extremely complex, and includes computers on the ground at airports, devices in thousands of airplanes, radar, databases, communications, and so on - all of which must work in real time, tracking airplanes that move very fast In spite of problems, computers and other technologies have made air travel safer GPWS (ground proximity warning system)-helps prevent plans from crashing into mountains

17. Case Study: The Therac-25 Therac-25 Radiation Overdoses: Massive overdoses of radiation were given; the machine said no dose had been administered at all Caused severe and painful injuries and the death of three patients Important to study to avoid repeating errors Manufacturer, computer programmer, and hospitals/clinics all have some responsibility

18. Slides prepared by Cyndi Chie and Sarah Frye Q: What determines whether the risks associated with a safety-critical application are acceptable? Version modified by Cheryl Seals for Auburn University

19. Case Study: The Therac-25 (cont.) Software and Design problems: Re-used software from older systems, unaware of bugs in previous software Weaknesses in design of operator interface Inadequate test plan Bugs in software –Allowed beam to deploy when table not in proper position –Ignored changes and corrections operators made at console

20. Slides prepared by Cyndi Chie and Sarah Frye Q: Identify the elements needed as an incentive to increase reliability and safety. Version modified by Cheryl Seals for Auburn University

21. Case Study: The Therac-25 (cont.) Why So Many Incidents? Hospitals had never seen such massive overdoses before, were unsure of the cause Manufacturer said the machine could not have caused the overdoses and no other incidents had been reported (which was untrue) The manufacturer made changes to the turntable and claimed they had improved safety after the second accident. The changes did not correct any of the causes identified later

22. Case Study: The Therac-25 (cont.) Why So Many Incidents? (cont.) Recommendations were made for further changes to enhance safety; the manufacturer did not implement them The FDA declared the machine defective after the fifth accident The sixth accident occurred while the FDA was negotiating with the manufacturer on what changes were needed

23. Case Study: The Therac-25 (cont.) Observations and Perspective: Minor design and implementation errors usually occur in complex systems; they are to be expected The problems in the Therac-25 case were not minor and suggest irresponsibility Accidents occurred on other radiation treatment equipment without computer controls when the technicians: –Left a patient after treatment started to attend a party –Did not properly measure the radioactive drugs –Confused micro-curies and milli-curies

24. If you were a judge who had to assign responsibility in this case, how much responsibility would you assign to the programmer, the manufacturer, and the hospital or clinic using the machine? Case Study: The Therac-25 Discussion Question

25. Increasing Reliability and Safety What goes Wrong? Design and development problems Management and use problems Misrepresentation, hiding problems and inadequate response to reported problems Insufficient market or legal incentives to do a better job Re-use of software without sufficiently understanding the code and testing it Failure to update or maintain a database

26. Slides prepared by Cyndi Chie and Sarah Frye Q: Identify the elements needed as an incentive to increase reliability and safety. Version modified by Cheryl Seals for Auburn University

27. Increasing Reliability and Safety (cont.) Professional techniques: Importance of good software engineering and professional responsibility User interfaces and human factors –Feedback –Should behave as an experienced user expects –Workload that is too low can lead to mistakes Redundancy and self-checking Testing –Include real world testing with real users

28. Increasing Reliability and Safety (cont.) Law, Regulation and Markets: Criminal and civil penalties –Provide incentives to produce good systems, but shouldn't inhibit innovation Warranties for consumer software –Most are sold ‘as-is’ Regulation for safety-critical applications Professional licensing –Arguments for and against Taking responsibility

29. Dependence, Risk, and Progress Are We Too Dependent on Computers? –Computers are tools –They are not the only dependence Electricity Risk and Progress –Many new technologies were not very safe when they were first developed –We develop and improve new technologies in response to accidents and disasters –We should compare the risks of using computers with the risks of other methods and the benefits to be gained

30. Do you believe we are too dependent on computers? Why or why not? Dependence, Risk, and Progress Discussion Questions

31. How do new technologies become safer? Can progress in software safety keep up with the pace of change in computer technology? Dependence, Risk & Progress Discussion Questions

32. What are acceptable rates of failure? How accurate should software be? In what ways are we safer due to new technologies? Dependence, Risk, and Progress Discussion Questions