cs 4001mary jean harrold1 class 20 software safety rest of semester 11/1 (thursday) term paper...
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CS 4001Mary Jean Harrold3 Extra Credit For rest of semester, except oral presentation days (11/29, 12/4, 12/6) Bring in report for discussion Unethical or questionable behavior Preferably related to computers in society (although mine didn’t relate directly) Can use to replace one of the quick quiz grades Needs to be currentTRANSCRIPT
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Mary Jean Harrold 1 CS 4001
Class 20 Software safety Rest of semester
11/1 (Thursday) Term paper approach due 11/13 (Tuesday) Assignment 8 on software safety
(last homework assignment) 11/20 (Tuesday) Term paper due; discussion of oral
presentations 11/29, 12/6, 12/14 Oral presentations
5 minutes each; 2 minutes for questions; 9 each day Everyone prepared to present on 11/29; random ordering
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Mary Jean Harrold 2 CS 4001
Unethical or Dumb Behavior?
Fema Fakes Press Conference
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Mary Jean Harrold 3 CS 4001
Extra Credit
For rest of semester, except oral presentation days (11/29, 12/4, 12/6)
Bring in report for discussion Unethical or questionable behavior Preferably related to computers in society (although
mine didn’t relate directly) Can use to replace one of the quick quiz grades Needs to be current
![Page 4: CS 4001Mary Jean Harrold1 Class 20 Software safety Rest of semester 11/1 (Thursday) Term paper approach due 11/13 (Tuesday) Assignment 8 on software](https://reader035.vdocuments.mx/reader035/viewer/2022070605/5a4d1af57f8b9ab059980e94/html5/thumbnails/4.jpg)
Mary Jean Harrold 4 CS 4001
Can We Trust the Computer?
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Mary Jean Harrold 5 CS 4001
High Cost of Software FailureDenver Airport Baggage System (1995): $280M
Ariane 5 Explosion (1996): $7B
Mars Rover (2004): Unknown cost
Northeast Blackout (2003): $7M-$10M
Software bugs are costing the U.S. economy an estimated $59.5 billion each year. Improvements in testing, debugging, and maintenance could reduce this cost by about a third, or $22.5 billion.
(from NIST Estimated Planning Report 02-3)
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Mary Jean Harrold 6 CS 4001
What Roles Do We Play?
Computer user understand limitations of computers, need for proper training and
responsible use recognize that, as in other areas, there are good products and bad productsComputer professional studying computer failures helps us become better professionals (e.g.,
systems designer, programmers, technical support professional, etc.). even if not in these fields, will benefit from understanding sources and
consequences of failuresEducated member of society many personal decisions or social, legal, and political decisions may
depend on our understanding of risks of computer system failures could face issues of computing technology on a jury, lobbying for
legislation, or deciding whether to use an experimental medical device
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Mary Jean Harrold 7 CS 4001
What Roles Do We Play?
Computer user understand limitations of computers, need for proper training and
responsible use recognize that, as in other areas, there are good products and bad productsComputer professional studying computer failures helps us become better professionals (e.g.,
systems designer, programmers, technical support professional, etc.). even if not in these fields, will benefit from understanding sources and
consequences of failuresEducated member of society many personal decisions or social, legal, and political decisions may
depend on our understanding of risks of computer system failures could face issues of computing technology on a jury, lobbying for
legislation, or deciding whether to use an experimental medical device
![Page 8: CS 4001Mary Jean Harrold1 Class 20 Software safety Rest of semester 11/1 (Thursday) Term paper approach due 11/13 (Tuesday) Assignment 8 on software](https://reader035.vdocuments.mx/reader035/viewer/2022070605/5a4d1af57f8b9ab059980e94/html5/thumbnails/8.jpg)
Mary Jean Harrold 8 CS 4001
What Can Go Wrong?
What are risks for computer failures?
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Mary Jean Harrold 9 CS 4001
What Can Go Wrong?
What are risks for computer failures? What are reasons for computer failures? How much risk must or should we accept?
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Mary Jean Harrold 10 CS 4001
Categories of Computer Errors and Failures
Computer problems can be organized in many different ways. GF uses the following categories: Problems for individuals System failures that affect large numbers of people Problems in safety-critical applications that could
injure or kill people What are examples of each category?
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Mary Jean Harrold 11 CS 4001
Professional Responsibilities
What are they?
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Mary Jean Harrold 12 CS 4001
Professional Techniques
Software engineering has grown up around the principles of developing safe, efficient, and reliable software systems Software engineers working on safety-critical applications need
special training (Leveson—we can learn from engineers’ experience in building safe electromechanical systems)
Most software is not safe enough for safety-critical applications Accidents not prevented from technological fixes alone (no
complete automated system will work) For safety-critical systems, expert control of development and
operation is necessary
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Mary Jean Harrold 13 CS 4001
Redundancy and Self-Checking
Critical applications should be redundant e.g., Space shuttle used four identical but independent
computer systems—checked against each other most network infrastructures highly redundant.
Complex systems can collect information on their own activity for use in diagnosing and correcting errors (instrument to
monitor the application.) but sometimes the collection of systems themselves can fail
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Mary Jean Harrold 14 CS 4001
Testing
What is the purpose of testing?
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Mary Jean Harrold 15 CS 4001
Testing
Adequate and well-planned testing is essential. Test suites should be developed that exercise a
program in all likely ways it will be used (and even unusual ways) but this is impossible.
Thus, even if well tested, unforeseen set of circumstances could cause a failure.
Testing only guarantees correctness for those inputs, environments, etc. executed.
What other ways can be used to gain confidence in a system?
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Mary Jean Harrold 16 CS 4001
A Deeper Problem….
Deeper problem of “under engineered systems” Such systems are so complex, use such new
techniques, or are operating in such new ways that significant risk is inevitable—e.g., space shuttle
Systems are experimental systems. Although good management and design practices must be followed with these systems, risk cannot be eliminated.
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Mary Jean Harrold 17 CS 4001
Law and Regulation
Criminal and civil penalties are always available for computing systems that fail and cause harm. But this is after the fact.
Retail sellers of computing hardware usually provide warranties. However, software is usually sold “as-is.” What should the law be? Should companies be required by law to pay for bugs (and in what way?) or should they be protected?
Safety-critical applications are a special case. Perhaps they need FDA-like regulation?
Do any of them have FDA-like regulation?
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Mary Jean Harrold 18 CS 4001
Professional Licensing
Software development professionals could be licensed (like engineers or architects).
Licensing typically involves specific training, passing of competency exams, ethical requirements, and continuing education.
But sometimes licensing is used to protect the status-quo rather than to provide better and more ethical service. Economic analysis shows that one effect of licensing is to reduce the number of practitioners in a field and keep prices and income higher than they would otherwise be.
What is the current status of software-engineering licensing?
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Mary Jean Harrold 19 CS 4001
Discussion
Are we too dependent on computers? How does modeling help improve reliability?
What are the problems and risks in modeling? Who are the “good guys”—those people or
organizations that make systems safer or reduce negative consequences of errors?
When testing usually produces no failures, managers want to reduce the testing performed. Do you agree or disagree with this approach?
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Mary Jean Harrold 20 CS 4001
Discussion
How many of you would ride on a computer controlled train that had no human driver?
How many of you would ride on a computer controlled train that had no human, on-board pilot?
How many of you would be among the first to get a computer chip implanted in your brain to aid in memory or computation?
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Mary Jean Harrold 21 CS 4001
Discussion
Which models do you think would produce accurate results? Less reliable? Why? Models that predict the position of the moon in
relation to the earth 30 years from now Models that predict the speed of a new racing boat
hull design under specified wind conditions. Models that predict the effect of an income tax
change on government revenue.