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Chapter 8
Multiple-choice Questions (with answers and references to the text)
1. Most of the delay in the opening of the Denver International Airport was because of
problems with
(a) the air traffic control system
(b) the environmental monitoring systems
(c) the baggage handling system
(d) the telephone and communications systems
2. One of the sources of failure common to BOTH the Therac-25 and the Ariane 5 rocket
was
(a) confusing and poorly-documented error messages
(b) poor human-computer interface design
(c) operator error
(d) reuse of software from previous versions of the systems
3. Which of the following occupations can sometimes cause Repetitive Strain Injuries
(RSI)?
(a) Sign-language interpreter for the deaf
(b) Musician
(c) Computer programmer
(d) All of the above
True/False
______ Some computer errors are actually system failures, in that it was the human/computer
interface which caused the resulting problem.
______ The cause of failure in a computer program is often due to more than one factor.
______ Legacy systems are typically reliable, but inflexible.
______ U.S. and European pilots are now trained to follow Traffic Collision Avoidance System
(TCAS) instructions even if they conflict with instructions from an air traffic controller.
______ Redundancy and self-checking are often present in safety-critical systems.
______ A feature of high reliability organizations is loose structure.
Short-answer Questions
1. List two principles for producing software that might have prevented the crash
of American Airlines Flight 965 near Cali, Columbia in 1995. Briefly describe
what each one is and how it might have made a difference.
2. Briefly explain the Therac-25 case. What happened? What are some reasons the
machine failed? Why were there so many incidents?
Matching Questions
Essay Questions
1. Some people have proposed establishing legal standards and regulations to
govern safety-critical computer-based systems.
a. Give and explain a few of the best arguments for and against such a proposal
(at least two on each side). Give counter-arguments against the arguments
for each side.
Note: the "counter-arguments" you are asked to give should oppose or
answer the arguments on the other side as directly and convincingly as
possible. They should not be simply unrelated arguments on the opposite
side of the issue.
b. Describe two provisions that may be included in such regulations. How
effective do you feel each provision would be?
2. a. Describe the role the manufacturer, the hospitals/clinics, and the programmer
each played in the Therac-25 radiation overdose incidents.
b. Briefly describe how professional techniques for increasing reliability and
safety could have prevented the problems.
3. a. Briefly describe the major factors that contributed to the failure of each of the
following: the Denver Airport baggage system failure, the Ariane 5 rocket
malfunction, and an A320 Airbus crash.
b. Briefly describe how professional techniques for increasing reliability and
safety could have prevented these failures.
