Download Dependable Computing - Final Exam 2003 | CS 686 and more Exams Computer Science in PDF only on Docsity!
. This is a closed book, closed notes examination. . Write your answers on the examination paper in ink or legible pencil. . If your answer cannot be read or understood , or if your answer is vague or confused, it will be marked wrong. . In any question, make any assumptions that you need to but document your assumptions. . The number in parentheses after each question is the number of points allocated to that ques- tion.
NAME ( Print Legibly. All Capitals ):
PLEDGE ( Write Out In Full And Sign ):
Graduate Students (CS651) Sections A and B
Undergraduate Students (CS551) Section A
CS 551/CS
DEPENDABLE C OMPUTING
FINAL EXAMINATION
FALL 2003
Final Examination - Three Hours
SECTION A
- Dependable computing is important for applications that have serious consequences of failure. List the major categories of loss that might be incurred when a computing system fails. (5)
- What are the four different approaches to dealing with faults and in what order should they be applied. (5)
- Give the definition of erroneous state. (5)
- Give the definition of reliability. (5)
- The manufacturer of the computerized dispatching system (the 911 system) being considered for Gotham City’s ambulance service claimed that the system availability is 0.99999. The mayor decided that this level of availability was excellent and had the system installed. Lengthy outages have occurred since installation leading to ambulances not being dispatched when needed. The manufacturer claims that the system is meeting its dependability require- ment and has been absolved of blame. How can this be the case? (10)
Page score
- Briefly but carefully explain what is meant by statistical (or life) testing as applied to elements of a computer system. (10)
- Briefly but carefully explain the appropriate role of statistical testing in safety-critical soft- ware development. (10)
- Consider the following fragment of source code in a hypothetical programming language:
PressureAlarm := (Pressure < PLimit); if (Temp > TLimit) and PressureAlarm then if CoolingPumpState = On then EmergencyIndicator := On; else ReactantPump := On; endif; endif;
(a) What are the decisions in this code in the sense of MC/DC test coverage? (5)
(b) What are the conditions in this code in the sense of MC/DC test coverage? (5)
Page score
- Using a mathematical notation, define the set that consists of the integers that are not divisible by five or eight (use “mod” as a remainder operator). (5)
- Assuming the given set [UVAStudents] is the set of all students enrolled at the university of Virginia, defining any other items that you need, and using a mathematical notation:
(a) Define the set consisting of all the graduate students in CS651. (5)
(b) Define a predicate that is true if and only if there are more graduate students in the class than undergraduates. (5)
- An ICU hospital patient is monitored by a set of body temperature sensors and a set of body electrical sensors. The hospital procedures require that the staff be informed if any two tem- perature sensors detect values above MaxTemp, if any two electrical sensors detect values below MinVoltage, or if one temperature sensor detects a value below MinTemp and an elec- trical sensor reads a value of Zero. Carefully formalize this statement in a mathematical nota- tion. Assume temperature_sensor and a electrical_sensor types. (10)
Page score
S ECTION B
- Carefully and concisely explain the statement “Formal languages are closed.” (15)
- Using a piece of program in any language (syntax doesn’t matter) as an example, explain what the Consistent Comparison Problem is and show how it arises. (15)
Page score
- The thermostat for the heating system described in question 17 uses a microprocessor with three inputs: (1) an integer representing the current temp; (2) an integer representing the desired temp; and (3) a binary indicating system ON/OFF. It has a single binary output that turns the furnace on and off. An internal clock is available in the form of an integer that counts seconds since the system was installed. For maintenance purposes, the microprocessor has to keep track of the total operating time of the furnace. Outline a Z specification for the operation of the thermostat (syntactic detail does not matter, the principles do). (30)
