CORNELL CS 501 - Lecture 19 Reliability 1 (35 pages)

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Lecture 19 Reliability 1



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Lecture 19 Reliability 1

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Lecture Notes


Pages:
35
School:
Cornell University
Course:
Cs 501 - Software Engineering
Software Engineering Documents

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CS 501 Software Engineering Lecture 19 Reliability 1 1 CS 501 Spring 2005 Administration 2 CS 501 Spring 2005 Lectures on Reliability and Dependability 3 Lecture 19 Reliability 1 The development process Reviews Lecture 20 Reliability 2 Different aspects of reliability Programming techniques Lecture 21 Reliability 3 Testing and bug fixing Tools CS 501 Spring 2005 Dependable and Reliable Systems The Royal Majesty From the report of the National Transportation Safety Board On June 10 1995 the Panamanian passenger ship Royal Majesty grounded on Rose and Crown Shoal about 10 miles east of Nantucket Island Massachusetts and about 17 miles from where the watch officers thought the vessel was The vessel with 1 509 persons on board was en route from St George s Bermuda to Boston Massachusetts The Raytheon GPS unit installed on the Royal Majesty had been designed as a standalone navigation device in the mid to late 1980s The Royal Majesty s GPS was configured by Majesty Cruise Line to automatically default to the Dead Reckoning mode when satellite data were not available 4 CS 501 Spring 2005 The Royal Majesty Analysis The ship was steered by an autopilot that relied on position information from the Global Positioning System GPS If the GPS could not obtain a position from satellites it provided an estimated position based on Dead Reckoning distance and direction traveled from a known point The GPS failed one hour after leaving Bermuda The crew failed to see the warning message on the display or to check the instruments 34 hours and 600 miles later the Dead Reckoning error was 17 miles 5 CS 501 Spring 2005 The Royal Majesty Software Lessons All the software worked as specified no bugs but Since the GPS software had been specified the requirements had changed stand alone system to part of integrated system The manufacturers of the autopilot and GPS adopted different design philosophies about the communication of mode changes The autopilot was not programmed to recognize valid



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