Intro - 272: Software Engineering Fall 2008 Instructor:...

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272: Software Engineering Fall 2008 Instructor: Tevfik Bultan Lecture 0: Introduction
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Software Engineering In 1968 a seminal NATO Conference was held in Germany. Purpose: to look for a solution to software crisis 50 top computer scientists, programmers and industry leaders got together to look for a solution to the difficulties in building large software systems (i.e., software crisis) The term “ software engineering ” was first used in that conference to indicate a systematic, disciplined, quantifiable approach to the production and maintenance of software Three-decades later (1994) an article in Scientific American (Sept. 94, pp. 85-96) by W. Wayt Gibbs was titled: “Software’s Chronic Crisis’’
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Software’s Chronic Crisis Large software systems often: Do not provide the desired functionality Take too long to build Cost too much to build Require too much resources (time, space) to run Cannot evolve to meet changing needs For every 6 large software projects that become operational, 2 of them are canceled On the average software development projects overshoot their schedule by half 3 quarters of the large systems do not provide required functionality
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Software Failures There is a long list of failed software projects and software failures You can find a list of famous software bugs at: http://www5.in.tum.de/~huckle/bugse.html I will talk about two famous and interesting software bugs
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Ariane 5 Failure A software bug caused European Space Agency’s Ariane 5 rocket to crash 40 seconds into its first flight in 1996 ( cost: half billion dollars ) The bug was caused because of a software component that was being reused from Ariane 4 A software exception occurred during execution of a data conversion from 64-bit floating point to 16-bit signed integer value The value was larger than 32,767, the largest integer storable in a 16 bit signed integer, and thus the conversion failed and an exception was raised by the program When the primary computer system failed due to this problem, the secondary system started running. The secondary system was running the same software, so it failed too!
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The programmers for Ariane 4 had decided that this particular velocity figure would never be large enough to raise this exception. Ariane 5 was a faster rocket than Ariane 4! The calculation containing the bug actually served no purpose once the rocket was in the air. Engineers chose long ago, in an earlier version of the Ariane rocket, to leave this function running for the first 40 seconds of flight to make it easy to restart the system in the event of a brief hold in the countdown. You can read the report of Ariane 5 failure at:
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Intro - 272: Software Engineering Fall 2008 Instructor:...

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