Ian sommerville 2004 slide 26 software engineering

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Unformatted text preview: l systems unless it is actually needed. As well as testing for what the system should do, you may also have to test for what the system should not do. Do not have a default exception handling response which is system shut-down in systems that have no fail-safe state. Ian Sommerville 2004 Slide 27 Software Engineering Case Studies Lessons learned In critical computations, always return best effort values even if the absolutely correct values cannot be computed. Wherever possible, use real equipment and not simulations. Improve the review process to include external participants and review all assumptions made in the code. Ian Sommerville 2004 Slide 28 Software Engineering Case Studies Avoidable failure The designer's of Ariane 5 made a critical and elementary error. They designed a system where a single component failure could cause the entire system to fail. As a general rule, critical systems should always be designed to avoid a single point of failure. Ian Sommerville 2004 Slide 29 Software Engineering Case Studies EMP 5117 Foundations of software engineering Examples of software engineering failures or shortcomings and the outsourcing phenomenon. by Daniel Gauthier Stella Kemdirim Xingmin Cao University of Ottawa 19th of January 2005 Therac-25, Medical Linear Accelerator The Therac-25 is a medical linear accelerator. It accelerates electrons to create high-energy beams that can destroy tumours with minimal impact on the surrounding healthy tissue. Therac-25, The First Accident Kennestone Regional Oncology Center, Marietta, Georgia June1985 After undergoing a lumpectomy to remove a malignant breast tumor, a 61-year-old woman was receiving follow-up radiation treatment: When the machine turned on, she felt a "tremendous force of heat . . . this red-hot sensation." When the technician came in, she said, "You burned me!!" The technician replied that that was not possible. Later, the patient had a burn going through her body, the swollen area had begun to slough off layers o...
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