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Was modified by hospital technicians to compute

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was modified by hospital technicians to compute modified doses of radiation for each patient. Think of other factors (Security for example) CS352 Software Engineering II
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Achieving S/W Quality Critical success factors: Software Engineering Methods Project Management Techniques Quality Control Dr. Omar Hamdy Spring 2011 19 Quality Assurance CS352 Software Engineering II
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S/W Reliability Reliability: Probability of a failure occurring in operational use A personal computer that crashes frequently vs. a machine that is out of service for two days A database system that crashes frequently but Dr. Omar Hamdy Spring 2011 20 comes back quickly with no loss of data v. a system that fails once in three years but data has to be restored from backup. A system that does not fail but has unpredictable periods when it runs very slowly. CS352 Software Engineering II
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Reliability Metrics Traditional Measures Mean time between failures Availability (up time) Mean time to repair Market Measures Dr. Omar Hamdy Spring 2011 21 – Complaints Customer retention User Perception is Influenced by Distribution of failures Example (hypothetical): Cars are less safe than trains in accidents per hour, but safer in accidents per mile CS352 Software Engineering II
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Requirements Specification of System Reliability Example: ATM card reader Failure class Example Metric Permanent System fails to operate 1 per 1,000 days non-corrupting with any card -- reboot Dr. Omar Hamdy Spring 2011 22 CS352 Software Engineering II Transient System can not read 1 in 1,000 transactions non-corrupting an undamaged card Corrupting A pattern of Never transactions corrupts database
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Cost of Reliability Improvement $ Dr. Omar Hamdy Spring 2011 23 CS352 Software Engineering II Up time 99% 100%
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